Mechanisms involved in diurnal changes of osmotic potential in grapevines under drought conditions

The aim of this study was the quantitative determination of the contributio n of various possible mechanisms involved in diurnal changes of osmotic pot ential in grapevine leaves (Vitis vinifera L., cv. Victoria) under water st ress conditions. Results of this study revealed that dehydration accounted for 36 % of the diurnal changes in osmotic potential in stressed plants. Th e relative contribution of changes in non-osmotic volume was negative. Net solute accumulation accounted for 73 % of the diurnal changes, indicating t he occurrence of an active osmotic adjustment during the day in stressed pl ants. There was evidence that compounds other than sugars contributed to di urnal osmotic adjustment in stressed grapevines.