Plant water regime Introduction Adaptation, acclimation Poikilohydric and homoiohydric plants Water content, relative water content Water potential and its components Water and growth

Basic characteristics Water content WC [%] = (FM - DM / FM)  100 FM - fresh mass, DM - dry mass cytoplasm %, chloroplasts, mitochondria about 50 %, ripe fruits %, leaves %, roots %, wood 50 %, seeds, pollen grains % Relative water content RWC [%] = [ 1 - (FM s - FM a )/(FM s - DM) ]  100, FM s - mass after saturation, FM a - actual fresh mass Plant water balance = absorption - transpiration Effects of soil moisture and relative humidity

Water potential and its components  w = (  w -  w 0 ) / V w  w - water potential,  w - chemical potential of water in the system,  w 0 - chemical potential of pure water, V w- - volume per mole of water  = (  G /  n i ) T,p,nj G - Gibbs free energy, n i - number of moles of component i, nj - number of moles of other components, T - absolute temperature, p - pressure  w =  s +  p +  m +  g  s - osmotic potential,  p - pressure potential,  m - matric potential,  g - gravitational potential  s = (RT / V w ) ln a w = -cRT R - gas constant, a w - water activity, c - concentration  = V (  p /  V)  - volumetric modulus of elasticity, V - cell volume Differences in  w and its components inside cells and in apoplast (  wall a  tissue )

Methods of determination  w - psychrometric methods, pressure bomb  s - psychrometric and cryoscopic methods  p - pressure probe Thermocouple psychrometer

Pressure chamber

Pressure probe

uplatnění Hofler diagram The roles of individual components:  g - high trees  m - imbibition and germination (till water content about 60 %)  p - veins, apoplast, growth, movements of stomata  s - transport on cell and tissue level, plasmolysis, plasmoptysis, root pressure, osmotic adjustment, growth

Osmotic and elastic adjustment Osmotic and elastic adjustment (growth, drought, salinity, low temperature, etc.), induction by decrease in soil water potential, air humidity, etc. Osmotic adjustment – ion uptake, production and accumulation of osmotically active substances such as sugars (glucose, trehalose, saccharose), sugar alcohols (mannitol, sorbitol, glycerol), polyamines, amino acids (proline), betaines (glycinebetain) Membrane protection, source of C or N, defence against reactive oxygen species (ROS) Dehydrines – ripenning of seeds or pollen grains, in plant vegetative parts during stresses, induced also by abscisic acid (ABA) Elastic adjustment – expansin, endoglucanase, transglycosylase, peroxidase

Changes in water potential and its components during water stress

Water and growth Elongation: dV/Vdt  m(  p - Y) m - cell wall extensibility,  p - pressure potential,Y - threshold pressure potential dV/Vdt  L p (  w o -  w ) L p - hydraulic conductance,  w o - water potential of water source,  w - water potential of elongating cell Lockart equation: dV/Vdt = mLp/(m + Lp)  (  w +  p - Y)

Model of cell wall and possible changes of its extensibility

Aktivity of xyloglucan endotransglycosylase

Comparison of shoot and root growth rate as affected by water potential of substrate

Water stress and growth Elongation rate (a) and pressure potential (b) in different distance from root apex in two substrates of different water potential