Effect of water restriction on carbohydrate metabolism and photosynthesis in mature maize leaves

The time course of the modifications induced by a mild water stress has been examined for photosynthesis and several traits of carbohydrate metabolism in adult leaves of two inbred maize lines of North American and European origins, respectively, An early response was a sharp increase of the acid soluble invertase activity in adult leaves, 3-4 d after initiation of water shortage, Accordingly, correlated accumulations of fructose, glucose and to a lesser extent sucrose were observed, In the most responsive genotype, invertase activity finally reached a value > 3 times larger than the control value, By contrast, sucrose phosphate synthase activity, measured either under saturating or limiting substrate conditions, was progressively reduced by 20-40% on the 5th day and by 50-80% on the 7th day, depending on the genotype. Leaf photosynthetic rate was affected at approximately the same time as carbohydrate metabolism and stomatal conductance, Leaf water status, as measured by relative water content, declined afterwards, For all the observed responses, the two genotypes behaved very differently.