Plant development and environmental perception Flashcards
plant development cellular aspects of development how cells respond to stimuli
what are angiosperms
plants that have flowers and produce seeds enclosed within a carpel
what are the two main groups of angiosperms
eudicots and monocots
what is a cell
the fundamental unit of life
what is a tissue
a group of cells consisting of one or more cell types that together perform a specialized function
what is an organ
it consists of several types of tissues that together carry out particular functions
what do plants absorb below the ground
water and minerals
what do plants absorb above the ground
light and carbon dioxide
what are the 3 basic organs of a plant
stems, leaves and roots
what does the root system consist of
the roots
what does the shoot system consist of
stems and leaves
what is a root
an organ that anchors a vascular plant in the soil, absorbs minerals and water and often stores carbohydrates and other reserves
what is the first organ to emerge from a germinating seed
the primary root
what does the primary root branch into
lateral roots
what is a taproot
the main vertical root that develops from the primary root and is exhibited in tall erect plants - facilitates anchorage
what is a fibrous root system
a thick mat of slender roots spreading out below the soil surface
what is an adventitious root
a root that grows in an unusual location e.g. roots arising from stems or leaves
what are root hairs
thin finger like extensions of root epidermal cells
what are mycorrhizal associations
root symbiotic interactions with soil and fungi that increase a plants ability to absorb minerals
what is a stem
a plant organ bearing leaves and buds
its chief function is to elongate and orient the shoot in a way that maximises photosynthesis by the leaves
they also elevate reproductive structures, facilitating the dispersal of pollen and fruit
can a green stem perform photosynthesis
yes but it is limited
stems consist of nodes, what are these
the points at which leaves are attached
stems consist of internodes, what are these
the stem segments between nodes (between the points where leaves are attached
what is the main photosynthetic organ
the leaves
how do monocots and eudicots differ
by the arrangement of veins ((the vascular tissue) in the leaves
- most monocots have parallel veins
- most eudicots have a branched network of veins arising from a major vein
what are the 3 fundamental tissue types of vascular plants
dermal, vascular and ground tissues
what is the function of the dermal tissue system
serves as an outer protective covering of the plant
what are the functions of trichomes
reduce water loss
reflect excess light
defend against insects
what is the function of the vascular tissue system
facilitates the transport of materials through the plant and provide mechanical support
what are the 2 types of vascular tissue
xylem and phloem
what is the function of xylem
conduct water and dissolved minerals upward from roots into the shoots
what is the function of phloem
transports sugars from where they are made to where they are needed or stored
what is ground tissue
tissue that is not vascular or dermal - it includes specialised cells for functions such as storage, photosynthesis, support and short distance transport
what is intermediate growth
the process of plants growing throughout their life
why can plants continually grow
because they have undifferentiated tissues called meristems, containing cells that can divide, leading to new cells that elongate and become differentiated
which type of plant does not grow continuously
dormant plants
describe the growth of most animals
determinate growth - they stop growing after they reach a certain size
what are the 2 main types of meristems and what type of growth do they enable
apical meristem - primary - length
lateral meristems - secondary - thickness
roots and stems grow intermediately/determinately
intermediately
leaves grow intermediately/determinately
determinately - because the oldest leaves at the bottom of the plant would be large and heavily shaded, unable to photosynthesise maximally
what is the function of stomata
they are pores interrupting the leaf epidermis which allow exchange of carbon dioxide and oxygen between the surrounding air and the photosynthetic cells in side the leaf
they are also major avenues for the evaporative loss of water
what does the stomatal complex consist of
a stomatal pore flanked by 2 specialised epidermal cells known as guard cells which regulate the opening and closing of the pore
what is a parenchyma cell
a relatively unspecialised plant cell type that carries out most of the metabolism, synthesis and stores most of the organic products and develops into a more differentiated cell type
what type of cell does mesophyll mainly consist of
parenchyma
what is a bundle sheath
a layer of cells that encloses the veins and regulates the movement of substances between the vascular tissue and the mesophyll
(prominent in leaves that carry out C4 synthesis)
contrast primary growth in roots and shoots
roots - primary growth occurs in 3 successive stages, moving away from the tip of the root: the zones of cell division, elongation and differentiation
shoots - occurs at the tip of apical buds, with leaf primordia arising along the sides of an apical meristem - most growth in length occurs in older internodes below the shoot tip
what are leaf primordia
finger like projections along a shoot apical meristems from which a leaf arises
what is a lenticel
a small raised area in the bark of stems and roots that enabled gas exchange between living cells and the outside air
why do stomata need to be able to close but lenticel s do not
stomata need to close because water evaporation is much more intensive in leaves than from the trunks of woody trees as a result of higher SA to volume ratio in leaves
what is meant by plant growth being modular
it follows patterns that are repeated over and over again
what does morphogenesis (plant form) arise from and what is it dependent on
arises within cell walls and depends entirely on cell division and cell lineage
the first 4 divisions of embryogenesis give cell ……….
bulk
the fifth division (to 16 cell stage) results in what
cell layers
tripoblasts/atripoblasts form root hairs
triipoblasts
tripoblasts/atripoblasts do not form root hairs
atripoblasts
what happens to the fassiculated mutant of Arabidopsis
it has a loss of positional interactions - the cell walls become disorganised
what happens to the knolle mutant of Arabidopsis
it has a loss of cell division control - knolle is a structural protein needed to form the cell division plate - the mutant has irregular and incomplete cell divisions
simple rules of association provide guidelines for what
development
what is pattern formation
the development of specific structures in specific locations
where do plant developmental stages (phases) occur
the apical shoot meristem
what are phase changes
in plants it is a morphological change that arises from a transition in shoot apical meristem activity
what does GLABRA-2 do
if it is expressed the cell is hairless but if it isn’t expressed then the cell will develop a root hair
do nodes and internodes maintain juvenile status even after the shoot apical meristem has changed to adult phase
yes - new leaves that develop at juvenile nodes will also be juvenile even though the apical meristem is producing mature nodes
describe 3 difference between animal and plant development
plants:
- intermediate growth
- juvenile and mature phases are found on the same plant
- cell differentiation is more dependent on final position
animals:
- determinate growth
- juvenile and mature phases not found on the same individual
- cell differentiation is more dependent on cell lineage
what phase change does flower formation involve
a change from vegetative growth to reproductive growth
is floral growth usually indeterminate or determinate
determinate
how does the production of a flower by a shoot apical meristem affect growth
it usually stops the primary growth of that shoot
which genes control the switch from vegetative growth to flowering
meristem identity genes
how do meristem identity genes affect flowering
their protein product acts as a transcription factor that regulates the genes required for the conversion of intermediate vegetative meristems to determinate floral meristems
what are the 4 floral organs
sepal, petal, stamen or carpel
what do organ identity genes belonging to the MADS-box family encode
transcription factors that regulate development of the characteristic floral pattern
what can a mutation in organ identity genes in plants cause
abnormal floral development such as petals growing in place of stamens
what process leads to polarisation
germination
what factors induce germination
- light (rhizoid grows on shaded side)
- heat (rhizoid grows on warm side)
- osmotic gradient (rhizoid grows towards water)
- pH (rhizoid grows towards alkaline pH)
- salt rhizoid grows towards salt)
- fertilization (rhizoid at entry point)
describe the steps in polarisation due to fertilisation
- in fertilisation, a calcium wave triggers secretion of cell wall material
- calcium current is initiated and enters at future rhizoid end
- actin is organised, and secretion is directed to future rhizoid
- polarity is fixed and the rhizoid tip is visible
- mitosis and cell division occur
what are rhizoids
long tubular single cells
what is the regulatory factor of polarity
calcium
root structure arises from ……….. divisions that initiate cell lineage
meristems
how is polarity controlled between cells in plants
Apical-basal polarity is maintained by hormonal gradients, especially auxin
Plant tissue structure arises from cell lineages with defined cell fates originating from established ……………
cell polarity
what do pin proteins do
transport auxins out of cells (efflux carriers)
what happens to the pin-1 mutant
disturbs shoot form and root growth direction
what happens to the pin-2 mutant
mutant seedlings show loss of gravitropism (movement or growth in relation to gravity) in the root - they can’t access nutrients and water from the soil as well
in signal transduction what is a receptor need for
to sense the stimulus - the receptor converts the signal into a biological meaningful form
what are second messengers
- they amplify the internal biochemical signal from the receptor
- they transfer the signal to the response mechanism
by opening and closing of stomata, what is balanced
the need for CO2 for photosynthesis against the prevention of water loss
abscisic acid is involved in which kind of tress
drought - drought stimulates roots to synthesise abscisic acid which then travels to the leaves with the transpiration stream
is abscisic acid a stimulus for stomatal closure or opening
closure
the abscisic acid stimulus overrides the need for ……….
CO2
what are the 3 main ion channels used by guard cells
Ca
Cl
K
how can we measure ion channels
using a method called clamping
we can also measure how single proteins function using a method called patch lamp
ion channels are pores with …………. gates
regulated
how does gating of ion channels arise
from changes in protein conformation in the channel
how does abscisic acid trigger closing of stomata
it triggers potassium and chlorine efflux and suppresses influx which triggers closing of the stomata
the abscisic acid affects the gating of the channels affecting their frequency of opening
what are jaffes laws
the laws for determining if something is a secondary messenger
- the stimulus, second messenger and response must be related in time and space
- blocking a signal or messenger must block the signal and response downstream
- introducing a second messenger without a primary stimulus must give the response downstream
abscisic acid triggers a rise/decrease in Ca in the cytosol
rise
Ca is needed to regulate what
ion channels
Ca in the cytosol promotes/suppresses abscisic acid action on K and Cl channels
suppresses
is Ca sufficient to regulate ion channels without abscisic acid
yes
give examples of stimuli that trigger signal transduction pathways
light
hormones
physical environment
pathogens
signal transduction pathways link signal ………. to ………….
reception to response
what is etiolation
morphological adaptations for growing in darkness
describe a dark grown potato
tall stems and unexpanded leaves - an adaptation enabling shoots to penetrate the soil
the roots are short as there is little need for water absorption due to the lack of water loss due to the lack of leaves
describe a potato grown in light
short sturdy stems
broad green leaves - to enhance photosynthesis
long roots - to enhance water absorption
what is de-etiolation
the changes a plant undergoes due to being exposed to light
the light signal is transduced to de-etiolation response
what are the 3 main steps of a signal transduction pathway
reception
transduction
response
what are signals detected by
receptors
what is the receptor involved in de-etiolation
phytochrome
where is the phytochrome located
cytoplasm
where are the majority of photoreceptors found
the plasma membrane
what causes golden rice
it is an aurea mutant which has less phytochrome (this reduces the level of chlorophyll because phytochromes detect red light that chlorophyll absorbs)
in the absence of chlorophyll the yellow and orange accessory pigments become more prominent
cytosolic changes in calcium concentration play an important role in ………… signal transduction
phytochrome
how do phytochromes affect calcium concentration
- phytochrome activation leads to the opening of calcium channels increasing cytosolic levels of calcium
describe the role of phytochrome in de-etiolation
- light signal is detected by the phytochrome receptor, activating 2 signal transduction pathways
- a. one pathway uses cGMP as a second messenger that activates kinase
b. the other pathway increases the cytosolic level of calcium which activates another kinase - both pathways lead to the expression of genes (by transcription factors activated by kinase) for proteins that function in the de-etiolation response
what are the 2 main mechanisms by which a signalling pathway can enhance an enzymatic step in a biochemical pathway
transcriptional regulation
post translational modification
what is transcriptional regulation
controlling the level of mRNA encoding a specific enzyme
what do post translational modifications do
activate pre-existing enzymes
give examples of post translational modifications
phosphorylation
what enzymes are important in stopping signal transduction pathways after the stimulus has faded
phosphatases - they dephosphorylate
what are the 2 types of transcription factors
activators (increase transcription) and suppressors (decrease transcription)
why is etiolation advantageous
etiolated growth is beneficial to seeds growing underground or under dark conditions.
by devoting more energy to stem elongation and less to leaf expansion and root growth, the plant increases the likelihood that the shoot will reach the sunlight before its stored food runs out
which hormones enhance stem elongation
auxin and brassinosteroids
what is a hormone
signalling molecule that is produced in low concentrations by one part of an organism and is transported to other parts triggering responses in target cells and tissues
what are plant growth regulators
plant hormones
where is auxin found
shoot apical meristems and young leaves
what is the function of auxin
simulates stem elongation
promotes formation of lateral and adventitious roots
regulates development of fruit
functions in phototropism and gravitropism
where are cytokinins found
mostly synthesised in the roots - and are transported in the xylem sap
what is the function of cytokinins
regulation of cell division in roots and shoots
promote movement of nutrients
stimulates seed germination
where is ABA found
almost all plant cells have the ability to produce ABA
what is the function of ABA
inhibits growth
promotes stomatal closure during drought stress
promotes seed dormancy and inhibits early germination
what is a tropism
any growth response that results in plant organs curving towards or away from light
what is phototropism
the growth of a shoot towards or away from light
why do high concentrations of auxin inhibit growth
high auxin concentrations may induce production of ethylene which hinders growth
explain how proton pumps play a major role in the growth response of cells to auxin
- in a shoots region of elongation, auxin stimulates the plasma membranes proton pumps pumping H from the cytoplasm
- H increases the voltage across the membrane and lowers the pH in the cell wall
- acidification of the cell wall activates proteins that break H bonds between cell wall constituents, making the cell wall more flexible
- increasing the membrane potential enhances ion uptake into the cell which causes osmotic uptake of water and increased turgor
- increased turgor and increased cell wall plasticity enable the cell to elongate
what is IBA used for
it is used in the vegetative propagation of plants by cuttings
treating a detached leaf or stem with IBA often causes adventitious roots to form near the cut surface
why are synthetic auxins used as herbicides
they can be quickly broken down by monocots but overdose eudicots, eliminating eudicot weeds
what is apical dominance
the ability of the apical bud to suppress development of auxiliary buds (controlled by various hormones including auxin and cytokinins)
how do cytokinins slow aging
they inhibit protein breakdown and stimulate RNA and protein synthesis
what is the role of gibberellins
stimulate stem elongation, pollen development, fruit growth, germination
what is the function of ethylene
promotes fruit ripening, leaf abscission, promotes root hair formation
induces triple response in seedlings
what is the function of brassinosteroids
promotes root growth at low concentrations but inhibits it at high concentrations
what is the ABA response to drought
- ABA accumulates in the leaves
- by affecting the second messenger, Ca, ABA cause potassium channels in the plasma membrane of guard cells to open leading to a massive loss of potassium ions from cells
- the accompanying osmotic loss of water reduces guard cell turgor and leads to the closing of the stomatal pores
- as a result less transpiration occurs
many plants prone to wilting are deficient in what
ABA - it acts as a drought signal
what is the triple response induced by ethylene
it enables seedling shoots too avid obstacles
the 3 parts of the response are:
- slowing of stem elongation
- thickening of stem
- stem curvature that causes it to start growing horizontally
the stem resumes regular growth after the ethylene pulse lessens
what is senescence
the programmed cell death of certain cells or organs or the entire plant - ethylene is almost always associated with apoptosis in senescence
what is abscission and what is it controlled by
the natural detachment of parts of a plant, typically dead leaves and ripe fruit
it is controlled by a change in the ratio of ethylene to auxin. an aging leaf produces less and less auxin rendering the abscission layer more sensitive to ethylene. when ethylene targets the abscission layer, the cells produce enzymes which digest cell wall components
what forms after leaf abscission to protect the plant from pathogens
a protective layer forms on the remaining twig to prevent pathogen entry
what triggers the ripening of fruit
a burst of ethylene - the enzymatic breakdown of cell wall components softens the fruit and conversion of starches and acids to sugars makes the fruit sweeter
how do gibberellins promote stem elongation
they enhance cell elongation and cell division
- they activate enzymes that loosen cell walls allowing the entry of expansins - which along with auxin promote cell elongation
in many plants, ………….. and …………. must be present to allow fruit to develop
auxin and gibberellins
which hormone signals seeds to break dormancy and germinate
gibberellins
what are brassinosteroids similar to in animals
sex hormones and cholesterol
which hormone slows leaf abscission
brassinosteroids
what are tumour growths on leaves caused by
uncontrolled cell division and cell differentiation - can be caused by pathogens interfering with the function of auxin and cytokinin
what are ein mutants
ethylene insensitive mutants - they fail to undergo the triple response - they lack the ethylene receptor
what are eto mutants
ethylene overproducing mutants - they undergo the triple response
what are ctr mutants
constitutive triple response mutants - they don’t respond to inhibitors of ethylene synthesis so the ethylene signal transduction pathway is permanently turned on even id ethylene is absent
what is photomorphogenesis
the effects of light on plant morphology
what does an action spectrum show
the relative effectiveness of different wavelength of radiation in driving a particular process
what are the 2 major classes of light receptors
blue light photoreceptors - regulate phototropism, stomatal opening, slowing of hypocotyl elongation when a seedling breaks ground
phytochromes - regulate seed germination and shade avoidance
what is phototropism
growth of a plant shoot towards or away from light
which blue light photoreceptor is involved in mediating stomatal opening
phototropin (a protein kinase)
describe the role of phytochrome in the germination process
Pr in lettuce seeds exposed to red light is converted to Pfr stimulating germination.
when the red illuminated seeds are then exposed to far red light Pfr is converted back to Pr inhibiting germination
in nature the conversion to Pfr is faster than the conversion to Pr so germination is promoted
if a plant is exposed to multiple flashes of light, which flash will create the response
the last flash - the final light exposure is the determining factor
describe the role of phytochromes in shading avoidance
- if other trees in a forest shade a tree the phytochrome ratio will shift in favour of Pr because the - forest canopy screens out more red than far red light
- this is because pigments in the leaves of the canopy absorb red light and transmit far red light
- the shift in the ratio of red to far red light induces the tree allocates more of its resources to growing taller
- in contrast direct sunlight increases the proportion of Pfr which stimulates branching and inhibits vertical growth
what is a circadian rhythm
cycles with a frequency of 24 hours that are not directly controlled by an environmental variable
what is photoperiodism
a physiological response to specific night or day lengths e.g. flowering
what is a short day plant
they require a light period shorter than the critical length to flower (flower in winter instead of summer when light hours decrease)
what are long day plants
they require a light period longer than the critical length to flower (they flower in spring or early summer )when the photoperiod is long)
what are day neutral plants
they are unaffected by photoperiod and flower when they reach a certain stage of maturity
is flowering in short day and long day plants controlled by night length or day length
night length - so short day plants are actually long night plants and long day plants are actually short night plants
long day plants - maximum/minimum number of hours of darkness
maximum
short day plants - maximum/minimum number of hours of darkness
minimum
which colour of light is most effective in interrupting night length
red
where on the plant do flowers form
from apical or auxiliary bud meristems
which part of the plant detects changes in the photoperiod
leaves - they produce signalling molecules that cu bud to develop as flowers
how is flowering initiated
a gene called FT is activated in leaf cells in conditions favourable for flowering
the FT protein travels to the shoot apical meristem initiating the transition of a bud meristem from vegetative to flowering state
what is gravitropism
a plants response to gravity
roots display positive gravitropism (growing in direction of gravity) and shoots exhibit negative gravitropism (growing against gravity)
what is thigmomorphogenesis
changes in form that result from touch (mechanical perturbation)
what is thigmotropism
directional growth in response to touch
on a dry sunny day why does a plant wilt
it water loss by transpiration exceeds water absorption from the soil.
why may an overwatered house plant suffocate
the soil lack air spaces that provide oxygen for cellular respiration in the roots
- oxygen deprivation can induce ethylene production which causes some cells in the root cortex to die. this creates air space so oxygen can be taken up for respiration
how does salt affect plants
if plant soil is too salty this prevent water uptake into the plant
how do plants cope with cold stress
they alter their membrane lipid composition to keep it fluid - they increase the proportion of unsaturated fatty acid keeping the membrane fluid at low temperatures
how do plants cope with frost
when they freeze, water leaves the cytoplasm to go to the cell wall
the increase in the concentration of ions in the cytoplasm is harmful to the plant
plant have adapted by increasing cytoplasmic levels of specific solutes that are tolerated by the plant and help reduce the loss of water from the cell during extracellular freezing
unsaturation of membrane lipids is also increased helping to maintain fluidity
why are plant that are producing ABA warmer
because they cant undergo as much transpiration (evaporative cooling) due to stomatal closure
give an example of how plants can invade pathogens
by entering through openings in the epidermis e.g. the stomata
do plants have an adaptive immune system
no only an innate immune system
what are the 2 immune responses of plants to pathogens
- PAMP - pathogen associated molecular patterns
2. effector triggered immunity
what is the hypersensitive response
a plants localised specific defence response to a pathogen, involving the death of cells around the site of infection, preventing the spread of the infection
what is systematic acquired resistance
a defensive response in infected plants that helps protect healthy tissue from pathogenic invasion – a plant wide response (not localised)
what are the steps in defence responses of plants against pathogens
- pathogens infect leaf cells and secrete effectors, proteins that bypass PAMP immunity
- hypersensitive response occurs in response to effectors
- before infected cell die they release a signalling molecule (methysalicylic acid) to the rest of the plant
- the signalling molecule is converted to salicylic acid which induces systematic acquired resistance protecting the plant against many pathogens for several days
why is calcium effective as a second messenger in plants
because it is poorly mobile and largely bound in the cytosol
how many genes are involved in plant development
3
describe the mutant lacking the C gene in the ABC flower model
lacks stamen and carpel but has extra petals and sepals
describe the mutant lacking the B genes in the ABC flower model
lack stamen and petals but has extra sepals and carpels
describe the mutant lacking the A genes in the ABC flower model
lacks petals and sepals but has extra carpel and stamen
what is an apoprotein
photoreceptor protein
what is a chromophore
a small organic molecule that detects and absorbs light, attached to the apoprotein
