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Changes in gas exchange and internal CO2 conecentration (Ci) of leaves of different ages under different water stress conditions and at different growth stages were investigated. As water stress progressed, net photosynth_is rate (Pn) and stomatal conductance (gs) declined, becoming significantly lower than those of control at per-wilting and showed a further reduction to per-wilting followed by a marked invreased at wilting stage and then a sharp decline upon rewatering. When rewatering delayed until severe
wilting, neither Pn nor gs recovered and Ci remained at a significantly higher
level than that of the control. Although chlorophyll content of wilting leaves
was not reduced, a significant reduction in chlorophyll content of leaves recovered from wilting was observed. Long term water stress, however caused a significant reduction in chlorophyll content. Ultrastructural studies revealed some alteration in the chloroplast of wilted leaves. It was concluded that mild
water stress reduced Pn mainly through reversible stomatal limitations, but under more severe or prolonged water stress conditions, non stomatal factors