Plant And Algal Physiology Marc Knight

Front 1

Describe de-etiolation in arabidopsis

Back 1

It has two different developmental programmes, one in the light PHOTOMORPHOGENESIS
one in the dark SKOTOMORPHOGENESIS

the switch between the two is de-etiolation
When the seedling germinates its in complete drkness and is concerned with growing to leave the soil before seed reserves run out. When it senses light: inhibition of hypocotyl elongation and unfolding, expansion and greening of cotledons (the primary photosynthetic organs of seedlings).
The switchh is associates with expression of light regulated genes. Ie in the light rbcS, rbcL are both expressed (code for the small and large subunits of rubisco)
the etoplasts (chloroplasts which have not seen light) produce thylakoids and change to chloroplasts.

Front 2

Describe how light controls growth and development throughout the plant's life

Back 2

Can determine what time of year is it so the plant can alter its life-cycle to fit with conditions.
ie short day eg 8 hours, don't flower
long summers day produces flowers and seeds

Can tell the plant whether or not its surrounded by other plants eg tabocca plants grown with other plants will grow tall to forrage for light

Front 3

Name light receptors

Back 3

Red/far red: phytochromes : photomorphogenesis
Blue/UVA: crytochromes : photomorphogenesis
Green/Blue/UVA: phototropins : phototropic growth (directional)

Broad blue: Xanthophylls: stomatal movement

Front 4

Describe red:far red ratio information

Back 4

If red to far red ratio is high plant in open space ie feild if its low its in canopy and will therefore grow high and forage for light

Front 5

Describe how phytochrome acts as photoreceptors for red and far red light

Back 5

Phytochrome is a cyan-blue or cyan-green protein. It can exist as Pr and Pfr forms which can interconvert. In dark-grown etiolated seedlings phytochrome is present in its red light absorbing state Pr. Its converted to Prf quickly, darkness can slowly convert Prf back to Pr. However, outside of the laboratory plants are never exposed to pure red or pure far red light they're exposed to a mixture. Phytochrome detects the ratio (chlorphyll absorbs red but not far red light ) Plants growing beneath a canopy use phytochrome is senese to R:FR ratio to regulate shade avoidance, competitive interactions and seed germination.
Phytochrome is a dimer the two molecules bind in the COOH domain and is soluble

Front 6

Describe synthesis and activation of cytochrome

Back 6

in plastid heme converted to biliverdin converted to phytochromobilin which attatches to phytochrome at GAF domain to create holoprotein. Upon activation with red light D ring of phytochromobilin rotates exposing nuclear localisation sequence. Phytochrome moves into nucleus where it regulates gene expression. Some remains in cytoplasm where is mediates rapid biochemical changes.

Front 7

Descibe blue -light perception

Back 7

Cytochromes are blue-light receptors which medaite responses such as supression of hypocotyl elongation, promotion of cotyledon expansion, membrane depolarisation, anthocyanin production.

Cytochromes bind to flavin adenine dinucleotides (FAD). Blue-light absorption alters the redox status of the bound FAD chromophore triggering photoreceptor activation causing a conformational change in cytochrome enabling cytochrome to bind to other protein partners

Front 8

What the the cytochrome homologs?

Back 8

cry1 cry2 and cry3
cry 1 and cry2 have different effects (function of cry3 is not yet known)
cry2 is degraded under blue light, cry1 is much more stable. cry1 plays the major role in inhibiting stem elongation.
effects of cry1 aremore obvious under HIGH blue light, cry2 more obvious under low blue light.

Front 9

whats the evolutionary origin of cryptochromes?

Back 9

Have sequence similarity to bacteria photolyases (which catalyse blue-light dependent repair of UV damaged DNA)

Front 10

Explain shutting of stomata in response to light

Back 10

Stomal opening is regulated by blue light.
upon blue light irradiation the H+-ATpase shows a lower Km for ATP and a higher Vmax (via phosphorylation). It transports H+ across the membrane and increases the inside-negative electrical potentail driving K+ uptake. The accumulation of K+ facilitates uptake of water inot the guard cells leading to an increase in turgor pressure and stomatal opening.

Front 11

What are the two main causes of oxidative stress?

Back 11

1. Productive of reactive oxygen species from electron transport chain of photosynthesis
2. From oxidative agents in the environment eg ozone in atmosphere and heavy metals in the soil

Front 12

Oxidative stress caused by other stresses

Back 12

Virtually all stresses lead to oxidative stressesL
intense light, heavy metals, heat and cold, drought, pathogens. EXCESS LIGHT UNCOUPLES THE ELECTRON TRANSPORT CHAIN

Front 13

Describe ozone production

Back 13

Ozone occurs naturally at high altitude in the stratosphere. V high up high energy photons break oxygen into its monoatomic form which recombine at lower altitudes to form ozone Most ozone stays in stratosphere but some is in troposhere which comes into contacts with plants and animals but they've evolved to cope with low levels.
Combustion of carbon compounds leads to production of nitric oxides and peroxy radicals which combine with atmospheric oxygen to form ozone

Front 14

Describe plant responses to ozone

Back 14

Ozone enters through stomata (and then causes them to close)
creates oxyradicals and damages cells and lipids etc

Front 15

Name reactive oxygen species

Back 15

triplet oxygen, superoxide, hydrogen peroxide, hydroxyl radical, ozone

Front 16

What are the plant responses to oxidative stress?

Back 16

antioxidants reduce the levels of ROS once they are formed

catalyase catalyses hydrogen peroxide to water and oxygen.
A major hydrogen peroxide detoxifying system in plant cells is the ascorbate-glutathione cycle, in which, ascorbate peroxidase (APX) enzymes play a key role catalyzing the conversion of H2O2 into H2O, using ascorbate as a specific electron donor.

Front 17

What is drought stress?

Back 17

osmotic stress + oxidative stress. (similar to salt stress but without the ion toxicity stress).

Front 18

Which hormone does the plant produce in response to drought stress?

Back 18

ABA abscisic acid. Its important for gene expression and stomatal function. ABA causes stomata to close and as leaf water potential increases (becomes more negative) the concentration of ABA inccreases.
ABA is synthesized in the root in response to soil drying, is it transported in xylem is transpiration stream, it is synthesised and released from leaf mesophyll cells in response to water stress. ABA reaches the guard cells by symplastic and apoplastic routes.

Front 19

Describe distribution of ABA and pH

Back 19

The low pH in the apoplast favours protonation of ABA. ABA is transported in its protonated form, the anion form is 'trapped' and partitioned. ABA has a greater effect on acidic guard cells as more ABA is protonated.

Front 20

Describe control of gene expression in osmotically stressed/drought plants

Back 20

Osmotically stressed plants show an increase in Ca2+ levels which control gene expression

ABA regulates about 3000 genes via transcription factors MYB MYC and bZIP. One of the key roles of these drought genes is to produce compatable solutes such as amino acids and sugars which reduce water loss by osmosis and increase water uptake into cells.

Front 21

Whats the difference between chilling and freezing stress?

Back 21

Chilling is >0degrees and gives rise to oxidative stress
Freezing is <0degrees and gives rise to dessication-like stress

Front 22

Which plants are affected by chilling?

Back 22

Most tropical plants are damaged by temps 10-15degrees they're chilling sensitive

Front 23

What are the two types of chilling tolerant pants?

Back 23

Most temperate plants are chilling tolerant.
They can be subdivided into plants which can cold acclimate (ability to withstand freezing) and those which cannot.

Front 24

Whats the effect of chilling on membrane?

Back 24

Compresses saturated fatty acids making the membrane dense and less fluid. However, if unsaturates fatty acids are compressed the 'kinks' in their tails maintain fluidity in the membrane therefore more C=C bonds increases fluidity of the membrane these can be induced by desaturase enzymes and are important in chilling tolerance.
fab-1 mutants in Arabidopsiscan't desaturate membranes and loose chilling tolerance.

Front 25

Effect of chilling on the stomata

Back 25

Cause stomata to lock open if they were open when chilling began leading to water loss. This is an issue as the permeability of roots is low at chilling temperatures so lost water is hard to replace

Front 26

Effect of chilling on photosynthesis

Back 26

Affects both light and dark reactions. Major effect is on the electron transport chain leading to oxidative stress.

Plant produces anti-oxidants to 'treat symptoms' alters membrane fluidity to 'cure the disease'.

Front 27

Describe problems with freezing stress

Back 27

Result in intra and extracellular ice crystal formation. Intracellular ice physically shears the membrane and organelles.
However, the inside of the cell has high conc of solutes such as sugars and ions etc the cell wall has lower concs therefore water there freezes first. There is now zero water available in cell wall so water leaves cytosol by osmosis resulting in cellular dehyrdation and dessication stress.

Front 28

Describe chilling acclimation in the wild

Back 28

Temperate plants have the capacity for cold acclimation - a process whereby exposure to low but non lethal temerpatures (typically above zero) increases the capacity for low temperature survival. In nature its induces in Autumn.

Front 29

How is cold-acclimation shown in the lab?

Back 29

Take two wild-type Arabidopsis, keep both for 3 weeks at 20degrees but then chill one at 4degrees for 3 days before freezing both at -5degrees. the cold-acclimated plant will survive.

Front 30

Describe experiments with eskimo Arabidopsis mutants

Back 30

the eskimo mutant of Arabidopsis is constitutively freezing tolerant when frozen without acclimation the LT50 (temp that 50% die) is -11degrees. LT50 for WT was -6degrees.
Interestingly, once allowed to acclimate the LT50 for esk1 mutants is -15degrees sowing other genes and processes are involved.
Further analysis by Browse et al show high levels of proline (as seen is acclimated WT cells) in esk1 mutants before acclimation. It also shows high P5CS expression (key enzyme in proline synthesis) in esk1 before and after acclimation and after acclimation in WT.

Front 31

Describe experiments with sfr4 mutant

Back 31

sfr (sensitive to freezing) mutants are unable to cold acclimate. Unlike WT they do not accumulate sucrose levels in response to cold they fare much worse that WT with a much higher LT50 after the conventional acclimation and freezing however if you add sucrose they do much bettwe. Shows sucrose is needed to protect against abiotic stress and freezing.

Front 32

What are COR genes?

Back 32

cold regulated genes which are activated at temps between 2-6degrees and encode products which bring about regulation. They can be regulated or down-regulated twice as many are up-regulated as are down-regulated

Front 33

Describe regulation of COR genes

Back 33

The CRT gene promoter motif is bound to by CBF transcription factors in response to cold eg CBF1 protects against chilling induced oxidative stress by induxing the transcription of catalyse (CAT1) which destroys H2O2.
1st step in signalling mechanisms that CBFS are a part of is an increase in cytosolic calcium levels.

Front 34

Describe heat tolerance

Back 34

All organisms have a level of innante heat tolerance this is known as basal thermotolerance. All organisms also have the ability to acclimate to even higher temperatures rapidly known as acquired thermotolerance

Front 35

Why are plants not tolerant to high temps from the offset?

Back 35

Firstly, would be energetically costly
secondly, processes such as saturating membrane reduces ability to survive in cooler temperatures

Front 36

Examples of acquired thermotolerance

Back 36

Soya bean: those acclimated at 40degrees before 45 grow substantailly higher than those who havent
Arabidopsis : acclimated plants who've had 1.5hours at 38degrees before 2hours at 45 degrees survive. Those which havent die.
hydrated plants are more affected by increased temps, dehydrated tissues such as seeds and pollen remain viable at much higher temperatures.

Front 37

Describe the effect of heat stress on photosynthesis and respiration

Back 37

Photosynthesis is inhibited first (at lower temps) leading to reaching compensation point where CO2 used by photosynthesis equals that produced by respiration. Carbon sources aren't replaced and stores/reserves are depleted so the plant breaks down proteins etc 'autophagy' (eating itself)
High temps also means ion leakage

Damages membranes therefore disrupts electron transport chain.

Front 38

Give evolutionary adaptations to high temps

Back 38

Craterostigma plantagineum RESSERECTION PLANT is native to Namibia and South Africa . In summer leaves dry and shrink (heat has less effect on dehydrated tissues) It then ''resserects'' and rehydrates in winter. The cytoplasm contains the 8 carbon octalose which preserves oraganelles and enzymes whilst the plant is dessicated.
Symbiosis with fungi: 3 way symbiosis between virus inside fungi inside plant protects against heat. Different plants eg tomato plant can be innoculated with the fungi and virus to protect it. Area of research but expression profile of genomes analyses of some candidate genes suggest possible involvement of osmoprotectants such as trehalose, glycine betaine, and taurine in the heat stress response.

Front 39

Physiologcal avoidance/acclimation of heat tolerant plants

Back 39

Leaf orientation
Fatty acid composition
Transpirational cooling - NOT USEFUL IN PLACES OF DROUGHT
Production of antioxidants

Front 40

Cellular acquisition of thermotolerance

Back 40

The heat shock response.

This is important in acquired thermal tolerance, its v conserved across prokaryotes to euakryotes (plants, animals, fungi and bacteria). proteins are sensitive to disrrutption by changes in temperature, pH or ionic strength. Molecular chaperones physically interact with other proteins to deal with protein unfolding because of the heat.
Heat shock factors bind to heat shock elements in the DNA to regulate transcription of heat shock protein mRNA.

Front 41

Give the classes of HSP/ Chaperones

Back 41

Hsp100 - ATPase; protein disaggragation
Hsp90 - ATPase; protein conformation
Hsp70/DNAK - ATPase; nascent protein folding
Chaperonins (GroE, Hsp60) ATPase, nascent protein folding
Small Hsps - prevent irreversible protein aggragation

CLASSIFIED BY SIZE

Front 42

Describe action of Hsp101

Back 42

In response to heat AtHsp101 forms a hexameric complex and uses ATP to fold the denatured aggregated proteins

Front 43

Describe HSF regualtion of HSP

Back 43

In the unstressed cell, HSF is maintained in a monomeric non-DNA binding form by interactions with HSP70
Upon heat shock HSF assmebles into a trimer
HSF trimers bind to the heat shock element in gene promoters
Bound the HSF protein becomes phosphorylated trasncriptional activation of heat shock genes leads to increased levels of HSP70 which binds HSF dissocaites trimer to monomer

Front 44

Whats the structure of chaperone proteins?

Back 44

Extremely thermostable, lots of di-sulfide bridges.