الفهرس 
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Abstract
This study aimed at determining the role of aquaporins in the anisohydric behavior of sunflower. After investigation of stomatal behavior of sunflower plants grown under different growth conditions and the role of aquaporins in this behavior, we found that Sunflower leaves behaved in anisohydric manner under control conditions but choose to change this behavior under stress conditions. Different behavior of the plants was observed for different types of ions applied to induce salt stress as; NaCl-treated leaves showed near isohydric behavior meanwhile the KCl treatment resulted in anisohydry. This could be explained by the involvement of K+ ion in enhancing stomatal opening. We can evaluated the contribution of AQPs to iso/anisohydry shift on the basis of the conductance of CO2 in the leaves or increasing the water permeability in leaves and roots; the increased expression of PIP1s may have a main role in the anisohydric behavior of sunflower by improving the stomatal conductance through affecting the CO2 circulation, resulted in increased A at midday. Meanwhile PIP2s which have high water transport activity compared to PIP1s showed decreased expression in the control leaves at 13:00 compared to 9:00 to lower the water loss through transpiration due to low Ψl. But this expression was increased in the roots, indicating its turn in the anisohydric behavior as the high expression in the roots would improve the hydraulic conductivity and hence the predictable water supply to the leaf, enhancing high A and gs. The changed expression pattern of PIP1s in the leaves of the droughted leaves and of PIP2s in the droughted roots at the same time contributed in the shifting from the anisohydric to the near isohydric behavior. It seems that PIP1s and PIP2s work in a harmony to control the iso/anisohydric behavior of H. annuus.