Acclimation 1 rewatch Flashcards
Describe Adaptation to stress
Describe Acclimation to stress
Adaptation to stress: heritable modifications in structure or function that increase fitness/productivity in a stressful environment
Acclimation to stress: non-heritable physiological modifications that occur within the life of an individual, induced by gradual/repeated exposure to stress
Transpiration and stomata
Stomata close and open depending on environmental conditions and time of day. Transpiration from open stomata varies with temperature, humidity, wind speed etc.
Influx of ions –> water influx –>increase in guard cell turgor
heat and water stress together are very bad mostly water loss will be prioritised
Stomatal movement under abiotic stress
Describe some water stresses
Soil water deficit
High soil salinity
Cold
Stomatal closure during water stress limits rapidly water loss but also reduces CO2 uptake, which slows down the Calvin-Benson cycle.
If stomata can be kept open during heat stress (no water stress), evapotranspiration will help keep the leaf cooler.
Morphological acclimations to water stress
Low humidity
Shoot growth inhibition
Senescence of old leaves
→ limit evaporation area
Water deficit/stress
Osmotic stress
Sustained root growth
Increased root/shoot ratio
→ increase absorption area
Rate of leaf elongation and net photosynthesis at varying soil water potentials in maize
Under mild water stress, rapid shoot growth inhibition is not caused by reduced photosynthesis.
Possible explanations for shoot growth inhibition:
Keep resources for acclimation
Not enough water influx for cell growth
Limit transpiration area
In the long term, decreased photosynthesis will limit growth.
as you decrease water, there is a decrease in shoot elongation. Plant stops putting resources in short growth also limiting area for transpiration. (Growth requires water)
Model of shoot growth response to gradual salt stress
As salt stress is added there is an extra effect called the salt specific effect as ions accumulate in the plamnt ans have a toxic effect. Only some plants may be tolerant to this. This will decrease the shoor rate even more. This could be due to Efficient cellular acclimation to salt or Little cellular acclimation to salt
Elongation rates of the primary root (steady rate) and shoot (maximum rate after transplanting) of seedlings at varying water potentials
Not all species will share same effect of stress.
(more negative more intense wter stress) So more stress. The plant on the graph that shows the best acclimation to this stress (root:shoot ratio) is
Find lines that the most distant from eachother=soybean
Osmotic adjustment
Accumulation of solutes (osmolytes) lowers cellular osmotic potential and facilitates water uptake and maintenance of cell turgor.
A way to retain water and have a continual uptake of it. Helps maintain turgor
If you don’t do any osmotic adjustment you will have plasmolysis (wilt)
Osmotic adjustment: compatible solutes
Compatible solutes can be accumulated in high quantities without impairing cellular functions. They include sugars, sugar alcohols, amino acids and betaines.
The type and contribution of different compatible solutes is highly dependent on the species.
Different species may have a different mix of compounds that are compatible. Some have certain preferences e.g in tobacco its mostly proline. In rice its mostly sugars.
Production of compatible solutes
Glycine betaine biosynthetic pathway
Glycine betaine biosynthetic pathway
molecule goes to choline monooxygenase (CMO) –> betaine aldehyde dehydrogenase (BADH)–> glycine betaine
Increased expression of biosynthetic enzymes under stress controls the accumulation of osmolytes.
when people measured expression of genes under salt stress they found that there was more expression (mRNA) in the plant than in control plants.
Proline biosynthetic pathway
glutamate with (P5CS) [limiting step]–> glutamate semialdehyde then (spontaneous cyclization)–> pyrroline-5-carboxylate then (pyrroline-5-carboxylate reductase)–> proline
Synthesis of compatible solutes can contribute to maintaining root growth
Is proline an important part in maintaining root growth under osmotic stress?
Proline content of Arabidopsis roots at low water potential in WT and proline synthesis mutants
PEG is polyethanol glycine (creates osmotic stress)
Osmotic adjustment: inorganic ions
Inorganic ions are NOT compatible solutes, they are toxic at high concentrations, so they need to be compartmented into the vacuole.
you neeed to have abalance between inorganic ions the vacuole and the cytoplasm so you need compatibe ion in the cytoplasm. Mot water will go into the vacuole
Protection/repair compounds
Under stress conditions, heat shock proteins/chaperones can:
Stabilise proteins and membranes
Refold denatured proteins
Assist with degradation of damaged proteins
Prevent aggregation of proteins
Disaggregate proteins
they have a protect and a repair aspect these both have different heat shock proteins. HSP can also help give proteins shape even with no stress
Late embryogenesis abundant (LEA) proteins
Late embryogenesis abundant (LEA) proteins are quite small, highly hydrophilic with little secondary structure.
Synthesised in high quantities in embryos
Accumulate during water stress
Protective effect on cellular components
they are randomly coiled. Stress is what gives them their shape. Desiccation gives alpha helix shape. They make filaments to prevent cells from being fully dessicated and loose their shape.
They help prevent dessication in seed also.
