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