Lecture 12 Flashcards
What is the importance of light?
Plants use it to measure time of day/year so they can adjust their growth and acclimate to the environment
Define light quantity/light intensity
The number of photons incident upon a surface
Define light quality. What is its importance?
The integrated colour composition of photons incident upon a leaf
It is used to tell a plant where it resides within a canopy
What light quality does the shade have? The open air?
Green
Dynamic due to sunflecks
Blue
How does day light vary depending on latitude?
The closer to the equator (in the tropics) the less variation bw seasons (sun all around)
How does daylight work as a developmental que? What types of plants does it give rise to? (2) At what levels can Pr/Pfr be found and what do they promote?
Short day plants: short days or long periods of darkness initiate developmental events (triggered when daylight is shorter than its threshold)
- flowering time: late summer to autumn
- Pfr degrades to Pr (weak Pfr signal to wreak to suppress flowering = plant flowers)
Long day plants: long days beyond their trigger threshold signal developmental events
- flowering time: late spring to early summer
- high Pfr pool (strong to promote flowering)
Define photosynthetic pigments (2)
Carotenoids and chlorophylls
Name the 3 types of light receptors and their associated colour
Cryptochromes (blue), Phototropins (blue), Phytochromes (red/green)
What are the two types of phytochrome and which is inactive? What light must it be exposed to for conversion?
Pr and Pfr
Pr is synthesized in the dark and inactive
Pr -> Pfr: orange/red
Pfr -> Pr: far-red
What is the function of the phytochrome? (5)
Regulate seed germination Promote de-etiolation Trigger greening in seedlings Inhibit internode elongation Regulate photoperiodic responses
What are photoperiod responses? (3)
Inhibit flowering in short day plants
Promote flowering in long day plants
Que bud break (spring) and dormancy (fall)
Germination controls of a dormant seed/bud:
Dormant seed: temperature & moisture cue -> potentiated seed -> daylight cue -> germination
Dormant bud: daylight cue -> potentiated bud -> temperature & moisture cue -> bud break
During the winter/spring, which phytochrome pool is bigger? Which light is abundant?
WINTER: large Pr (inactive) pool
- less red light present = longer nights
- have more time to revert back from Pfr
SPRING: large Pfr (active) pool
- more red light present = shorter nights
- have less time to revert back from Pfr
Environmental conditions that regulate germination (3)
Daylight (decide if season is OK for germination)
Light quantity (decide whether are too deep in the soil)
Light quality (deduce where plant is (under canopy or open field))
What is etiolation? What does it cause?
Etiolation is the process of a plant growing in a lack of light causing a weak, long stem, large distance bw internodes, pale colour, smaller leaves
When a seed emerges from the soil what must it do?
Explain what these programs are (2)
Switch it’s programming from pre-emergence to post-emergence
Describe pre-emergence (what occurs, phytochrome role)
Suppresses leaf emergence/expansion, suppresses synthesis of chlorophyll/photosynthesis proteins, maintain hypocotyl hook, maximize stem elongate rate
Phytochrome role: large Pr pool, absent ref light, negligible Pfr
Describe post-emergence (what occurs, phytochrome role)
Promotes leaf emergence/expansion, promote synthesis of chlorophyll/photosynthetic proteins, straighten the hypocotyl hook, slow stem elongation rate
Phytochrome role: small Pr pool, abundant orange/red light, scarce far-red light, large Pfr pool
What is florigen? Where does it originate from?
A trans located chemical that induces flowering in a plant
Origin: companion cells
First step for flower induction is florigen production: explain the pathway.
Phytochrome (Pfr) -> circadian clock -> constans transcription factor -> activated Flowering Locus T (FT) gene -> florigen protein produced in companion cells of leaves -> move into phloem then to SAM
Second step for flower induction is triggering the gene for bud formation: explain the pathway.
Florigen (Hd3a) from the leaf enters the shoot apical meristem cell -> binds to florigen receptor (14-3-3) in the cytoplasm -> enters the nucleus -> binds to DNA binding protein (OsFD1) to make a florigen activation complex -> transcription activated to make gene that triggers bud formation
What arises from growing in the Sun Program and the Shade Program? (4/4) What mediates sun vs shade development?
THE SUN PROGRAM
Thick mesophyll with many chlorenchyma layers
Abundance of Rubsico and photosynthetic enzymes
Slower stem/petiole elongation
High investment in vascular tissue
THE SHADE PROGRAM Thin mesophyll with few chlrorenchyma layers Low investment in photosynthetic enzymes More rapid stem, petiole elongation Reduced vascular tissue investment
Phytochromes mediate the development
The five forms of Phytochromes in eudicots
PhyA (regulates germination/de-etiolation, abundant in dark/down regulated in light)
PhyB (always present, regulated flowering response/photoreversible seed germinations, used in shade detection/avoidance)
PhyC (regulates hypocotyl elongation in light, shade avoiding)
PhyD (regulated petiole/internode elongation, shade avoiding, flowering time)
PhyE (regulates seed germination, flowering time, petiole elongation)
Monocots only have A-C
What are cryptochromes? Their function? (5)
A group of flavoprotein blue light receptors that regulate plant and animal responses to light intensity
Functions: contribute to phototropism, resets Circadian clock, stimulate stomatal opening, contribute to de-etiolation/greening responses/promote cotyledon expansion, activated high-light developmental program
What are anthocyanins?
Water soluble vacuolar pigments that are red/purple/blue that protect against UV radiation in plant tissues
Methods of enhancing nutrient acquisition (6)
Develop more absorptive surface area (more roots (clusters, hairs etc), form mycorrhizae)
Enhance uptake per unit root surface area
Produce chelators to mobilize nutrients
Generate more prolific rhizosphere with greater bacterial action/more chemical degradation
Evolve a symbiosis with nitrogen fixing bacteria
Evolve ability to trap and digest insects
The Nitrogen Cycle important processes (7)
Nitrogen Fixation (atmospheric N2 to biologically useful forms)
Assimilation (uptake of N-species by plants)
Nitrate Reduction (reduction of nitrate to ammonium by plants)
Nitrification (oxidation of ammonium in soil by nitrifying bacteria)
Consumption (by animals/fungi/bacteria)
Decomposition (by bacteria/fungi)
Ammonification (release of ammonium from proteins/amino acids)
Denitrification (oxidation of N2 has by anaerobic bacteria)
Nitrogen Assimilation (what is it, what enzymes does it use, how much energy does it take up?)
Uptake of N-species into plants (humans can’t do this)
Enzymes: glutamine synthetase (produces glutamine), glutamate synthase (produces glutamate)
1ATP, 1NADH per NH4+
Nitrogen Reduction (what is it, what enzymes does it use, how much energy does it take up?)
Reduction of nitrate to ammonium by plants
Enzymes: nitrate reductase (forms nitrite then ammonium)
8NADH (v expensive)
Nitrification (what is it, what are the dates of nitrates/ammonium?)
Two step process of oxidizing NH4+ by bacteria
Nitrates = don’t bind to colloids bc they’re both negative so they are readily leached from soil into ground water
Ammonium = cations readily bind to colloids and are immobilized in the cell
Denitrification (what is it?)
Return of sequestered soil nitrogen to the atmosphere in the absence of O2 by pseudomonas
Nitrogen Fixation (what is it, what Enzyme does it use, how much energy does it take, what two types of Fixation does it have?)
Conversion of atmospheric nitrogen to biologically useful forms
Enzyme: nitrogenasen
4NADPH
2 types: symbiotic fixation (bacteria living with high plant), free-living Fixation (prokaryotes fix N in their own rhzisophere)
Methods of protecting nitrogenase from O2
Nodulated plants (thick walls) Legumes (leghemiglobin) Cyanobacteria algae (heterocyst)
Fertilization methods (5)
Traditional: infield/outfield, shifting cultivation, floodplain irrigation, rotational agriculture
Modern: addition of N:P:K
