crop sci le 2 Flashcards
- In photosynthesis, it was seen that energy from the light reaction was used in the dark or Calvin reaction in producing the glucose
- In organisms, glucose is utilized in the presence of oxygen and broken down to carbon dioxide, water and energy. This is achieved through the process of respiration
Respiration is the apparent opposite of PS but there are salient differences in the 2 processes
- give the formula for photosynthesis and aerobic respiration
PS:
6co2+6h2o+energy (energy in) => c6h12o6+6o2
RS:
c6h12o6+6o2 (oxidation)=> 6co2+6h2o+energy (energy out)
- Respiration is also called dark respiration–The enzymatic breakdown of glucose in the presence of oxygen to produce cellular energy or ATP
- The main product of respiration is ATP, the energy currency that is required for cellular and metabolic processes in the plant
- Not the same as photorespiration!!!
- Dark respiration also occurs in the LIGHT!!
THREE Stages of Dark Respiration
- Glycolysis
- Kreb’s cycle, also known as:
a) Tricarboxylic acid cycle
b) Citric acid cycle - Electron transport system (ETS)
glycolysis
- starting materials
- products
- Glucose from photosynthesis and breakdown/ conversion of sugars; H2O
- Pyruvate or pyruvic acid; ATP (by substrate-level phosphorylation)
kreb’s cycle
- starting materials
- products
- Pyruvic acid
- CO2; NADH2 and FADH; ATP (by substrate-level phosphorylation)
electron transport chain
- starting materials
- products
- NADH2 and FADH
- ATP by oxidative phosphorylation
Energy yield for the complete oxidation of 1
glucose molecule
theoretical yield; 36-38 atp
more realistic yield; 30 atp
one of the two component of respiration
- Gross photosynthesis (P)
- Energy for converting products of photosynthesis into plant material
- k varies: 0.12 and 0.45 with plant species and plant tissues
- Rg as the source of energy
Growth Respiration (Rg)
one of the two component of respiration
- Dry mass (W)
- Energy comes protein breakdown and respiratory processes to produce CO2
- (Rm) is for Cellular functionality
Maintenance Respiration (Rm)
formulas including the two component of respiration
- k and c are coefficents for _____ respectively
R = Rg + Rm
R = kP + cW
- photosynthesis and weight
Factors That Increase Respiration Rates
- _____
- More active, younger, higher moisture content, damaged - _____
- _____
- Limited levels (hypoxia)
- Absence (anoxia)
- - Flooding is detrimental to plants due to loss of respiration - _____
- Feedback inhibition
- Accumulation of product inhibits the forward reaction
- - Storage under high CO2 decreases respiration and increases shelf life
- Age and nature of tissues
- Higher Temperature
- Increased availability of Oxygen
- Decreased levels of carbon dioxide
- Process where water moves in liquid form in plants, and
released in vapor form through aerial parts, but mostly in
leaves, to the atmosphere - Energy dependent process
- The transformation of liquid to gas phase involves use of
energy - 97-99.5% of water taken up is lost in transpiration
- formula conversion of h2o from liquid to gas
Importance of Transpiration
1. Keeps cells hydrated
2. Maintains favorable turgor pressure for the transport of nutrients absorbed by the roots from the soil
3. Cools the plant
– heat load is dissipated in the process due to the high heat of vaporization of water
– If transpiration is extremely high 🡪 dehydration and desiccation 🡪 death
*** daily water loss
–– large, well-aerated, tropical plant: 500 L
–– corn plant : 3-4 L day-1 (99% of the water absorbed by a corn plant) during its growing season is lost in transpiration)
–– tree-size desert cactus loses less than 25 mL day-1
Types of Transpiration
Based on the avenue of exit of water vapor
- Cuticular transpiration
❑ Loss of water through cuticle
❑5-10% of the water loss
❑Lenticular transpiration
- Lenticels - pores in the outer layer of a woody plant stem
❑In deciduous species (trees which sheds off leaves) and in some fruits, water
loss through lenticels may be quite substantial.
- Stomatal transpiration
❑Through the stomata
❑As much as 90% of the water lost from plants.
What affects diffusion of water from leaf to
atmosphere?
- Relative humidity (RH) (%)
❖actual water vapor in the air: water vapor pressure in leaf
❖In leaves 100% RH; in atmosphere, RH rarely exceeds 90%
❖water diffuses out from the plants to the atmosphere
- Vapor pressure deficit (VPD) (pascal (Pa))
❖Actual water vapor pressure - water vapor pressure at saturation at the same temperature
❖when VPD is 0 Pa (i.e. when RH of the atmosphere is 100%), there is no net
movement of water
❖when the RH of the atmosphere is low, the VPD is high, and the rate of transpiration is faster
Soil-Plant-Air Continuum of Water
1. Movement of water from the soil to the root xylem
a. Extracellular or apoplastic route - water moves through non-living parts,
- e.g. capillary spaces of the cell walls and intercellular spaces
b. Intracellular route
1) symplastic pathway - plasmodesmata
2) transmembrane or transcellular pathway - vacuolar membrane (tonoplast) and the plasma membranes
2 . Movement of water from root xylem to leaf xylem
- transpiration-cohesion-adhesion theory
3. Movement of water from leaf xylem to the air
- influenced by RH and VPD
- Towards lower water potential (Ψ; expressed in megaPascal, MPa)
Movement of water from root xylem to
leaf xylem
The transpiration cohesion-adhesion theory
- water vapor leaves the air spaces of the plant via the stomates
- this water is replaced by evaporation of the thin layer of water that clings to the mesophyll cells
- tension (pulling) on the water in the xylem gently pulls the water toward the direction of water loss
- the cohesion of water is strong enough to transmit this pulling force all the way down to the roots
- adhesion of water to the cell wall also aids in resisting gravity
Factors that Affect Transpiration
I. Plant Factors
1. Efficiency of evaporative surface
2. Efficiency of water absorption.
3. Other surface/stomatal modifications
4. Phytohormones
5. Canopy structure.
II. Environmental Factors
1. Edaphic (soil) factors
2. Atmospheric factors
* Light
* Relative humidity
* Temperature
* Wind velocity
* Oxygen and carbon dioxide concentrations
How Plant and Environmental Factors Affect
Transpiration
* Leaf number: more leaves, more transpiration
* Number, size, position of stomata: more and large, more transpiration, under leaf, less transpiration
* Cuticle: waxy cuticle, less evaporation from leaf surface
* Light: more gas exchange as stomata are open
* Temperature: high temperature, more evaporation, more diffusion
* Humidity: high humidity, less transpiration
* Wind: more wind, more transpiration
* Water availability: less water in soil, less transpiration (e.g. in winter, plants lose leaves)
If TRANSPIRATION is the transport of water and nutrients from soil thru roots and xylem, then
TRANSLOCATION is the movement of assimilates (sugars and other chemicals) from the leaf through the phloem to other areas for storage, utilization and consumption by the plant
Why need a transport system
in plants?
- so that cells deep within the plant tissues can
receive the nutrients they need for cell processes - In fact:
- roots can obtain water, but not sugar,
- leaves can produce sugar, but can’t get water from the air
- Sugars required for metabolism
– all the time, in all tissues - Sugars produced only
– by source tissues
– in light period - Translocation occurs
– source to sink over short term
– from storage tissues to young tissues over long term
Sucrose
* is principal photosynthetic product
– accounts for most of CO2 absorbed
– Glucose, as initial product of photosynthesis, is converted to sucrose which is the major form for transport or translocation
* important storage sugar
– tap root of carrots and sugar beet (up to 20% dry weight)
– and in leaves, eg 25% leaf dry weight in ivy
* major form for translocation of carbon
– from photosynthetic leaves (source leaves)
– in germinating seedlings after starch or lipid breakdown
Direction of translocation:
- From Source: a part of the plant that releases sucrose to the phloem e.g. leaf
- To Sink: a part of the plant that removes sucrose from the phloem e.g. root
- A plant part can act as source or sink depending on its developmental stage: for example- young leaves act as sink, but later their predominant role would be as source, once they are active in photosynthesis
ALLOCATION
* The channelling of fixed carbon into various metabolic pathways within an organ or tissue
* In a source organ:
– Metabolic utilization within the chloroplast
– Synthesis of starch within the chloroplasts
– Synthesis of sucrose for export to sink
* In a sink organ
– Metabolic utilization and growth processes
– Storage
PARTITIONING
* DISTRIBUTION of assimilates to competing sinks
– Lower mature leaves feed mainly the roots
– Higher mature leaves feed mainly the young leaves and shoot apex
* SOURCE LEAVES
– Preferentially supply sink organs with which they have vascular connection
* Flower or fruit nearest to them (directly above or below them)
- Basis for flower and fruit thinning
Mechanism of translocation of photosynthates
1. Mass or bulk flow (Münch pressure flow hypothesis)
2. Diffusion- slow
3. Cytoplasmic streaming- within the cytoplasm through plasmodesmatal connections between cells
4. Others
1. Facilitated diffusion
2. Active transport across membranes
Mechanism of assimilate translocation:
The Münch pressure flow hypothesis of assimilate transport from source to sink
xylem (vessel) - for transpiration of water
phloem (sieve tube) - for translocation of source, transportation of products of photosynthesis (sugar) thru translocation
APOPLAST PATHWAY
* sucrose is loaded into the phloem with the help of active transport. A sucrose transporter protein is used to co-transport H+ and sucrose across the cell membrane.
* the apoplast path utilizes ATP to pump H+ against the concentration gradient.
* ATP is reduced to ADP+Pi which expels energy that enable H+ to be pushed against the gradient.
* The H+ proton that is pumped against the gradient is then used by the sucrose transporter protein to move sucrose through the membrane.
* The sucrose accumulated in the companion cell is able to flow down its concentration
gradient via the plasmodesmata and into the phloem.
SYMPLAST PATHWAY
* sucrose travels in the plasmodesmata which are connections between cells.
* Therefore, the sucrose is able to flow down the sucrose concentration gradient into the phloem which has a lot of concentration of sucrose.
Plants are:
✔ Capable of making all necessary organic compounds from inorganic compounds and elements in the environment (autotrophic)
✔ Supplied with all the carbon, hydrogen, and oxygen they could ever need (CO2, H2O)
✔ Required to obtain all other elements from the soil so in a sense plants act as soil miners.
Nutrient
* any substance that can be metabolized by an
organism to give energy and build tissue
* growth and development
* source of nourishment, especially a nourishing
ingredient in a food
* providing nourishment
Categories of Plant Nutrients
* Based on Function
❖Essential
❖Beneficial
* Based on amount required by crop
❖Macroelements
❖Microelements
* Based on capability to move from one part of the plant to another
❖Mobile
❖Immobile
CRITERIA OF ESSENTIALITY
1. If the nutrient is absent, then the plant is unable to complete its life cycle
2. The function of the nutrient must not be replaceable by another element
3. The nutrient must act directly in the metabolism of the plant
Functions of the Essential Elements
▪Structural
- important components of biomolecules (e.g. N, P, Ca, Mg, S)
▪Catalytic
- as co-factor of enzymes (e.g. most micronutrients)
▪Osmotic
- regulation of cellular hydration (e.g. K)
The Essential Nutrients
▪ Macronutrients:
- Nitrogen, phosphorus, potassium, calcium, sulfur, magnesium, oxygen, carbon, hydrogen
▪ Micronutrients:
- Iron, boron, copper, zinc, manganese, molybdenum, chloride
Macroelements/Macronutrients
- Required in relatively large quantities like one to 10 milligram per gram of dry matter
- Carbon, Hydrogen, Oxygen, Phosphorous, Potassium, Calcium and, Nitrogen, Sulphur
Microelements/Micronutrients
- Required in minute quantities like 0.1 mg per gram of dry matter
- Manganese, Boron, Copper, Molybdenum, Iron, Zinc, and Chloride
The essential nutrients- plants take up only
INORGANIC nutrients
Carbon (C), Hydrogen (H), Oxygen (O) - Constituent of all organic molecules
Nitrogen (N) - Component of proteins,enzymes, and nucleic acids
Phosphorus (P) - In nucleic acids, phytin, coenzymes, adenylases; regulatory function
Potassium (K) - Osmoregulation; enzyme activator, and protein component
Calcium (Ca) - In pectates, and regulatory protein ; regulation of enzyme
Magnesium (Mg) - Integral component of chlorophyll, Mg-ATP; activator of phosphorylation, RuBP carboxylase
Sulfur (S) - Constituent of several coenzymes, vitamins and amino acids
Iron (Fe) - Components of Fe- and Fe-S proteins, cytochromes, and ferredoxins
Copper (Cu) - Activator of several oxidases and lignin synthesis
Zinc (Zn) - Activator of enzymes
Manganese (Mn) - Enzyme activator and photosynthetic evolution of oxygen (Hill reaction)
Molybdenum (Mo) - Enzyme component essential for nitrogenase in bacteria for N2-fixation
Boron (B) - Complex with protein
Beneficial Elements
o Elements which promote plant growth in many plant species but are not absolutely necessary for completion of the plant life cycle
o Silicon, sodium, cobalt, and selenium
Decline in Soil Fertility
▪ Soil erosion
▪ physical loss and displacement of the fertile topsoil
▪ Geological erosion
▪ Wind erosion
▪ Water-borne erosion
▪ Accelerated erosion due to human activity
▪ Crop removal
▪ Conversion of nutrients to unavailable forms
▪ Formation of insoluble forms
▪ Microbial mediated transformations
▪ Volatilization (especially nitrogen)
▪ Leaching
✔pH affects the growth of plant roots and soil
microbes
✔Root growth favors a pH of 5.5 to 6.5 (6-7)
NUTRIENT DEFICIENCIES
* Mineral nutrient deficiencies occur when the concentration of a nutrient decreases below its typical range
* Deficiencies of specific nutrients lead to specific visual, often characteristic, symptoms reflective of the role of that nutrient in plant metabolism
NUTRIENT DEFICIENCY SYMPTOMS
❑ Chlorosis
- (uniform or interveinal) or yellowing of the leaves due to chlorophyll degradation
❑ Necrosis
- (tip, marginal, or interveinal) or death of leaf tissue
❑ Lack of new growth
- which may result in death of terminal or
axillary buds and leaves, dieback, or resetting
❑ Accumulation of anthocyanin
- resulting in reddish coloration of leaf tissues
❑ Stunted leaf growth
- with green, off-green, or yellow color
Patterns of deficiency
▪ Patterns of deficiency are important in identifying which nutrient is deficient or lacking
▪ The location where a deficiency reflects the mobility of a nutrient
▪ Nutrients are redistributed via movement through the phloem
▪ If the deficiency is seen in old leaves = nutrient is mobile
▪ If the deficiency is seen in young leaves =nutrient is fixed or immobile
How to address nutrient deficiency?
1. Establish an attainable yield level – the crop’s total needs
2. Calculate the nutrient requirement of the crop
3. Effectively use existing nutrients
a. organic fertilizers
i. manure
ii. plant biomass
iii. vermicompost
iv. fermented plant juice
b. nutrients from irrigation water
c. indigenous soil nutrients
4. For deficiencies, top up with or add inorganic fertilizers
Development
- The attainment of size by virtue of growth and architectural style by morphogenesis (differentiation of cells into tissues, organs and organisms)
Aspects
1. Growth
2. Differentiation
3. Organization
Growth
- the irreversible increase of cell number, and essentially its dry mass or weight
- increase in size does not mean an increase in growth.
Growth curve
* Cells/organs show a definite pattern of growth
- stages of in growth curve
- lag, logarithmic, stationary
Differentiation
* Reflects the orderly processes by which genetically identical cells become different, forming specialized tissues and
organs
* The reflection of change in the cell’s biochemical program, controlled by developmental genes
Dedifferentiation
-the reversal of the cell specialization
- Important in the repair of injury, where cell near damaged sites become totipotent and reprogram their development
Organization
– orientation and integration of differentiated cells in space together with regulated growth 🡪 whole plant
Morphogenesis
* the orientation and integration of differentiated cells in space together with regulated growth, and the consequent attainment of form and structure of the complete organism.
development aspects (complete)
- growth
- differentiation
- pattern formation
- morphogenesis
- Plants, develop according to a predetermined genetic blueprint
- Expression is greatly influenced by signals received from the external environment
- Plants are always undergoing development.
Localization of Growth
- Essential characteristics of organisms
- take up relatively simple substances from environment and synthesize these to complex substances
- At cellular level
- increase in living material leads to increase in cell size and
ultimately cell division 🡪 complex process in multicellular
- increase in living material leads to increase in cell size and
Localization of Growth
* Growth is restricted to certain embryonic regions called the meristems
Meristems
- Where plant growth occurs
- Site of repeated cell division of unspecialised cells
- Cells differentiate, and become specialised in relation to the function they will perform
- actively dividing cells
Basic Structures involved in Plant Growth
and Development
Embryo
- Cotyledons, shoots and root apical meristems
Meristems
- Shoot
- Axillary root (apical and lateral)
- Floral
- Cambiums (cork, vascular
Types of Meristems
Apical
- tips of roots and shoot
- site of primary growth in a plant
Lateral
- side portions, arising from the cambium (base of nodes and stems),
- responsible for secondary thickening of the stem and roots
Intercalary
- inserted between regions of differentiated tissues
Types of Growth
1. Indeterminate
(ricebean, winged bean)- apical meristems of the roots and stems remain permanently
embryonic over long periods
2. Determinate
(corn, rice, mungbean)- other plant parts (leaves, flowers, fruits) are embryonic for limited period before the plant reaches maturity, have precise morphology and
definite number of parts
Internal Growth Mechanisms
Correlation Effect
- The regulatory effects exerted by one part of the plant on the growth or development in another part
Organ Differentiation
- As shoot increases in bulk, the size of the root system becomes proportionately larger
- Reduction in vegetative growth when the plant is fruiting
- Stimulation of fruit growth by hormones produced in the developing seeds
- Stimulating effects of buds/leaves on the rooting of stem cuttings
The Biological Clock
* Many aspects of plant behavior exhibit periodic oscillations that appear to be controlled by an internal time measuring system: the endogenous biological clock
Manifestations
- Diurnal rise and fall of leaves (sleep movements)
- Photosynthesis is diurnal
Criteria to distinguish simple periodic phenomena and rhythm driven by an endogenous clock
1.Persists in the absence of external clues
2.Can be reset by external signals such as light and temperature
3.No lasting effect of temperature on the timing of the clock-driven rhythm
Classification of Biological Rhythms
1. Circadian Rhythm (circa=about+diem=day) = 24 hours eg bean movement (hyponasty, epinasty) (example: Portulaca, Calathea, rain tree or Fertility Tree of UPLB)
- Lunar rhythm
= 28 days, between one full moon to the next - Annual rhythm – (flowering of fire trees, cherry blossoms and kapok every summer)
- Ultradian rhythm
= <24 hrs
Plant Movements
Categories
* Growth movements
* result of differential growth within an organ or between 2 different organs (irreversible)
- Turgor movements
- Results from volume changes in certain cells due to changes in osmotic potential (water) pressure due to the influx or efflux of ions which in turn cause water to move in and out of the cells (reversible, but not all the time)
plant responses to stimuli
- it is the growth towards or away from an environmental stimulus
- movement not oriented toward or away from an environmental stimulus
- give the tropism and nastic movement for the following stimulus: light/dark, gravity, touch, temperature, chemical, water
- tropism
- nastic movement
- light/dark = phototropism; photonasty
- gravity = gravitropism; none
- touch = thigmotropism; thigmonasty
- temperature = thermotropism; thermonasty
- chemical = chemotropism; chemonasty
- water = hydrotropism; hydronasty
Tropisms
* Result from differential growth of specific organs of a plant
- Positive tropisms
- the plant moves toward the stimulus- –
- ex. bending toward light
- Negative tropisms
- movements away from the stimulus
movement in response to light
Phototropism
Gravitropism
Growth movements in response to gravity
❑ Shoots
* negatively gravitropic, away from the center (-)
* plant shoots exhibit negative gravitropism because they grow away from gravity
❑ Roots
* positively gravitropic, towards the earth’s center(+)
❑ directional response of a plant organ to touch or physical contact with a solid object
❑ curling of threadlike appendages in vines
Thigmotropism
- changing position and facing normal to the sun throughout the day
- the solar tracking of plant organs- example: sunflowers
Heliotropism
Photoperiodism
Long-day plants
- Flower when daylength is longer than a critical value
Short-day plants
- Flower when the daylength is shorter than a critical value
Day-neutral plants
- Flower when they become mature regardless of daylength
Long day – malunggay, aster, gladiola, fire tree, golden shower
Short-day – beans, poinsettia
Flowering
* Mode of Reproduction (self, cross, asexual)
* Mode of Pollination – insect, wind, water, birds
* Fertilization
* Fruit/seed setting
* Harvesting
* Postharvest Handling
* Types of seeds based on storage behavior
- Dormancy - a slowdown in an organisms metabolic rate
- Seed dormancy – inability of viable seeds to germinate given favorable conditions for germination.
- Normally, a flower which is pollinated develops into a fruit, containing seeds derived from the fertilized egg cell
- Parthenocarpy - fruit development without fertilization
- the collective term for aging processes that lead to the death of a plant or plant part
- Leaf colors are an example that results from changes in light quality and photoperiod that trigger chlorophyll destruction, unmasking the other pigments in the leaf
SENESCENCE
Hormones and Growth Regulation
Phytohormones
* Organic substances other than nutrients
* Effective at low concentrations
* Naturally-occuring
* Modify plant growth and development
(quantitative/qualitative)
More than one hormone is involved in the control of physiological processes but only one tends to dominate the control process
- Hormones
– organic substances effective at low concentrations that modify plant growth and development
– produced naturally by plants - Plant Growth Regulators
– may be synthetic compounds (e.g., IBA and Cycocel) that mimic naturally occurring plant hormones, or
– may be natural hormones that were extracted from plant tissue (e.g., IAA)
- synthesized in shoot apical meristems, young leaves, seeds and fruits
- promote growth in molar concentrations of 10-3 to 10-8
Indoleacetic Acid (IAA)
- Auxin produced chemically
- synthesized from indole or tryptophan
- Auxin produced in apical buds - inhibit the activation of buds lower on the stems (apical dominance)
- Promote lateral and adventitious root development
- Fruit development requires auxin produced by the developing seed.
- Auxin pastes applied to developing ovaries can promote parthenocarpy (fruit development in the absence of fertilization)
- toxic in large concentrations
- affect mostly dicots but not monocots
- Monocots seem to be able to rapidly degrade the synthetic auxins
- Synthetic auxin herbicides include 2-4-D and 2-4-5-T (Agent orange of the Vietnam era contains synthetic auxin)
- Used as defoliants
- Used as weed killers
Auxins
- phenyl urea derivatives of adenine, one of the molecules in DNA
♣ found in actively dividing tissues of seeds, fruits, leaves and root tips, and wound tissue sites
♣ transported through xylem to the rest of the plant
♣ promote cytokinesis
♣ work in conjunction with auxins, which promote elongation and cell expansion
♣ promote axillary/lateral bud growth by over-riding the apparent inhibiting effect of auxin
Cytokinin
controls what tissues differentiate in the tissue culture
Ratio of Cytokinins to Auxin
Discovery of Gibberellic Acid
- Many seeds contain a variety of different gibberellins - Over 100 different gibberellins (organic acids synthesized from mevalonic acid)
- Gibberellins are produced in roots and younger leaves, with seeds having the highest concentration
- Most effects of gibberellins are shown only in concert with auxins
Effects of Gibberellins on Elongation
- Reversal of genetic dwarfism GA
- Bolting of biennials, to produce flowers during the first growing season
- Gibberellins like auxins, promote parthenocarpy
- commercial applications in grape industry, where grapes grow larger, and with longer internodes
- inhibits growth activities in times of environmental stress rather than by promoting growth
- often serves as an antagonist to the other growth promoting hormones in plants.
- ABA promotes seed dormancy
- Low levels of ABA in maturing seeds promote premature germination
- ABA is also referred to as the stress activity hormone
- ABA promotes stomata closure during leaf water deficit conditions by activating K+ ion transport out guard cells
Abscisic Acid
- synthesized from the amino acid methionine
- sole plant growth regulator known that is a gas
- Promotes flowering
- promotes leaf senescense
Ethylene
CROP GROWTH STAGES (rice)
vegetative phase
- short duration: 35-55 days
- medium duration: 55-75 days
- long duration: 75-95 days
reproductive phase
- 35 days
ripening phase
- 30 days
vegetative stages (corn)
ve (emergence)
v1 (one leaf with collar visible)
v2 (two leaves with collars visible)
v(n) ((n) leaves with collars visible)
vt (last branch of tassel is completely visible)
- corn vegetative stages
reproductive stages (corn)
r1 - silking
r2 - blister
r3 - milk
r4 - dough
r5 - dent
r6 - physiological maturity - the black abscission layer has formed
- corn reproductive stages
