Download Stomatal conductance

Plant water regime
• Stomatal conductance
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Effects of environmental factors
Diurnal changes
Interactions among factors
Acclimation
Adaxial and abaxial epidermis
Ontogeny
Mathematical modelling
Opening and closing rate
Important characteristics of guard cells
Stomata and environmental conditions
• The primary role of stomata is optimalization of CO2 influx and H2O
efflux under various environmental conditions
• Environmental conditions:
• immediate effects
• acclimation
• adaptation
• Responses of stomata are dependent on plant species, age, leaf
insertion level, may be different on adaxial and abaxial epidermis or in
different parts of a leaf
Sengbush 2006 podle Raschke 1975
Stomatal opening
• Stomata: a pair of guard cells + 1-3 pairs of subsidiary cells
• Opening of stomata is dependent on:
• Pressure potential of guard cells and elasticity of their walls
• Pressure potential of subsidiary cells and of other epidermal cells
• Effects of environmental factors are direct and/or indirect
• Feedbacks
• Isohydric a anisohydric plants
Simultaneous effects of different factors
Diurnal changes in stomatal and cuticular transpiration as
affected by water stress development
Response of stomatal conductance to air humidity in different plant species
Effect of irradiance and internal CO2 concentration on stomatal
conductance
Effect of leaf water potential and irradiance on stomatal conductance of
adaxial and abaxial epidermes
Effect of water potential on adaxial and abaxial stomatal conductance in
leaves of different age of plants grown under two different irradiances
Effect of irradiance on adaxial and abaxial stomatal conductance in leaves
of different age
Effect of elevated CO2 concentration during plant growth on response of
stomatal conductance to different factors
Effect of water potential on stomatal conductance and hydraulic
conductance in Ceratonia siliqua leaves (Lo Gullo et al. 2003)
The dependence of stomatal conductance on water potential and irradiance
The dependence of stomatal conductance on water potential and irradiance
Velocity of stomatal movements
• Important for diurnal regulation of gas exchange and during sudden
changes of environmental conditions
• Closing is usually more rapid than opening
• Different in different plant species, age, growing conditions
• Advantage of high velocity is protection against water deficit
• Advantage of low velocity - CO2 influx is not decreased at variable
irradiance due to clouds or sunflecks
Light-induced stomatal opening as affected by plant age and water stress
Stomatal closing induced by ABA
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Influence of pH on stomatal closing
induced by ABA on isolated
epidermis from Commelina
communis (A) or Arabidopsis
thaliana (B). Epidermal strips
were incubated at pH 7 (open
points) or pH 5 (closed points)
under irradiance and low CO2
concentration. After complete
opening they were treated by
10 M (squares) or 10 nM
(triangles) ABA for 2 h.
(Prokic et al. 2006)
Important characteristics of guard cells
• Guards cells
• as distinct from other epidermal cells
– have not plasmodesmata,
– have chloroplasts (with exception of Paphiopedilum)
• as distinct from mesophyll cells have
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lower chlorophyll content
lower Rubisco activity
higher PEPC a ATPase activity
more mitochondria
photosynthetic efficiency of PS 2 70 - 80 %
Different number and localization of chloroplasts in guard cells of
different plant species (Lawson et al. 2003)
Guard cell structure
• low modulus of elasticity enables relatively high changes in volume at
relatively low changes in pressure potential
• radial arrangement of cellulose microfibrils in cell wall matrix and
different cell wall thickness are important for stomatal opening
• microtubules – arrangement may change during day or by ABA, they
might be important for orientation of newly synthetized cellulose
microfibrils
• actin filaments – under opening induced by irradiance or high air
humidity actin filaments are radially arranged, in the dark or after ABA
treatment irregular arrangement of short fragments can be seen
Arrangement of actin filaments and microtubules under irradiance or in
the dark
Arrangement of microtubules