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Plant water regime

Plant water regime. Stomatal conductance Effects of environmental factors Diurnal changes Interactions among factors A cc limation Adaxial and abaxial epidermis Ontogeny Mathematic al modelling Opening and closing rate Important characteristics of guard cells.

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Plant water regime

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  1. Plant water regime • Stomatal conductance • 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

  2. 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

  3. Sengbush 2006 podle Raschke 1975

  4. 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

  5. Simultaneous effects of different factors

  6. Diurnal changes in stomatal and cuticular transpiration as affected by water stress development

  7. Response of stomatal conductance to air humidity in different plant species

  8. Effect of irradiance and internal CO2 concentration on stomatal conductance

  9. Effect of leaf water potential and irradiance on stomatal conductance of adaxial and abaxial epidermes

  10. Effect of water potential on adaxial and abaxial stomatal conductance in leaves of different age of plants grown under two different irradiances

  11. Effect of irradiance on adaxial and abaxial stomatal conductance in leaves of different age

  12. Effect of elevated CO2 concentration during plant growth on response of stomatal conductance to different factors

  13. Effect of water potential on stomatal conductance and hydraulic conductance in Ceratonia siliqua leaves(Lo Gullo et al. 2003)

  14. The dependence of stomatal conductance on water potential and irradiance

  15. The dependence of stomatal conductance on water potential and irradiance

  16. 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

  17. Light-induced stomatal opening as affected by plant age and water stress

  18. Stomatal closing induced by ABA • Influence of pH on stomatal closing induced by ABA on isolated epidermis fromCommelina 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)

  19. 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 • lower chlorophyll content • lower Rubisco activity • higher PEPC a ATPase activity • more mitochondria • photosynthetic efficiency of PS 2 70 - 80 %

  20. Different number and localization of chloroplasts in guard cells of different plant species (Lawson et al. 2003)

  21. 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 thicknessare 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

  22. Arrangement of actin filaments and microtubules under irradiance or in the dark

  23. Arrangement of microtubules

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