Water Relations Flashcards
Primary root
First organ to originatebfrom seed embryo
Secondary roots
Lateral roots
=> further anchoring
=> & uptake of water and nutrients
3 steps of water uptake
Uptake
Transport
Transpiration
Water
Polar solvent
=> mean of transport for solute
Medium and partner for biochemical reactions
Property of
Cohesion => attraction btw molecules => transpiration column
Adhesion => attraction to surface
Enables
Turgor: Stature & Growth
Temp regulation
Yield
Diffusion
Movement from subst. from high to low conc.
=> 2nd law of thermodynamics => stabilize env.
Diffusion (equations)
1st Fick’s law
Diffusion rate is proportional to concentration gradient
2nd Fick’s law
Diffusion time is proportional to square diffusion distance
Efficiency of Diffusion
Only in short distance
=> in large distances: additional force => Bulk flow
Bulk flow
Concerted movement of molecules en masse most often in response to a pressure gradient
Poiseuille’s equation
Volume flow rate depends on radius of vessel
Osmosis
Diffusion of water through semipermeable membrane
Osmotic potential
-RTc (c= osmolarity mol/L)
Pure water => psi (osmotic potential) is 0
Dilution of sth in water = reduction of psi
Water potential
Psi w = psi s + psi p + (psi g)
s = osmotic pressure
p = hydrostatic pressure (+ = turgor, - = tension (as in xylem))
Water flows
Passively (through osmosis) to area of lower psi
Deplasmolyse
Turgor
Pressure potential > 0
Plasmolyse
Pressure pot = 0
soil composition
Small particles enable vertical movement => better retention of water
Wilting point and field capacity
Point at which plants wilt and don’t recover and level above which soil can not take up more water
Determined by soil composition
Zones of root
Meristematic, elongation and maturation
Symplastic pathway
Through plasmodesmata
Suberin
Kork
Water impermeable
In casparian strip
Aquaporins
6 transmembrane domains
Form tetramers
Encided by multigenic family
Highly regulated
Do not only transport water => e.g. ROS
Xylem
Tracheids or vessel elements
Pressure gradient per meter
Psi p/delta x
Cohesion tension theory
Tranpiration of water leads to lower water potential => transpirationssog durch cohäsion
Water loss
Mostly through transpiration => transport
Only very few percent directly used for photosynthesis & metabolic reactions/ growth
Reaction to dessication
Mesophytes:
osmolytes
LEA
dehydrins
ROS-detoxification
Xerophytes:
cytoplasmic vitrification
leaf shrinkage or folding
protection of photopigments
vacuolar shrinkage
increase in antioxidant systems
Xerophyte adaptions
Phenological: only grow/reproduce after rain, otherwise remain quiescent
Morphological: deep roots, high xylem transport/tissue storage, tiny or absent leaves
Biochemical: CAM metabolism
Anatomical: thick cuticle, rolled leaves, stomatal crypts
Anatomical traits of Xerophytes
succulent (water storing leaves or stems)
thick cuticle
sunken stomata
Water deficit Perception
cell turgor
membrane potential
ROS
osmotic content
others…
=> in plasma membrane (receptor kinases, channels and proteins like integrins)
Water deficit signaling
Between cells:
ABA
ethylene
Hydraulic signals
Water potential
Xylem pH
Other signals…
Within cells:
ABA
ROS
transcriptional cascades
other signals…
Water deficit Responses
Short term:
Decrease in stomatal conductance (close)
Alterations in hydraulic conductivity
osmotic adjustments
Long term:
induction of drought-induced genes
changes in growth rate and root architecture
ABA impacts
Ion channel activity
Transcription factor activation
Two possible responses to drought
ABA pathway
Or direct activation of transcription factors
Cellular responses to desiccation
Shrinkage
Shriveled membrane
Fragmented vacuole
Reactive oxygen species can accumulate
Proteins can aggregate and denature
Osmolites
Proteins and sugars that are able to maintain an aqueous environment around other active proteins
LEA
late embryo abundant proteins
intrinsically disordered
Not properly folded
Bind to other proteins to protect them
ROS accumulation
Result of stopping photosynthesis
Reduction of chlorophyll releases electron => produces ROS => very reactive => damage proteins and membrane
ROS detoxification
Number of diff enzymes produced (Superoxiddismutase, Catalase, Ascobate peroxidase)
These systems are upregulated under water stress conditions
Aquaporin regulation
Expression
Localization (compartments or membrane)
Activity/gating
=> by phosphorylation or binding of calcium
ABA perception
PYR1/RCAR receptor
Upon binding of ABA it inhibits phosphatases
If receptor is inactive => phosphatase dephosphorylates SnRK kinases (can phosphorylate TFs and Ion channels)
Root growth direction
Xerobranching (avoid desiccated areas)
Hydropatterning (grow lateral roots toward water)
Xerotropism (elongation along verical gradient)
Hydrotropism (elongation along horizontal gradient (neigung))
Primary root elongation
Preferential lateral root proliferation in deep soil
Production of short lived, drought induced lateral roots
Increase root hairs & their length & aquaporins
