Term Test 3 Flashcards

Question

Oxygen, ATP and NADPH in light dependent reactions

Answer 1

-light dependant reactions use energized electrons from PSII to produce ATP, generate oxygen via photolysis and use re-energized electrons from PSI to produce NADPH -in photosynthesis, the efficiency of conversion of light energy into chemical energy is about 27% -solar panels convert light energy into electricity at a photosynthetic efficiency of 10-20%

Answer 2

-primitive photosystems -PSI can work independently of PSII -energized electrons from P700 are recycled back via ferredoxin to plastoquinone instead of being passed on to NADP+ reductase -electrons pass back down to PSI driving H+ transport across the thylakoid membrane, making more ATP -no water molecules are split, so no oxygen or NADPH produced

Answer 3

-light independent reaction uses light energy and H2O to yield chemical energy in the form of ATP and NADPH -light independent reaction or calvin cycle takes place in the chloroplast stroma, uses chemical energy produced in light-dependent reactions to make simple sugar phosphates, often called dark reactions -cellular stockpiles of ATP and NADPH only last a few seconds or minutes and must be replenished again

Answer 4

-first product of the calvin cycle is a 3- carbon sugar compound -also known as the C3 pathway

Answer 5

1. one ATP powers the addition of a phosphate to a 5-carbon sugar phosphate 2. CO2 is added to the 5-carbon sugar phosphate (catalyzed by Ribulose 1,5 biphosphate carboxylase/oxygenase RUBISCO enzyme). the resulting 6-carbon molecule is unstable and short lived. it breaks down into two 3-carbon molecules (3-phosphoglycerate, PGA) 3. two molecules of ATP add phosphates to PGA. two PGA molecules are converted into two 1,3-bisphosphoglycerate (BPG) 4. BPG is reduced by NADPH into glyceraldehyde-3-phosphate (G3P) 5. one G3P per three turns of the cycle contributes to sugars. majority of G3P continues through the rest of the cycle to replenish RuBP 6. ATP from light dependent reaction is used to phosphorylate Ru5p to regenerate RuBP

Answer 6

-three turns to generate one G3P molecule thus 6 turns to make on 6-carbon sugar After 6 turns: -18 ATP -12 NADPH

Answer 7

-18 ATP and 12 NADPH (3:2) -equal ratio of molecules is created by the light dependant reaction -extra ATP comes from the cyclic electron flow that takes place in PSI

Answer 8

-once 6-carbon sugar is produced it can remain in chloroplast and be made into starch, or be transported to other areas of cell (mitochondria) or plant roots as sucrose

Answer 9

-about 95% of plant biomass use C3 fixation -all woody trees and temperate crop species, including rice, wheat, soybeans, and barley are C3 plants -3 PGA first product of fixation by RubisCO

Answer 10

-light dependant and light independent reactions both occur in mesophyll cells -no chloroplasts in bundle sheath cells, parenchyma used for conduction

Answer 11

-the movement of sugar and other organic molecules can be either symplastic (and transmembrane) or apoplastic -sieve tube members stack on top of one another -porous sieve plates between tubes allow continuous cytosolic flow (no need to cross cell wall or membrane) -sieve tubes lack nuclei, rely on companion cells fro protein synthesis, still alive at maturity (symplast. present)

Answer 12

-energy is required to move sucrose molecules from the apoplasm to the symplasm of sieve and companion cells -a H+ gradient, initially generated by a proton pump, is used to co-transport one sucrose molecule with every H+ ion

Answer 13

-sugar source is the part fo the plant that produces sugars (leaves, green stem) -sugar sink is a part of the plant that mainly consumes or stores sugar (roots, stem, and fruits) -sink in summer can become source in winter -sugar is not always transported by phloem, remember shoots are sink in the spring (maple syrup) -sugar transport is driven by water uptake through osmosis

Answer 14

-sugar produced in leaves, is transported through phloem to roots (shoot to roots) -sugar enters sieve tube member and drives water uptake due to the osmotic potential that it generates -the turgor pressure generated moves water and sugar down the phloem until sugar is unloaded into sink tissues such as roots

Answer 15

1. at the source, sugar enters by active transport into sieve tubes. water potential of sieve tube decreases and water enters by osmosis 2. the turgor pressure generated moves water and sugar down the sieve tubes towards sinks. mass flow from high to low pressure 3. sugar is actively unloaded at sink and water exits sieve tubes, lowering water pressure in sieve tubes 4. water diffuses back into xylem -active transport (symplastic) is required, hence sieve tubes and companion cells are "alive"

Answer 16

-in photosynthesis the estimated efficiency of converting light energy into chemical energy is 27% -the overall energy conversion into biomass is about 4-6% -low because of Ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO)

Answer 17

-key enzyme that fixes carbon in the calvin cycle -most abundant protein on earth -both carboxylase and oxygenase -has existed for a long time since the atmosphere had little to no free oxygen

Answer 18

Photosynthesis: RubisCO functions as a carboxylase, adds a carbon from CO2 Photorespiration: RubisCO functions as a oxygenase, adds oxygen from O2 - 2-PG produced by photorespiration can eventually be broken down by mitochondria to release CO2. no Atp is produced -RubisCO's affinity for CO2 is not strong, O2 produced during photosynthesis can block carbon fixation

Answer 19

-as temperature increases, so does evaporation/water loss through leaves -stomata close in response to excess water loss -closing stomata conserves water but CO2 is locked out and O2 is trapped in the leaf; photorespiration rates increase

Answer 20

-high light -high temperature -low water -low CO2 -high O2

Answer 21

-moderate light -moderate temperature -sufficient water -high CO2 -low O2

Answer 22

-to reduce photorespiration, some plant species have developed pathways that minimize oxygen exposure to RubisCO -C4 fixation occurs in warm and arid regions; mostly grasses (corn, sorghum, sugar cane) with some cold-tolerant shrubs and tropical angiosperms - about 3% of flowering plants

Answer 23

-most C4 plants have a distinctive leaf anatomy called Kranz anatomy -spacial separation of C4 pathways (mesophyll) and Calvin cycle (bundle sheath)

Answer 24

-in C4 plants the first detectable product of CO2 fixation is a 4 carbon molecule, oxaloacetate (OAA) 1. OAAis formed when CO2 is fixed to phosphoenolpyruvate ) PEP by PEP carboxylase (PEPC) in the chloroplast stroma of mesophyll cells 2. OAA is converted to malate (or aspartate) and moved into the bundle sheath cells through the symplast (plasmodesmata) 3. once inside the bundle sheath cells, the malate is decarboxylated to yield CO2 and pyruvate in the chloroplast stroma 4. the released CO2 then enters the Calvin cycle (C3 fixation) 5. the pyruvate recycles back to the mesophyll cell chloroplasts where it is phosphorylated to regenerate PEP

Answer 25

-the C4 pathway allows bundle sheath cells to maintain a high concentration fo CO2 thereby favouring binding of RubisCO to CO2 rather than O2 -PEP carboxylase has a high affinity for the hydrated form of CO2 (HCO3-, bicarbonate ion) and is not affected by the presence or concentration of O2 -CO2 released by photorespiration can also be re-fixed by the C4 pathway

Answer 26

1. optimal temperature range for C4 photosynthesis is much higher 2. C4 plants can attain the same photosynthetic rate as C3 plants but with smaller stomatal openings and hence with less water loss 3. C4 plants have 3-6 times less RubisCO than C3 plants 4. overall, C4 plants are able to use nitrogen and water more efficiently than C3 plants

Answer 27

-Kranz anatomy is not required for C4 fixation to occur, several known Chenopodiaceae plant species achieve spatial separation in a single cell type -peripheral chloroplast compartments (PCC, C4 fixation) and central chloroplast compartments (CCC; calvin cycle, C3 fixation)

Answer 28

-in some environments (arid) carbon fixation is threatened by the risk of excessive water loss -being able to keep your doors closed and windows shut during the day would be beneficial -some plants are able to take up CO2 and preform the C4 pathway at night and then carry out the Calvin cycle during the day (temporal separation) -CAM plants preform the C4 pathway at night allowing malic acid to accumulate in the vacuole -during the day these organic acids are used to supply CO2 to the Calvin cycle -CAM plants can keep their stomata closed while using stored CO2 pools for photosynthesis

Answer 29

-the temporal separation fo CO2 fixation and the Calvin cycle was first discovered in the family Crassulaceae and therefore named Crassulacean Acid Metabolism -among vascular plants, CAM is more widespread than spatial C4 fixation (about 5%) -CAM evolved independently in many succulents including cacti, pineapple, and stonecrops -not all CAM plants are succulents, some orchids, ferns, and Welwitschia (gymnosperm) -the ability to fix CO2 in the dark through the activity of PEP carboxylase in the cytosol is the defining feature of CAM plants

Answer 30

-in C4 plants, the C4 pathway and the Calvin cycle run simultaneously -the pathways are spatially separated such that the C4 pathway is carried out in mesophyll cells and the calvin cycle in bundle sheath cells (when Kranz anatomy present)

Answer 31

-CO2 is fixed at night when the stomata are open 1. starch from the chloroplast is broken down as far as PEP 2. HCO3- (bicarbonate ion) reacts with PEP to form oxaloacetate and is then reduced to malate 3. Malate is stored as malic acid in the vacuole

Answer 32

-stomata are closed 1. malic acid id recovered from the vacuole and decarboxylated producing CO2 and pyruvate 2. the CO2 enters the Calvin cycle where it is re-fixed by RubisCO 3. stomatal closure prevents loss of water and CO2 released by the decarboxylation of malate

Answer 33

1. improving light harvest by adding another photosystem and varying pigments 2. improving energy generation by maintaining potential for cyclic electron flow 3. improving CO2 fixation a) by spatially separating fixation from sugar phosphate synthesis and changing the permeability barriers surrounding some cells (C4 plants) b) by temporally separating fixation fixation from sugar phosphate synthesis and storing intermediates (starch, malic acid) for use later (CAM plants)

Answer 34

-chemicals used to modify plant development and growth -often small amounts are needed -includes both naturally occurring hormones (endogenous) and synthetic substances (exogenous) -plant response to growth regulators integrates the activity of signalling pathways

Answer 35

-growth regulators act by binding to a specific receptor, thereby initiating a series of biochemical events (response) -the response can be positive (turn something on) or negative (turn something off)

Answer 36

-concept of hormones originated from work in mammalian systems -share three basic elements: 1. synthesis in one part of the body 2. transport to another part of the body 3. induction of a chemical response to control a physiological event

Answer 37

-direct growth and development -both promote and inhibit repsonses -effects of a particular hormone depends on concentration, location, and timing -key components of plant's communication system (cell to cell or long distance) -in plants some hormones act in the same tissues where they are produced

Answer 38

1. auxins 2. cytokinins 3. gibberellins 4. abscisic acid 5. ethylene

Answer 39

-first plant hormone discovered -Darwin and his son researched it first with its response to light (phototropism) -the tip of the sheath covering the shoot (coleoptile) is critical to this response -structural formula was determined to be that of indoleacetic acid (IAA) -IAA is a modified amino acid derived from tryptophan and is the most common of natural auxins -mutants entirely lacking auxin have never been isolated, indicating it is essential to plant development and function -auxin stimulated the elongation of cells

Answer 40

-activates H+ATPase in cell membrane to pump protons into the cell wall -resulting decrease in cell wall pH activates expansin enzymes -expansins cleaves bonds between cellulose and hemicellulose weakens cell wall -this process is called the acid growth hypothesis

Answer 41

-expansins temporarily disrupt hemicellulose strands to relax tension, increase space between cellulose fibers -cell wall expansion is irreversible

Answer 42

-response of angiosperms grown with little to no light -plants attempt to reach potential light source -elongation of stem and leaves via increased auxin levels -longer internodes (fewer leaves) -chlorosis (lack of chlorophyll)

Answer 43

-short term effect is to stimulate cell elongation, but also impacts many aspects of plant development Promotes: -root-shoot axis during embryogenesis -lateral (adventitious) root formation -differentiation of procambium and dedifferentiation of vascular tissue -fruit development Inhibits: -axillary buds and secondary branching -lateral root length -abscission in young leaves and immature fruit

Answer 44

-all plant tissues are capable to synthesizing IAA -higher production in meristems, buds, young leaves, and actively growing parts of the plant -highest levels of auxin synthesized in shoot tip, maxima in leaf primordia -auxin synthesized in leaves can be transported in the sap of phloem sieve tubes (non-polar mass flow) to rest of plant

Answer 45

-in addition to transport in phloem, active polar transport occurs -polar auxin transport facilitated by IAA influx and efflux transporters -the main route of polar auxin transport in stems and leaves is through parenchyma cells surrounding vascular bundles -polar auxin transport is unidirectional

Answer 46

-IAA concentration gradient forms, with highest levels present in the shoot tip -shoot-root orientation determined by polar auxin transport as IAA moves away from source (shoot tip) towards roots due to unidirectional placement of efflux/influx transporters

Answer 47

-auxin from shoot tip suppresses axillary buds from becoming secondary (lateral) branches -removal of shoot tip (pruning), reduces auxin levels -auxin is involved in apical dominance, the suppression of axillary bud growth closest to shoot tips -removal of shoot tip releases axillary buds from apical dominance

Answer 48

-in the root, auxin from shoot moves through sieve tubes (bulk flow) in vascular cylinder to root tip (acropetal) -once at root tip, suxin is redirected to the epidermis and cortex via polar transport and back upwards to the root-shoot junction (basipetal) -in addition to polar transport from shoot, IAA also synthesized in RAM

Answer 49

-auxin promotes later root formation -accumulation of auxin in pericycle stimulates cell expansion and lateral root formation -too much auxin however will inhibit root length

Answer 50

-auxin synthesis promotes differentiation in procambium (formation of primary xylem and phloem) in shoot and root meristems -auxin transport and synthesis from surrounding cells initiates dedifferentiation of vascular tissue in formation of vascular and cork cambium in secondary growth

Answer 51

-auxin promotes fruit development through expansion and by inhibiting fruit ripening and abscission -developing seeds are a source of auxin to promote maturation of the ovary wall -parthenogenic fruit formation (fruit formed without fertilization) can be stimulated in some species by the exogenous application of auxins

Answer 52

-since the first discovery of auxin, several synthetic versions have been developed -1-naphthaleneacetic acid (NAA) has been used to induce adventitious roots in plant cuttings and reducing fruit drop (abscission) -synthetic auxins are not as readily degraded by IAA oxidase as IAA, resulting in plants treated with these growth regulators to retain artificially high levels of these compounds -the effect can be lethal depending on the dose and the plant -2,4-D first herbicide developed in 1946 -synthetic auxins are effective at selectively killing broad leave plants while allowing grass crops to survive -broad leaf plants (dicots) potentially absorb and transport synthetic auxins more rapidly than grasses (monocots) and are thus more susceptible to the downstream effects of ethylene production

Answer 53

-discovered by Johannes van overbeek in 1942 as a growth promoting factor in coconut milk -miller and skoog identified a purine compound they called kinetin and named the group of growth regulators cytokinins -zeatin is the most active of endogenous cytokinin hormones

Answer 54

-cytokinins are typically modified forms of adenine -cytokinin synthesis in actively dividing tissues of seeds, fruit, leaves, buds, and roots -high levels of cytokinin synthesized in RAM, transported up to rest of the plant through xylem

Answer 55

-delay or reverse tissue senescence (old age) by directing amino acids to locations of higher cytokinin concentrations -increase of cytokinin can reverse loss of chlorophyll in dying tissue -cytokinins promote cell division in meristems (SAM and RAM) and developing fruits -applying cytokinins to axillary buds induces cell division and promotes secondary (lateral) branching, altering apical dominance

Answer 56

-often a hormones concentration relative to other hormones determines whether or not it will have an effect on the plant (not absolute values) -relationship with other growth regulators can be synergistic (cooperative) or antagonistic (opposing) -different developmental stages and events require different hormone rations -cytokinin alone has no effect without auxin present -the ratio of auxins to cytokinins regulates the production of roots and shoots

Answer 57

-cytokinin synthesis is localized to central zone of SAM to promote cell division of totipotent cells (high cytokinin, low auxin) -derivative daughter cells in primordia and procambium are exposed to high levels of auxin to promote cell expansion and differentiation (high auxin, low cytokinin)

Answer 58

Cell division -cytokinin synthesized and transported so higher concentrations at base, cell division occurs (high cytokinin, low auxin) Expanding cells -newly formed cells expand in center of leaf; new vasculature also formed (high auxin, low cytokinin) Mature cells -cells are fully expanded; both cytokinin and auxin levels drop

Answer 59

-axillary buds produce their own auxin and cytokinins, however auxin synthesized and transported from SAM generates strong auxin gradient near shoot tip (high auxin, low cytokinin) -as shoot extends, older axillary buds move further away from the SAM and its inhibitory auxin; once cytokinin levels exceed auxin, dormant bids become active and secondary branches form (high cytokinin, low auxin)

Answer 60

-ratios vary by species -typically conifers have strong apical dominance while deciduous trees have weak apical dominance -can remove apical dominance through pruning

Answer 61

-high auxin (basipetal) promotes root hair formation in mature epidermal cells, synthesized cytokinin transported away in xylem -high auxin biosynthesis and accumulation from polar transport promotes elongation and eventual differentiation -high cytokinin biosynthesis in quiescent center of RAM promotes active division of initials

Answer 62

Forms: indole acetic acid (IAA) most common in plant; Synthetic forms include NAA and 2,4-D Biosynthesis: produced throughout entire plant, but concentrated in newly developing tissues, maxima in SAM Function: 1. Promotes cell elongation (expansins), tropic responses 2. Defines root-shoot axis in embryo 3. Promotes apical dominance and lateral root formation 4. Stimulates vascular differentiation and de-differentiation 5. Promotes fruit development and inhibits abscission Transport: polar auxin transport, phloem Relationships: antagonistic with cytokinin, synergistic with ethylene Applications: ‘weed killers’ (triggers ethylene), vegetative propagation (root cuttings, in vitro)

Answer 63

Forms: five active forms; zeatin most active Biosynthesis: adenine and phenylurea derivatives; maxima in SAM and RAM but also actively dividing tissues and root tips Function: 1. Promotes cell division in meristems (shoot and root), cambium in secondary growth and very young fruit 2. Delays and reverses leaf senescence 3. Ratio with auxin regulates root and shoot production Transport: xylem from root Relationships: antagonistic with auxin Applications: vegetative propagation (in vitro), delaying senescence

Answer 64

-In 1902, Gottlieb Haberlandt recognized the totipotency of plant cells. -Tissue culture method developed in the 1960s by culturing plant cells, tissues or organs in artificial medium containing nutrients and ratios of hormones (auxins : cytokinins) -Also known as in vitro propagation

Answer 65

1. callus forms on cut stem (undifferentiated cells) 2. meristem (primordia forms on callus) 3. shoot 4. rooting 5. plant

Answer 66

1. Clones are genetic copies of parent plant (preserve traits) 2. Speed up maturation process 3. Can generate plants from any living tissue when seeds not available or plant not viable

Answer 67

Cytokinins alone have little effect; auxin by itself promotes cell elongation * Low cytokinin to high auxin ratios give rise to roots in tissue culture * Equal cytokinin to auxin ratios give rise to undifferentiated, dividing cells (callus) * High cytokinin to low auxin ratios cause cells to divide and differentiate into axillary (shoot) buds - The effect of growth regulators, dependent on type of plant tissue used and the plant species from which the tissues originate

Answer 68

High auxin to low Auxin and Low cytokinin to high cytokinin: -rooting on shoots (primary root initiation) -rooting on callus (primary root initiation) -callus formation (undifferentiated cell division) (even levels) -adventitious buds (lateral root initiation) -axillary buds (lateral branch initiation)

Answer 69

- Discovered by Japanese scientist Kurosawa in 1926, when studying a disease in rice caused by a fungal pathogen, Gibberella fujikuroi - Infected plants were spindly, pale-coloured and sickly seedlings: “foolish seedlings” - In 1934, chemical from fungus was isolated and identified, named gibberellin (GA) - Most plants contain 10 or more GAs; to date over 136 different GAs have been isolated

Answer 70

- GAs are synthesized in apical meristems (SAM, RAM), young leaves and developing seeds - Biosynthesis not fully understood but partly takes place in plastids and inactive precursors are abundant - GA’s are transported and accumulate during key stages of development but mechanism not fully understood; xylem and phloem transport, nonpolar

Answer 71

- Promote shoot elongation * Induce floral transition and fruit development * Promote embryo development (mobilizes food reserves) * Stimulate seed germination * Accelerate plant growth: - GA’s signal transitions between meristem to shoot, young to mature leaves, and vegetative growth to flowers/reproduction - Exogenous application of GA can accelerate plant development in dicots and some monocots, no effect in conifers

Answer 72

- Exogenous application of GA stimulates stem elongation in dwarf plants - Growth effect of GA dependent on presence of auxin - GA promotes stem elongation by: 1. Enhancing expansin synthesis 2. Modifying cell wall extensibility by breaking hemicellulose (xyloglucan) strands through stimulation of xyloglucan endotransglycosylase (XET)

Answer 73

- The seeds of many plants require a period of dormancy before they will germinate - In some plants a cold period must be experienced before seeds will germinate (vernalization) while in others light is required to break dormancy - Exogenous GAs can substitute for either vernalization or light- induction for germination

Answer 74

- Gibberellins have important commercial application, although expensive - When applied to developing bunches of grapes, GAs promote elongation of stem internodes and increase grape size

Answer 75

Forms: 136 have been identified, plants typically have at least 10 different forms present; all are diterpenoid acids Biosynthesis: occurs in young, developing tissue (meristems, leaves, seeds) Function: 1. Promotes shoot elongation: modifies cell wall extensibility by enhancing expansin synthesis and inducing xyloglucan endotransglycosylase 2. Promotes embryo development and seed germination 3. Flower transition and fruit formation Transport: not fully established but nonpolar, phloem and xylem Relationships: antagonistic with ABA, synergistic with auxin Applications: increase internode length and fruit size, accelerate growth

Answer 76

- Discovered by Torsten Hemberg in 1949 who found that buds contained a growth inhibitory substance which he called “dormin” - In 1960s, Frederick Addicott found that cotton leaves and fruits contained a substance capable of accelerating abscission which he called “abscisin” - Dormin and abscisin were later shown to be chemically identical, today it is known as abscisic acid or ABA

Answer 77

- It is now known that ABA plays NO direct role in abscission; rather it stimulates ethylene production - Synthesized throughout plant, in cells that contain plastids (chloroplasts or amyloplasts) from carotenoid pigments - Transported by phloem and xylem, nonpolar - ABA plays a role in root-to-shoot signalling

Answer 78

- Under conditions of water stress (drought, salt, or freezing) roots increase ABA biosynthesis - The increased ABA is then transported up to shoot in xylem - ABA activates pumps that remove protons from guard cells, cause stomata closure - Mutants incapable of synthesizing ABA have a wilty phenotype and must be grown under conditions of high humidity

Answer 79

- ABA plays a major role in seed development 1. Stimulates the production of seed storage proteins 2. Promotes seed dormancy 3. Inhibits seed germination - Mutants that are entirely lacking in or are insensitive to ABA, fail to become dormant (for example, viviparous maize mutants germinate on mother)

Answer 80

Aliases: Dormin Biosynthesis: any cells containing chloroplasts or amyloplasts (no pigment, starch storage) Function: DOES NOT DIRECTLY CAUSE ABSCISSION 1. Promotes seed dormancy 2. Inhibits cell division and seed germination 3. Response to abiotic stress, signal closure of stomata when water limited Transport: xylem and phloem Relationships: antagonistic with GA

Answer 81

- Effects discovered before auxin - History goes back to “illuminating gas” that was used in the 1800s to light lamps on city streets - Leaks of illuminating gas caused defoliation of shade trees along streets - In 1901 Dimitry Neljobov demonstrated that the gas, ethylene, was the active component in illuminating gas

Answer 82

- Ethylene is synthesized from the amino acid, methionine, giving rise to ACC (1-aminocyclopropane-1-carboxylic acid) - ACC is converted into ethylene, CO2, and ammonium ion by enzymes of the tonoplast (vacuole) - As a gas, ethylene can be transported into intercellular air spaces and outside the plant itself

Answer 83

- Biosynthesis occurs in all plant tissues - Meristemic and nodal regions tend to be most active - Increased synthesis during leaf abscission, flower senescence and fruit ripening - ACC and subsequent ethylene can be stimulated in response to abiotic (flooding, chilling, temperature or drought), biotic (wounding, disease) and mechanical (touch) stress

Answer 84

- Ethylene promotes shedding (abscission) of leaves, flowers and fruits in many plant species; originally believed to result of ABA - Ethylene stimulate enzymes that digest cell walls in abscission zone - In many plants, abscission is controlled by interaction between auxin and ethylene - Auxin appears to decrease sensitivity of abscission zone cells to ethylene (prevents premature “fruit drop”)

Answer 85

- Ethylene induces lateral cell expansion by changing microtubule orientation (from transverse orientation to longitudinal orientation) - Shift in microtubules lead to a change in cellulose microfibril deposition

Answer 86

- Ethylene enables plants to adapt to underground obstacles by initiating a response known as the triple response - NOT the same as etiolation 1. Slowing of stem or root elongation 2. Thickening of the stem or root 3. Curving to grow horizontally

Answer 87

- Mechanical (touch) stress induces ethylene production - Early ethylene production inhibits cell elongation, inducing lateral cell expansion, stunting growth - This stunted response known as thigmomorphogenesis - Thigmotropism (when plant responds to touch) is controlled by both auxin ethylene

Answer 88

- Fruit ripening involves changes such as: degradation of chlorophyll, softening of tissue by enzymatic digestion of middle lamella and synthesis of sugars from starches, organic acids or oils - Some fruits have a large, rapid increase in ethylene production that precedes a sharp increase in cellular respiration (release of CO2) - Such fruits are known as climacteric fruits because of this peak in respiration (apples, avocados, bananas, cantaloupes, mangos, peaches, plums and tomatoes) - In nonclimacteric fruits (cherries, citrus, grapes, pineapple, and watermelon), CO2 production decreases as ripening occurs

Answer 89

- Biosynthesis: made from methionine (amino acid) using tonoplast (vacuole membrane) enzymes; found in every plant cell, increases in senescing leaves and flowers, ripening fruit and in response to abiotic, biotic and mechanical stress Function: 1. Promotes abscission of leaves, petals and fruits 2. Initiates triple response and thigmotropism 3. Promotes fruit ripening: chlorophyll degradation, tissue softening and synthesis of sugars from energy reserves Transport: intercellular air space, airborne Relationships: synergistic and antagonistic with auxin Applications: agriculture uses it to control ripening

Answer 90

- Discovered 40 years ago, these hormones act like auxin (mutants looks similar to auxin mutants) -They were first discovered in the genus Brassica and hence were named Brassinosteroids - Brassinosteroids stimulate cell division, xylem differentiation, promote pollen tube growth, low concentrations promote root growth and development, promote elongation in shoots and enhance ethylene synthesis and senescence - These compounds bind to plasma membrane receptor proteins but do not enter the cell

Answer 91

Forms: 70 BR’s have been identified Biosynthesis: made from campesterol, sites of synthesis not established but believed to occur in all plant tissues Function: “auxin-like” 1. Promotes cell division, vascular differentiation and pollen tube formation and elongation in shoots 2. Inhibits root formation at high concentrations, promotes root initiation and growth at low [ ] 3. Enhances ethylene and accelerates senescence Transport: possibly acropetal transport (phloem) Relationships: synergistic with auxin and ethylene Applications: potential in agriculture to improve stress resistance (cold and drought) and yield of crops

Answer 92

Forms: oxygenated fatty acids Biosynthesis: made from linolenic acid in peroxisome, synthesized in all cells with chloroplasts. Synthesis increases as part of wound response. Function: 1. Defence against biotic and abiotic stress; volatile signal that stimulates defence responses (ex. nicotine) in plant and neighbouring plants (interplant communication) 2. Promotes formation of lateral roots, tendril coiling, flowers, fruits and seed development 3. Promotes senescence and leaf abscission Transport: airborne, phloem Relationships: antagonistic with salicylic acid in dicots Applications: Possible anti-pest defense; methyl- jasmonate and cis-jasmone used in perfume industry

Answer 93

Polyamines * synthesized from amino acids * are highly abundant (millimolar amounts) * promote cell division, synthesis of DNA, RNA and proteins, tuber formation, root initiation and development of embryo, flower and fruit Salicylic acid * activates chemicals in pathogenic defense Strigalactones * Inhibit shoot secondary branching, synergistic with auxin

Answer 94

Light regulates many aspects of plant growth and development * Elongation and growth of tissues * Germination * Circadian rhythm * Seasonal responses and flowering * Stomata and gas exchange * Polar cell growth (differential expansion) * Chloroplast movement

Answer 95

- Plants can differentiate between different wavelengths (colour) of visible light - Different wavelengths, illicit different responses in growth and development - Specifically blue (450-495 nm) and red (650-790 nm) light is differentiated via photoreceptors

Answer 96

Red and blue light regulates many aspects of plant growth and development Red light * Elongation and growth of tissues * Germination * Circadian rhythm Red and Blue * Seasonal responses and flowering * Stomata and gas exchange Blue light * Polar cell growth (differential expansion) * Chloroplast movement

Answer 97

Three principal families of signal-transducing photoreceptors: 1. Red/Far Red (R/FR) light absorbing phytochrome (PHY) 2. UV-A/Blue light absorbing cryptochromes (CRY) 3. Blue light absorbing phototropins (PHOT) - Function of individual photoreceptors can be difficult to differentiate due to redundancy and synergistic mechanisms. - For example, reversal of etiolation (de-etiolation) is believed to involve all three photoreceptor families in detection and response to light

Answer 98

- Photomorphogenesis is light mediated development, where plant growth patterns respond to light - PHY and CRY photoreceptors primarily used in photomorphogenesis

Answer 99

Phytochromes (PHY) are a family of five photoreceptors that respond to red and far-red light (infrared) * Exposure of phytochrome to red light (660nm) converts it to a form (P FR) that absorbs far-red light (720nm) * Exposure of PFR to far-red light, converts it back to the form that absorbs red light (P R) * Acts like an on/off switch, generally, P FR=ON and P R=OFF * Cause short and long-term effects which are carried out by signal transduction pathways

Answer 100

Photodormancy (requirement of seeds for light or dark conditions for germination), can be overcome by: 1. Exposure to red (“sun-loving”) or far-red light (“shade-loving”): in most angiosperms, high P FR: low P R ratios required for germination 2. Gibberellins 3. Cold treatments (vernalization) 4. By removing the seed coat and endosperm to expose the embryo (stratification)

Answer 101

- Plants, like many organisms, have biological cycles of about 24 hours - These regular, approximately 24 hour cycles, are called circadian rhythms (from Latin circa, “approximately” and dies, “a day”) - These rhythms are internal and mediated by ‘biological clocks’ Many plant processes follow a 24 hour cycle * Leaf and flower opening and closing * Volatile emissions (floral scents) * Photosynthesis * Auxin synthesis * Gene expression

Answer 102

- Are ‘entrained’ or reset by the natural cycle of day/night - Plants can sense the relative length of night and day (photoperiod) - Phytochromes measure day length by changing from active form (P FR) to an inactive form (P R) in the dark - Phytochromes control seasonal and circadian rhythms (24hr) by turning genes off and on

Answer 103

- In response to changes in photoperiods plants can alter their development and switch to flower production * Some plants flower when day length becomes short (short-day plants, SDP) or longer nights * Some plants flower when day length become long (long-day plants, LDP) or shorter nights * Others are unaffected by day length and are therefore day-neutral - In 1940’s, it was determined that night-length, not day-length, was critical to flowering photoperiod

Answer 104

- SDP flower when the night exceeds a critical length - LDP plants flower when the night is shorter than a critical length - Flash of red-light at night reverses the response, disrupting critical length - Presence of P FR disrupts photoperiod - Phytochromes are produced in leaves in the chromoplasts. How does red light signal in leaves reach SAM to induce flowering? - A flowering hormone (florigen; FT) was theorized and in some species (grasses) it has now been identified as a gibberellin - Grafting experiments demonstrated that the signal is transmissible through the phloem - Experiments with leaf covering and artificial photoperiods also supported mobile signal

Answer 105

- P FR:PR can only be used to measure day length - The nature of the cellular component that measures night length is not fully known * P FR levels do not last through the night, decay back to P R(dark reversion) * It is thought that a subpopulation of phytochrome molecules may be involved in measuring night length * Increasing evidence from study of bud formation suggests phytochromes double as temperature sensors at night-time

Answer 106

(A) A SD plant (cocklebur) exposed to long days did not flower (B) Flowering was induced when one leaf of the same plant was exposed to SD conditions

Answer 107

- PHY (red light) and CRY (UV- Blue light) photoreceptors activate genes, inducing signal transduction pathway in leaves - Florigen mRNA is synthesized and FT protein is transported to the SAM via the phloem - In the SAM, FT protein acts together with a transcription factor, FD, to activate genes involved in floral development

Answer 108

A tropism is the growth response involving bending or curving of a plant towards or away from an external stimulus that determines the direction of movement Tropic growth occurs in response to: * Light = phototropism * Gravity = geotropism * Touch = thigmotropism

Answer 109

- In phototropism, the plant grows towards or away from light - Growth towards light is known as positive phototropism (shoots) - Growth away from light is known as negative phototropism (roots) - Light affects auxin distribution; hormone moves away from light, accumulates on shaded side of tissue - Light does not cause auxin degradation but rather change in distribution

Answer 110

- In shoots, accumulation of auxin promotes cell elongation, thus shaded cells grow longer - Shaded side, high auxin - Sun exposed side, low auxin

Answer 111

- In roots, high auxin (shade) inhibits cell expansion therefore the dark side of the root grows less; helps root move away from light - sun exposed side, low auxin - shaded side, high auxin

Answer 112

Phototropism (auxin) responsive to blue and, less so, green light

Answer 113

- Research in the 1980s identified two plasma membrane proteins that exhibited blue light induced phosphorylation, but bioassays failed at isolating them - Studies using Arabidopsis mutants to screen for loss of function (impaired phototropic responses) led to the identification of these two mystery membrane proteins: PHOT1 and PHOT2 - PHOT1 and PHOT2 are light receptors that absorb blue light, autophosphorylate, and initiate a signal transduction cascade that results in auxin redistributing to the shaded side of the tissue - Study of phot1 showed that loss of PHOT1 impaired phototropism in dim blue light; lack of PHOT2 in phot2 had no discernible effect - Study of individual mutants suggested functional redundancy between the two light receptors - Double mutants phot1phot2 (complete loss of PHOT1/2) had impaired leaf expansion (not shown here) and exhibited no phototropic response, chloroplast migration or stomata opening

Answer 114

- Double phot1phot2 Arabidopsis mutants exhibit impaired leaf expansion - PHOT proteins (and blue light) potentially regulate distribution of auxin in young leaves

Answer 115

- PHOT1 and PHOT2 in guard cell plasma membrane absorb blue light, signalling the export of protons with H+ATPase - Negative electric potential created by pumping out protons, drives K+ to enter guard cell through K+ channels - Blue light believed to be the “first crack of dawn signal” after stomata closed at night; not dependent on photosynthesis Open Stomata (K+ pumped in) * PHOT1 and PHOT2 absorption of blue light, independent of photosynthesis * PHYTB absorption of red light in chloroplasts of mesophyll and guard cells, believed to be link between photosynthesis and decreased CO2 signal Closed Stomata (K+ pumped out) * No light * Decreased turgor pressure (low water) * ABA signal from roots CAM Stomata - Open at night, not controlled by light receptors... Mechanism not known, but believed to be entrained clock/degradation of signal

Answer 116

Accumulation response: low light response where chloroplasts distribute uniformly to maximize light capture Avoidance response: high light response where chloroplasts redistribute to minimize light exposure

Answer 117

Accumulation response: low blue light response where chloroplasts distribute uniformly to maximize light capture Avoidance response: high blue light response where chloroplasts redistribute to minimize light exposure

Answer 118

- Chloroplast migration is reversible and occurs within hours - Mediated by actin filaments. Remember cytoplasmic streaming? Similar mechanism but not continuous movement - Interaction between PHOT receptors and myosin not fully known, but PHOT2 has been documented to localize in chloroplast membrane during avoidance response

Answer 119

- Photodamage (photoinhibition) is light-induced reduction in photosynthetic capacity - Occurs in all oxygen evolving phototrophs - Exact mechanism is unknown (most likely reactive oxygen species) but do know that PSII is most affected and blue/UV light cause the most damage

Answer 120

Positive gravitropism: Roots grow toward gravity Negative gravitropism: Shoots grow away from gravity

Answer 121

Three current hypotheses attempt to explain how plants sense and respond to gravity 1. Starch-statolith hypothesis 2. Protoplast pressure hypothesis (gravitational pressure hypothesis) 3. Tensegrity model (“tensional integrity”)

Answer 122

- Proposes that sedimenting amyloplasts play the role of statoliths (gravity sensors) - Amyloplasts are non-pigmented plastids that synthesize/store starch from glucose - In the shoot, specialized cells containing amyloplasts surround vascular tissues (starch sheath) - In the root, amyloplast containing cells are in the root cap

Answer 123

This hypothesis proposes that the weight of the entire mass of the protoplast (entire cell excluding cell wall) is involved in gravity perception

Answer 124

This hypothesis proposes that amyloplast sedimentation disrupts the actin filaments causing transient influx of calcium signal

Answer 125

- Following gravity perception, auxin efflux carrier proteins (PIN3) are re-distributed in plasma membrane; polar auxin transport is concentrated on the lower side of root - Once +ve gravitropism has been re-established: PIN3 and auxin are once again equally distributed in root tip

Answer 126

- Growth in response to touch Thigmotropism can be achieved by: 1. Turgor pressure 2. Hormonal signalling (ethylene & auxin) - Rapid plant responses to touch, as seen in “sensitive plants”, Mimosa pudica, are achieved by turgor pressure - In climbing plants, thigmotropsism allows the plant to gain better access to light and support - Tendrils use auxin to extend and reach objects and ethylene to wrap around objects

Answer 127

- Leaf movement results from changes in turgor pressure of pulvini (special parenchyma cells at the base of leaf) - Pressure on mechanoreceptors signal interior pulvinus cells to pump ions out (Ca 2+ , K+ , Cl- ); water diffuses out of cell - A similar mechanism regulates closing of a Venus fly trap in response to insect activity - Stimulation of receptor cells depolarizes the membrane causing hinge mesophyll cells to take up water

Answer 128

- Tendrils synthesize ethylene on the side that contacts the object (touch): expansion inhibited, width increased - Side with no contact is unaffected (no ethylene); expansion not impaired

Answer 129

- Photoinhibition damage and repair is always occurring, even under optimal conditions - Becomes a problem when plant is exposed to extended environmental stress: sustained high light, high temperature, and drought

Answer 130

- Chloroplasts have ROS-eliminating systems, can repair nucleic acids, re-synthesize lipids and proteins, and quench excited chloroplasts to reduce effect of photoinhibition - Plants have also developed strategies to reduce the risk of photodamage occurring - One strategy is to reduce amount of light reaching the chloroplast and PS reaction centres

Answer 131

- Carotenoids: stored in plastids, accessory pigments in photosystems to dissipitate light energy -β-Carotene (orange) -Xanthophyll (yellow) Anthocyanin: flavonoids stored in vacuole, are blue, purple or red depending on pH - Can be used to attract pollinators in flowers and protect plant from biotic and abiotic stress

Answer 132

Phenolic acids are found in all plant organs, and stored in the vacuole. * Protect plant from both UV light and predators (more on that later) * Can accumulate in cuticle and epidermis Flavonoids (polyphenols) are stored in the vacuole and include: Anthoxanthin (white or yellow) * Important in UV filtration Anthocyanin (red, purple or blue depending on pH) * Absorb visible light (blue-green) as a pigment * Capture free radicals, including ROS * Accumulation induced by light, temperature and jasmonic acid

Answer 133

- Decrease in water decreases rate of photosynthesis as PSII and photolysis requires water, results in plants absorbing more light energy than can be consumed. Thus in addition to blocking excess light, conserving water also important. Several strategies include: * CAM photosynthesis * Succulent leaves (water storage) * Thickened cuticles

Answer 134

- Plants provide food for many animal and insect species and suffer diseases caused by microbial pathogens - Secondary metabolites/natural products (alkaloids, phenolics and terpenoids) defend against both herbivores and microbial pathogens such as bacteria and fungi - It has been suggested that these secondary compounds evolved primarily to protect against photodamage and climate changes

Answer 135

Disease-causing organisms elicit complex responses Infection by fungi, bacteria or viruses induce (i) local/cellular or (ii) systemic responses (i) Local elicit response: 1. Pathogen molecules (elicitors) bind to receptors in the plasma membrane leading to a localized reaction called a hypersensitive response (HR) 2. HR limits the spread of infection by causing localized cell death and producing antimicrobial compounds 3. The localized cell death is ‘programmed’ and results in a noticeable lesion on the leaf at the site of infection - During local response, dying cells release salicylic acid (aspirin precursor; phenolic acid) and nitric oxide (NO) which initiate a (ii) systemic response (whole plant response) - The systemic response (systemic acquired resistance or SAR) leads to the production of compounds that attenuate pathogen growth and increase the levels of resistance of the whole organism (similar to our innate immunity)

Answer 136

- Herbivore and ozone damage results in the production of ethylene - Ethylene perception reduces the production of pathogen defence compounds, inducing other defence genes and stimulating the production of jasmonic acid (volatile) and volatile organics (green leaf volatiles) - Damaged plant tissue releases products derived from the breakdown of fatty acids (jasmonic acid, methyl jasmonate and green leaf volatiles) act as signals that can be perceived by other plants (and other organisms)

Answer 137

- To date a total of more than 1700 volatile compounds have been isolated from >90 plant families - Plant volatiles constitute about 1% of plant secondary metabolites (organic compounds not directly involved in normal growth or development) - These compounds are released into the atmosphere from leaves, flowers and fruits and into the soil from roots - Volatiles include fatty acid derivatives and amino acid derivatives - Volatiles are typically lipophilic (“fat loving”) liquids with high vapor pressures - Typically synthesized in the epidermis and can cross membranes freely (signal) - Plant receptors that detect volatiles have not yet been identified, however, a strong Ca2+ -dependent membrane depolarization occurs at the site of herbivore damage - Mechanical damage alone induces depolarization and kinase activation but no Ca2+ influx - Ethylene biosynthesis is induced in response to herbivory, mechanical damage and exposure to herbivore induced volatiles

Answer 138

- Plants can attract natural predators (wasps, mites) of attacking herbivores using volatiles: tritrophic interactions - Attracted predators use herbivore as parasitic hosts for their larvae

Answer 139

- Biotechnology is utilizing living cells and cellular materials to create pharmaceutical, diagnostic, agricultural, environmental and other products to benefit society - Secondary metabolites, substances manufactured by plants that make them competitive in their own environment, have many pharmaceutical applications Significant pharmaceutical plant products include: 1. Phenolics 2. Alkaloids 3. Terpenoids

Answer 140

- Phenolics are antimicrobial, antiseptic (can be applied to living tissue to prevent infections) and can be herbivore deterrents (taste) - Salicylic Acid: colourless and bitter tasting, it is a precursor to Aspirin (anti-inflammatory, pain reliever). Also serves as signal in pathogenic systemic response. - Cannabinoids: synthesized in trichomes of cannaboids, psychoactive effect in animals (not insects) - Capsaicins: concentrated in placental tissue of chili pepper seeds, chemical irritant (spicy!) and neurotoxin in mammals. Birds are immune to ill-effects, aide in seed dispersal (do not chew or digest the seeds) - Raspberry Ketones: source of red raspberry smell (perfume, cosmetics) - Methyl salicylate: component of essential oil Wintergreen

Answer 141

- Alkaloids are derived from amino acids and range in biochemical effect: inhibit protein synthesis, DNA repair, weaken cell membranes or affect nerve transmission. All have bitter taste. - Nicotine: psychoactive stimulant found in nightshades, functions as insecticide (now banned for that use) - Caffeine: psychoactive stimulant, most commonly isolate from Coffea seeds but found in other plant species - Morphine: pain medication, component of opium (latex) - Cocaine: central nervous system stimulant found in Coca leaves - Strychnine: highly toxic to animals (“rat poison”), common source seeds of Strychnos tree - Quinine: treatment for malaria, first isolated from Cinchona bark

Answer 142

- Diverse aromatic (volatile) compounds derived from isopropene. - Over 10,000 known terpenoids (60% of known natural products) include: - Menthol: essential oil commonly isolated from peppermint leaves, local anesthetic - Artemisinin: highly effective anti-malaria drug isolated from sweet wormwood - Taxol: anti-cancer drug isolated from bark of Pacific yew, disrupts microtubules of dividing cells

Answer 143

- Tissue damage (herbivory) synthesizes ethylene which initiates volatile jasmonic acid signalling pathways and green leaf volatile (GLV) emission - Herbivore-infested plants can signal intact leaves on the same plant or neighbouring plants to launch defence responses - Defence response include inducing the expression of genes and the emission of volatiles

Answer 144

- Include fatty-acid derived aldehydes, esters and alcohols - Found in nearly all green plants, they are quickly produced - Have antimicrobial properties to prevent infection at sight of injury - Bacteria and fungus produce their own volatiles that can be detected by plant and initiate response - Can also promote salicylic acid (SAR signal), which is antagonistic to jasmonic acid (herbivore response)... cross- talk between hormones and GLV likely determine pathogen or herbivore response

Answer 145

- Volatiles act as pheromones to attract pollinators - Floral scents may be composed of up to 100 different volatiles, no two floral scents are the same - Floral scents allow pollinators to discriminate between flowers among species and even within a species - Among primitive land plants (mosses and ferns) volatiles are expressed constitutively - In angiosperms, rate of scent emission can vary as a function of time of day, flower age, temperature, moisture and pollination status

Answer 146

- “The transfer of genetic information from one organism to another” - This definition includes: - Traditional breeding strategies where individuals from the same species or closely related species sexually reproduce. - The incorporation of foreign DNA into the genome of a different species by recombinant DNA technology (biotechnology).

Answer 147

- Traditional breeding, brings genomes together through cross fertilization, then selecting for desirable traits - Cross fertilization can be performed on self-pollinating (wheat, rice, barley, beans and tomato) and cross-pollinating (corn, rye and most fruits and vegetables) plants - Traditional breeding between self-pollinating species is time consuming, as need to remove male reproductive structures before pollination can occur - Offspring of cross fertilization are hybrids - Outcrossing (crossing between genetically different plants) often results in hybrid vigor (heterosis), in which offspring are more productive than the parents - In early corn studies (1908), crop yield increased 4-fold in hybrid offspring, today most corn crops in North America are hybrids - Heirloom varieties are open-pollinated populations: mixture of genotypes but more potential in surviving environmental adversity

Answer 148

- A global initiative between the 1940’s-1980’s to increase crop yields and agricultural production - Approach included distribution of hybrid seeds, synthetic fertilizers and pesticides along with modernized irrigation, equipment and management - Norman Borlaug, “The Father of the Green Revolution” was awarded Nobel Peace Prize in 1970 for his work on creating a high producing wheat hybrid using Japanese dwarf varieties: increased wheat yield 4-fold in Mexico, India and Pakistan - In 1961 “The Father of Hybrid Rice” Yuan Longping identified male sterile rice plants that could be outcrossed to produce vigorous hybrids - In the 1960’s, Ford and Rockefeller Institutes along with the Government of the Republic of the Philippines formed the International Rice Research Institute (IRRI) - Based on Longping’s work, IRRI developed the semi-dwarf rice hybrid IR8 (deficient in gibberllic acid) increasing rice production 10-fold in the Philippines and India - The Green Revolution saved millions of lives, but it also came at great environmental cost (increased fertilizer, pesticide and herbicide use) - With climate change, need another Green Revolution

Answer 149

- A vector is an agent (bacterial plasmid or viral) that can transmit a gene from one organism to another - Vectors are naturally occurring biological entities that have been altered or “engineered” to allow targeted introduction of DNA or specific genes (of interest) into host organism - In 1973, a biologically functional plasmid was constructed in vitro, marking the beginning of recombinant DNA technology

Answer 150

- If a cell does not recognize and incorporate foreign DNA, it will not be replicated and will be lost when cells divide - Bacterial plasmids and viruses are parasitic genomes that contain “replication instructions” that tell host machinery how make copies or integrate it into the genome - How vectors can permeate a host plant cell: 1. Chemical treatment to facilitate DNA uptake 2. Physical projectiles and injections 3. Biological plant pathogens can be re-purposed

Answer 151

- Cell walls can be digested with enzymes to release protoplasts from cell walls, maintained in appropriate osmoticum - Chemical treatment with polyethylene glycol (PEG) disrupts protoplast plasma membrane, allows for uptake up of plasmids

Answer 152

Pros: * Fast (view results next day) * Can use “naked DNA;” just recombinant plasmid * Can perform in a wide variety of plant species Cons: * Transient gene expression (does not integrate), not for establishing stable, transgenic lines

Answer 153

- Recombinant plasmids can be micro-injected into protoplasts - Microcarriers (gold or tungsten) are coated with recombinant plasmid and “shot” into plant tissue using gene gun apparatus

Answer 154

Pros: * Fast, view results next day * Can use “naked” DNA (plasmid) Cons: * Not feasible in all plant species or tissue, onion epidermis most commonly used * Transient gene expression (does not integrate), not for establishing stable, transgenic lines

Answer 155

- Plant pathogen research has revealed useful information about how they cause disease, including how they introduce their DNA into the host - Researchers can smuggle in genes of interest within “disarmed” pathogen genomes - Viruses introduce their genomes into the plant cell can spread systemically throughout the plant - Can replace pathogen DNA with gene of interest, does not typically integrate into plant genome - Agrobacterium tumefaciens is a soil bacterium and plant pathogen - This bacterium causes ‘crown gall disease’ and does so by infecting a plant with with tumour inducing (Ti) plasmid - Once inside the plant cell, the T-DNA becomes integrated into the plant genome where it will be replicated during cell division

Answer 156

- Genetic material between left (LB) and right border (RB) gets integrated into plant genome. - No Crown gall! Bacteria’s T-DNA has been removed. - Insertion sites in plant genome are random, and can occur multiple times - Can also generate mutant libraries to study loss of function

Answer 157

Pros: * High success rate of integration using Agrobacterium Ti plasmid * Fast (3-5 days) Cons: * Not possible in all plant species, commonly performed in tobacco to test efficacy of recombinant Ti plasmid

Answer 158

Pros: - Ti plasmid integrates into plant genome, can obtain transgenic lines through in vitro propagation Cons: - Low success rate, but can use herbicide resistance to select for successful integration

Answer 159

- While the potential for recombinant DNA technology and genetically modified organisms (GMO) feels endless, the majority of GMO’s on the market for human consumption fall into 2 categories: 1) Insecticide synthesis 2) Herbicide resistance - Separate approvals needed for human and animal consumption (animal feed)

Answer 160

- Transgenic plants are given gene for Bacillus thuringiensis endotoxin synthesis; provide plant with insecticide - First introduced to corn in 1996, but now in potato, cotton, corn, sweet potato, tomato and rice - Crops do not need to be sprayed with insecticide, however: * Concern with effect on helpful pollinator and insect species and on the food web * Insects can develop resistance

Answer 161

- Resistance to Roundup (glyphosate, Monsanto) allows farmers to reduce herbicide usage - Farmers do not need to till the fields prior to planting, rather can plant directly, reducing soil erosion - Yields are higher and costs are lower - However, still using potentially hazardous chemicals (herbicide, fertilizer) and concern with biological containment

Answer 162

- Stable integration of a foreign gene into the host cell’s genome means that all cells that arise from that transgenic cell will contain the foreign DNA - Loss of recombinant DNA is low, however “escape” of DNA possible through cross-pollination and scattering of seeds - Concern with selectable markers such as antibiotic and herbicide resistance used in creating transgenic lines getting into wild populations - Need to minimize the development of resistance to bioengineered herbicides and pesticides

Answer 163

- Reduction in available germplasm; monoculture crops are susceptible to novel biotic/abiotic stresses - Elimination of the ‘family farm’; high costs due to patents on seed stock and lack of ownership on product - Monopoly of large corporations and enforcement of propitiatory ownership of seed stocks - Potential for introducing allergins - General concern with consuming ‘foreign DNA’ - 19 of 27 European Union countries have voted to ban or partially ban GMO’s for human consumption

Answer 164

- Biopharmaceuticals are drug products manufactured in or extracted from biological sources - Vaccines, recombinant proteins (e.g. insulin), gene therapy, blood and living cells are all biopharmaceuticals - Traditionally proteins were extracted directly from animals and vaccines were made from inoculating animals - As of 2014, half of all expression systems are mammalian cell lines and 34% bacterial and 13% are yeast

Answer 165

Pros: - High yield and proper post- translational modifications (high accuracy in protein folding and glycoslation) Cons: - Expensive maintenance and set up costs, high rates of contamination and stable lines can take years to develop -mRNA vaccines have sped up development (years vs. months) but production is still rate limiting step and a finite resource

Answer 166

- Using plants as expression systems to produce biopharmaceuticals has many advantages: * Cheap set up and propagation * High yield, industrial scale possible * Fast (months versus years) * Proteins can be synthesized in different compartments * No risk of culture contamination and mammalian viruses

Answer 167

- High yields of recombinant proteins can be obtained by transforming chloroplasts with expression vectors - Bioencapsulation of proteins by plastid protects them from cytosolic and enzymatic degradation in plant cell

Answer 168

- Another potential benefit of plant expression systems is storage - Localizing recombinant protein to seeds increases storability (3 years), heat resistance (55°C ) and concentration - Lyophilisation (freeze-drying) of transgenic leaf tissue increases storability (6 months) and dosage

Answer 169

- Quantity and quality: how much is produced and is it functional, stable and free from contaminants * Purification the major cost factor in production * Despite being eukaryotes, plant and mammalian systems can vary in post-translational modification (glycosylation, disulfide bonds, protein folding)

Answer 170

- Rice is the main food source for the majority of the world’s population but a low source of vitamin A and iron - Golden Rice is genetically engineered to produce β-carotene in endosperm; created by collaborative, global initiative (including IRRI) for non-profit distribution in 2000. Golden Rice 2 (2005) produces 23x more β-carotene than original. - Has been slow to enter global market due to regulations and opposition; critics site safety, efficacy and need for food diversity - In 2019 approved in the Philippines, mass production began in 2022. 1/6 of Filipino children (6-59 months) are vitamin A deficient (2021)