Water-deficit accumulates sugars by starch degradation-not by de novo synthesis-in white clover leaves (Trifolium repens)

Labeling (CO2)-C-13 in steady-state condition was used to estimate quantitative mobilization of recently fixed carbon or stored sugar during water-deficit in white clover (Trifolium repens L.). Water-deficient gradually decreased leaf-water parameters and total amount of recently fixed carbon. Amount of C-13 incorporated into glucose, sucrose and soluble sugars fraction rapidly decreased after 3 days of water-deficit treatment. In contrast, the previously stored soluble sugars significantly increased after 5 days of water-deficit with a coincidence of significant decrease in starch concentration. A highly significant (P <= 0.001) relationship between the decrease in leaf-water potential caused by water-deficit and the increase in ratio of soluble sugar/starch concentration was observed in water deficit-stressed plants. The data indicate that soluble carbohydrate accumulated by water-deficit treatment is mainly because of the hydrolysis of previously stored starch rather than to de novo synthesis.