Week 10 Flashcards
What is stress?
An external factor that exerts a disadvantageous effect on a plant
What is used to measure stress?
Survival
Crop yield
Biomass
Carbon or mineral uptake
What impacts stress tolerance?
Adaptation - geneticallly determined tolerance
Acclimation - increase in tolerance in reponsing to pre-exposure
What are the 2 types of stress?
Abiotic and Biotic
What are abiotic stresses?
Water deficit, salinity, temperature, O2 deficiency, light intensity and UV light
What are biotic stresses?
Microbial pathogens, pests, weeds and parasitic plants
How much does impact does stress have on crop yields?
Abiotic stress reduces US crop yield to 22% of genetic potential
What does water deficit mean in context of plants?
Any water content of tissue below that of th emost hydrated tissue
What is the developmental reponse to water deficit?
Decrease in leaf expansion and number
What is the relationship between rate of expansion, turgor pressure Y(Psi greek letter)p and extensibility (m)?
Rate of expansion is directly proportional to turgor pressure and extensibility
What is turgor pressure?
The pressure that pushes the plasma membrane against the cell wall
What happens in a plant to show the relationship between rate of expansion, turgor pressure and extensibility?
Decreased cellular water content –> lower turgor pressure
Lower turgor pressure –> decreased cell expansion
Decreased cell expansion –> decreased leaf size
Decreased leaf size –> decreased transpiration
How can indeterminate plants responsed to a water deficit?
Leaf number may also be reduced
What is important about detetcting decrease in cell expansion?
Decrease in expansion is an early indicator of water deficit, but the protective effects are quite slow (developmental)
What is the response in roots to water deficit?
Roots are stimulated to grow
What determines the biomass: shoot ratio?
Water avaliability
What growth is favoured when photosynthetic capacity exceeds water avaliability?
Root growth is favoured
What growth is favoured when photosynthetic capacity is lower than water avaliability?
Shoot growth is favoured
How do roots grow different in water deficit environments?
Soils tend to dry from above and plants respond to water deficit by directing photosynthate to downward root growth
What is a response found in the overall leaf when water in a deficit?
Stimulation of leaf abscission (leaf detachment)
What is the formula for total leaf area?
Total leaf area = number of leaves x surface area of a leaf
What happens with abcission for transpiration levels?
Abscission results in decreased transpiration
What is a rapid response to water deficit in plants with respect to solar radiation?
They reduce the absorption of solar radiation
How do plants reduce absorption of solar radiation in water deficit condtions?
The movement of leaves leads to the reduction of the absorption of solar radiation which decreased transpiration
What other adaptations lead to the reduction of solar radiation?
Reflective cuticular waxes and leaf hairs
How do plants rapidly stimulate the closure of stomata in water deficit conditions?
This is mediated by abscisic acid (ABA)
How does abscisic acid (ABA) lead to closure of guard cell?
ABA, which is made in mesophyll cells, moves into the apoplast then onto the guard cell and induces guard cells to become more flaccid.
How does ABA get to the guard cell to become flacid?
It causes ions to be actively pumped out (ion efflux) and inhibition of ion influx
How can plants make osmotic adjustments in water deficit conditions?
Increased cellular solute concentration leads to decreased water potential Psi(Y)w, facilitating absorption of water from the soil (water is absorbed as long as water potential is more negative than that of soil) and allowing extraction of water that is more difficult to extract
What molecules are produced to adjust osmotic levels in water deficit conditions?
Sugar alchohols like sorbitol
Amino acids like proline
quaternary ammonium compounds like glycine betaine
Tertiary sulfonium compounds (TSCs) like 3-dimethylsulfoniopropionate (DMSP)
What is the collective name of the molecules produced by the plants to lower leaf water potential?
They are known as compatible solutes
How many genes are induced in water deficit condtions?
Microarray experiments indicate that ~105 of all genes are induced
What are examples of type of genes with change in conditions in water deficit conditions?
Aquaporins —> water transport
Proteases —> Degradation of denatured proteins
Betaine aldehyde dehydrogenese —> Glycine betaine synthesis
What other conditions also induce many of the same genes as in water deficit?
Cold and salt stress
What are the two different pathways for gene expression response to osmotic stress?
ABA-dependant pathway and ABA-independant pathway
What is an example of a gene that changes with osmotic stress?
DREB1/DREB2 (drought response element binding proteins), both in ABA dependant and independant pathway, which codes for DRE (drought response elements) which impacts tolerance
What is the maximum temperature that most plants can survive?
Most plants can’t survive greater than 45 degree celcius temp for extended periods
How does water deficit contribute to heat stress?
Reduces transpiration and thus cooling
How does heat kill plants?
Increased membrane fluidity –> loss of membrane function
How does heat impacted inner plant processes?
Photosynthesis and respiration are inhibited, photosynthesis first then respiration
What happens to CO2 in a plant when the temperature is higher than temperature compensation point?
CO2 production exceeds CO2 fixation and there is a net loss of carbon
How can plants respond to heat stress?
Leaf movements (like water deficit)
Synthesis of heat shock proteins (HSPs)
How long after an abrupt temperature shift will mRNAs appear?
3-5 minutes
What causes more mRNA quickier abrupt or gradual temperature rise?
Abrupt
What is the function of HSP60, 70, 90, 100?
They are molecular chaperons, proteins that refold unfolded (denatured) proteins
What does the number next to the HSP mean?
It is the rough size of protein in kDa
What induces the proteins to be made?
Cold and osmotic stress
How does HSP70 act as a master gene?
The protein binds to a protein called heat shock factor.
When it gets hot HSP70 is released.
The heat shock factor triggers the other proteins to be made.
When temp cools down HSP70 rebinds to heat shock factor silencing the gene production of HSP.
What happens to heat shock factor in hot temps after dissciating HSP70
Three HSF join together, making them active which causes them to trigger heat shock genes
What is chilling stress?
Temperature too low for normal growth but no ice formation
What are chilling sensitive crop species?
Maize, french bean, rice, tomato, cucumber and cotten
What are common chilling injuries?
Discolouration, lesions, water soaking, wilting
How does chilling impact membrane function?
Decreased membrane fluidity –> loss of membrane function
What are chilling injuries on a biochemical level?
Impacts on:
Photosynthesis
Translocation
Respiration
Protein synthesis
Protein degradation
What do chilling sensitive plants have in their membrane?
High % of saturated membrane fatty acids as seen in Arabidopsis fab1
What do chilling resistant plants have in their membrane?
Low % of saturated membrane fatty acids
How does freezing temps impact plants?
Dehydrates cells as water outside freezes so water from within cell leaves the cell
How can plants acclimatise to freezing temps?
The production of ABA as seen in Alfalfa which can withstand upto -10 degrees c
What happens if a plant is ABA insensitive or deficient?
They do not acclimate to freezing, though deficient can acclimatise by ABA treatment
How many genes respond to freezing?
More than 100 genes
What are examples of cold resistance gene products and their function?
Antifreeze products –> inhibit ice crystal formation
Heat shock proteins –> Renaturation of denatured proteins
LEA (late embryogenesis abundant) proteins –> Water binding, membrane stabilisation
Why are many of the genes involved in water deficit and cold response the same?
They are both osmotic stresses
What is similar with CBF/DREB proteins?
They are the same
What is phenology?
The study of periodic natural biological phenomena controlled by climate
Why is seasonal alignment important in plants?
It is important for different developmental transitions with misalignment of floral transitions having fatal consequences
How do plants know what season they are in?
Due to similar nature of some seasons there is a requirement for exposure to a prolonged period of cold to help ensure spring-time flowering
Why is plants needing a prolonged period of cold to flower important for humans?
A cold requirement promoes spring flowering is an important agronomic trait
How have humans impacted crops cold requirements?
Crop varieties have been bred with different levels of cold requirement
What happens if a plant has insufficient cold?
Insufficient cold for varieties with long chill requirement delays flowering and impairs yield
What did Trofim Lysenko investigate?
The effetcs of temperature variation on the life-cycle of plants
What did Trofim Lysenko realise about the results of his research?
That winter wheat plants would flower faster if he first exposed water-soaked (imbided) seeds to prolonged cold before sowing
What did Trofim Lysenko name this process?
‘jarovization’ but was later translated into ‘vernalisation; from the latin vernum meaning spring
What did Trofim Lysenko observe in his experiments?
A quantitative effect of prolonged cold exposure
Longer cold periods progressively reduced the time taken for the wheat plants to flower
What were the tragic results of the beliefs and usage of Trofim Lysenko?
He convinces Stalin and other political leaders of incorrect ideas.
He believed that winter wheat grain vernalisation fully converted it to a spring wheat variety - no cold requirement for future progeny
All fundamental genetic and cytological findings reported by western scienstists were incorrect and should be rejected
What was the consequence of Trofim Lysenko’s pseudoscience?
Lysenkoism contributed to the Russian famine of 1921-1922 and the Chinese famine of 1959-1962. These caused more than 20 million deaths
Who and when gave the formal definition for vernalisation?
French botanist Pierre Chouard in 1960
What is the function of the gene/ protein FLC?
A MADS-Box trancription factor that binds to the promoters of flowering genes and inhibits their transcription
What does FLC expression meaning for plant flowering?
FLC expression = Delayed flowering
What gene can increase FLC regulations?
The gene FRIGIDA (FRI). FRI upregulates FLC
What happens to fri mutant plants?
Low FLC expression = flowering is repressed until plants are competent
What does prolonged cold do to the FLC gene?
Prolonged cold gradually silences FLC expression. This means rapid flowering under permissive conditions
Why can’t simple gene regulation provide a long term memory of cold?
Perception of long term, reducing, fluctuaitng temperatures is requried
Requirement of a “counting” mechanism
Requirement of a “memory” component
This process must be reset for the next generation
This process must be robust
What causes the cold registration of the FLC gene?
This is achieved via epigentic changes
What is epigenetics?
Any potentially stable and heritable change in gene expression that occurs without a change in DNA sequence
What is the function of DNA methylations?
Associated with gene silencing
What happens with heterochromatin?
Transcription is repressed
What happesn with euchromatin?
Transcription is active
What are nucleosomes mostly consisted of?
Histones
What can modify histone tails?
Methylation (Me), Acetylation (Ac), Ubiquitination (Ub), Phosphorylation (P), Sumoylation (Su)
What happens to the chromatin structure when histone proteins are modified?
This will modify the chromatin structure ie open or close it
Where on each histone monomer does modification happen?
The amino terminal regions of the histone extent beyond the nucleosome and are accessible for modification
What can happen at Histone H3 when it comes to modification?
The amino terminus of H3 is often modified at one or more positions, which can contribute to an activation or inhibition of transcription
What are the active marks FRIGIDA can modify to upregulate FLC transcriptions?
H3K36me3 and H3K4me3
What are the repressive marks cold weather can modify to down regulate FLC transcriptions?
H3K27me3
What are the chances of cold exposure inducing FLC switching off?
There is a low probability of FLC in each cell from switching form an on to an off state
How does the off state propagate?
The off state is propagated to daughter cells after each cell division
What determines the barrier for flower intiation?
The proportion of cells that remain stably silenced dtermine the barrier
How does cold exposure prevents FRI from binding to FLC promoters?
During cold, FRI is sequestered away form FLC loci into nuclear condensates preventing FRI from binding to FLC promoters and enhancing transcriptions
What does the long noncoding RNA COOLAIR and the cold induced protein VIN3 do?
They recuit the PHD PRC2 Complex to the FLC gene, this activates FLC silencing vio H3K27me3 modificaiton
What happens to FRIGIDA in the autumn?
FRIGIDA activates high FLC expression preventing warm periods from activating flowering genes
What happens to the chemical for vernalisation in the winter?
An increase in antisense Inc RNA, coolair transcription, FRIGIDA protein condensates form in the nucleus
What happens to the FLC loci over time?
Gradually, H3K26me3 acive marks are lst across individual FLC loci.
A switch to H3K27me3 repressive marks is coordinated by Inc RNA COOLAIR
What happens with vernalisation in the spring?
LHP1 ensures stable H3K27me3 coverage that maintains FLC repression over many cell divisions. PErmissive conditions in spring can then activate flowering gene eg FT
Why is FLC reactivated during seed development?
To ensure the next generation inherits a vernalisation requirement
What is the main contributer to flowering time variation?
Approximately 70% of flowering time variaiton has been attributed to alleleic variation of FRIGIDA, much of the remaining 30% to FLC itself and its regulators
Where have slow vernalisation traits evolved?
In locations with long, harsh winters. The slow vernalisation trait maps to cis polymorphorphism within the FLC gene
How is slow vernalisation traits shown in the Lov1 varients compared to the lab Col FRI varient?
After 4 weeks the Col FRI FLC will decrease allowing for flowering in warm weather. Compared to Lov1 which wont flower as it needs 12 weeks
When does the Lov1 variet vernalise?
It vernalises during the autumn, which has temps that match up with the ideal vernalisation range of -3.5 to 6 degrees C. The plants hibernate during winter instead.
Where does Lov1 mutant live?
Northern sweden
