Lecture 8 - Plant Responses to Water Stress Flashcards
how is water potential measured in the xylem
scholander pressure chamber
cohesion tension theory
water forms a string of water molecules molecules during its movement through the xylem
what happens when a twig is cut from a plant in the xylem
air enters the cut tracheary element because the tension is cut in the string of water molecules
what happens to the cut twig from a plant if it is put into a pressurized chamber
the air-water interface in the mesophyll is pushed back into the original position. the water moves back into the cut element
a high value of pressure means a ______ value of tension and a _____ degree of water stress
high, high
what does the pressure-volume curve show
when the relative water content is high (turgid vacuole), the pressure is high. When the volume is low (flaccid, the pressure decreases
plant response to water stress depends upon:
a) imposed conditions
b) genetic background
c) physiological status
what causes plant responses to water stress to vary
extent of water deficit, rate of dehydration, and by genotype
when do plants respond to a water deficit
after a critical soil water potential is reached
________ and _________ affect plant response and survival
rate of water deficit and genotype
difference between sensitive species and resistant species to fast rate of water loss
sensitive species: will experience a lot of injury
resistant species: suffer less damage
why does slow rate of water loss reduce injury
it allows plants time to respond and avoid injury
osmotic adjustment
a lowering of solute (osmotic) potential due to net solute accumulation in response to drought stress
how does osmotic adjustment help with turgor regulation in drought
- it maintains water absorption and cell turgor in drought conditions
- sustain higher photosynthetic rate and expansion growth under drought
what is the cell wall made of
hemicellulose, cellulose microfibril, pectin, and structural protein
elastic adjustment of the cell wall
the relationship between cell volume and turgor
what does increased cell wall elasticity (softening) do
delays the loss of turgor
order of reactions to water stress
perception - signaling - responses
short term responses to water stress
- decrease in stomatal conductance
- alterations in hydraulic conductivity
- osmotic adjustments
- elastic adjustments
long term responses to water stress
- induction of drought-induced genes
- changes in growth rate including root architecture
how does a water deficit affect growth rate
reduces crop growth and yield
water/resources are preferentially allocated to the root
what does the adaptation of roots to water deficit depend on
severity and genotype
what are some adaptions of roots to water deficit
- root hair elongation
- increase in number or diameter of xylem elements
- increase in hydraulic conductance through aquaporins
plants have to balance their ____ and _____ responses
growth and survival
survival responses to drought
- stomatal closure
- limitation of shoot growth
- diversion of carbon and energy to storage and biosynthesis of protective compounds
growth responses to drought
- reprogramming of energy metabolism
- osmotic adjustment
- maintained cell wall flexibilty
what plant responses increase in water deficit
solute accumulation and root growth
what plant responses decrease in water deficit
photosynthesis, stomatal aperture, shoot meristem and leaf growth, and water uptake
