ACCLIMATIONS TO ABIOTIC STRESS (1) Flashcards
Describe morphological and physiological acclimations to abiotic stress. Explain how cellular acclimation enhances avoidance and tolerance to heat and water 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
> transpiration
photosynthesis
Stomata close and open depending on environmental conditions and time of day. Transpiration from open stomata varies with temperature, humidity, wind speed…
influx of ions > water influx > increase in guard cell turgor
STOMATAL MOVEMENT UNDER ABIOTIC STRESS
Water stresses:
> soil water deficit
> high soil salinity
> cold
Stomatal closure during water stress limits rapid 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 heep the leaf cooler.
MORPHOLOGICAL ACCLIMATIONS TO WATER STRESS
low humidity - water deficit osmotic stress
. shoot growth inhibition
. senescence of old leaves
–» limit evaporation area
. sustained root growth
. increased root/shoot ratio
–» increase absorption area
Under mild water stress, rapid shoot growth inhibition is not caused by reduced photosynthesis.
Possible explanations for shoot growth inhibition:
. heep resources for acclimation
. not enough water influx for cell growth
. limit transpiration area
on the long term, decreases photosynthesis will limit growth
OSMOTIC ADJUSTMENT
Acclimation of solutes (osmolytes) increased cellular osmotic potential and facilitates water uptake and the maintenance of cell turgor.
OSMOTIC ADJUSTMENT: compatible solutes
Compatible solutes can be accumulated without impairing cellular functions. They include sugars, sugar alcohols, amino acids, and betaines.
The type and contribution of different compatible solutes are highly dependent on the species.
PRODUCTION OF COMPATIBLE SOLUTES
Glycine betaine biosynthetic pathway…
Increased expression of biosynthetic enzymes under stress controls the accumulation of osmolytes.
Proline biosynthetic pathway…
Synthesis of compatible solutes can contribute to maintaining root growth.
Proline content of Arabidopsis roots at low water potential in WT and proline synthesis mutants.
Arabidopsis seedlings growing on control or PEG infused agar plates
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
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
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
DIFFERENT SENSITIVITY TO STRESS OF PLANT TISSUE
Sensitive tissue:
. young/growing tissues (seedlings, meristems, primordia)
. reproductive organs
Tolerant tissues;
. seeds
acclimated tissue (already experienced or expecting stress)
ABIOTIC STRESS CAN AFFECT FLOWERING TIME
Salt stress delays flowering tie under long days in Arabidopsis.
Phosphate deficiency induced flowering under long days in Arabidopsis.
The effect of drought on flowering time in Arabidopsis depends on daylength.
THE FLOWERING RESPONSE DEPENDS ON LOCAL ADAPTATION
Effect of low nutrient availability on flowering time in different ecotypes of Arabidopsis under long days.
Nutrient deficiency does not delay flowering for all ecotypes.
ABIOTIC STRESSES CAN AFFECT FLOWERING TIME
The effect of a given abiotic stress on flowering time are difficult to predict and generalise:
. depends on the environment the plant is adapted to
. depends on the conditions the plant is growing in (e.g. daylength)
. depends on the characteristics of the stress
