Photosynthesis, carbohydrate levels and chlorophyll fluorescence-estimatedintercellular CO2 in water-stressed Casuarina equisetifolia Forst. & Forst.

The effect of long-term water stress on photosynthetic carbon metabolism in Casuarina equisetifolia Forst, & Forst, was analysed by measuring CO2 assi milation, stomatal conductance, the quantum yield of photosystem II (Phi(PS II)), enzyme activities, and the levels of photosynthetic intermediates and carbohydrates, CO2 assimilation decreased under water stress while the int ercellular CO2 concentration (C-i) as estimated by gas exchange measurement s remained high, However, the estimates of C-i from measurements of Phi(PSI I) suggest that the decrease in photosynthesis can be explained in terms of stomatal closure. Water stress decreased total stromal fructose-1,6-bispho sphatase activity and did not alter the activities and activation states of ribulose bisphosphate carboxylase oxygenase and NADP-dependent malate dehy drogenase (NADP-MDH), The concentration of photosynthetic metabolites, gluc ose, fructose and sucrose decreased, whereas starch concentrations increase d under drought conditions.