Water Relations

Question 1

Primary root

Answer 1

First organ to originatebfrom seed embryo

Question 2

Secondary roots

Answer 2

Lateral roots

=> further anchoring
=> & uptake of water and nutrients

Question 3

3 steps of water uptake

Answer 3

Uptake
Transport
Transpiration

Question 4

Water

Answer 4

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

Question 5

Diffusion

Answer 5

Movement from subst. from high to low conc.

=> 2nd law of thermodynamics => stabilize env.

Question 6

Diffusion (equations)

Answer 6

1st Fick’s law
Diffusion rate is proportional to concentration gradient

2nd Fick’s law
Diffusion time is proportional to square diffusion distance

Question 7

Efficiency of Diffusion

Answer 7

Only in short distance

=> in large distances: additional force => Bulk flow

Question 8

Bulk flow

Answer 8

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

Question 9

Osmosis

Answer 9

Diffusion of water through semipermeable membrane

Question 10

Osmotic potential

Answer 10

-RTc (c= osmolarity mol/L)

Pure water => psi (osmotic potential) is 0
Dilution of sth in water = reduction of psi

Question 11

Water potential

Answer 11

Psi w = psi s + psi p + (psi g)
s = osmotic pressure
p = hydrostatic pressure (+ = turgor, - = tension (as in xylem))

Question 12

Water flows

Answer 12

Passively (through osmosis) to area of lower psi

Question 13

Deplasmolyse

Answer 13

Turgor
Pressure potential > 0

Question 14

Plasmolyse

Answer 14

Pressure pot = 0

Question 15

soil composition

Answer 15

Small particles enable vertical movement => better retention of water

Question 16

Wilting point and field capacity

Answer 16

Point at which plants wilt and don’t recover and level above which soil can not take up more water

Determined by soil composition

Question 17

Zones of root

Answer 17

Meristematic, elongation and maturation

Question 18

Symplastic pathway

Answer 18

Through plasmodesmata

Question 19

Suberin

Answer 19

Kork
Water impermeable
In casparian strip

Question 20

Aquaporins

Answer 20

6 transmembrane domains
Form tetramers
Encided by multigenic family
Highly regulated
Do not only transport water => e.g. ROS

Question 21

Xylem

Answer 21

Tracheids or vessel elements

Question 22

Pressure gradient per meter

Answer 22

Psi p/delta x

Question 23

Cohesion tension theory

Answer 23

Tranpiration of water leads to lower water potential => transpirationssog durch cohäsion

Question 24

Water loss

Answer 24

Mostly through transpiration => transport
Only very few percent directly used for photosynthesis & metabolic reactions/ growth

Question 25

Reaction to dessication

Answer 25

Mesophytes: osmolytes LEA dehydrins ROS-detoxification Xerophytes: cytoplasmic vitrification leaf shrinkage or folding protection of photopigments vacuolar shrinkage increase in antioxidant systems

Question 26

Xerophyte adaptions

Answer 26

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

Question 27

Anatomical traits of Xerophytes

Answer 27

succulent (water storing leaves or stems) thick cuticle sunken stomata

Question 28

Water deficit Perception

Answer 28

cell turgor membrane potential ROS osmotic content others... => in plasma membrane (receptor kinases, channels and proteins like integrins)

Question 29

Water deficit signaling

Answer 29

Between cells: ABA ethylene Hydraulic signals Water potential Xylem pH Other signals... Within cells: ABA ROS transcriptional cascades other signals...

Question 30

Water deficit Responses

Answer 30

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

Question 31

ABA impacts

Answer 31

Ion channel activity Transcription factor activation

Question 32

Two possible responses to drought

Answer 32

ABA pathway Or direct activation of transcription factors

Question 33

Cellular responses to desiccation

Answer 33

Shrinkage Shriveled membrane Fragmented vacuole Reactive oxygen species can accumulate Proteins can aggregate and denature

Question 34

Osmolites

Answer 34

Proteins and sugars that are able to maintain an aqueous environment around other active proteins

Question 35

LEA

Answer 35

late embryo abundant proteins intrinsically disordered Not properly folded Bind to other proteins to protect them

Question 36

ROS accumulation

Answer 36

Result of stopping photosynthesis Reduction of chlorophyll releases electron => produces ROS => very reactive => damage proteins and membrane

Question 37

ROS detoxification

Answer 37

Number of diff enzymes produced (Superoxiddismutase, Catalase, Ascobate peroxidase) These systems are upregulated under water stress conditions

Question 38

Aquaporin regulation

Answer 38

Expression Localization (compartments or membrane) Activity/gating => by phosphorylation or binding of calcium

Question 39

ABA perception

Answer 39

PYR1/RCAR receptor Upon binding of ABA it inhibits phosphatases If receptor is inactive => phosphatase dephosphorylates SnRK kinases (can phosphorylate TFs and Ion channels)

Question 40

Root growth direction

Answer 40

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