WATER STRESS IN PLANTS .1. ABSCISIC-ACID LEVEL IN TOMATO LEAVES AFTER A LONG PERIOD OF WILTING

The abscisic acid (ABA) content was determined quantitatively in the leaves from wilted and unwilted tomato plants (Lycopersicon esculentum Mill. cv. ''Revermun'') by the use of the wheat coleoptile test and GLC. Plants which have received an insufficient daily water supply for 18 days showed adaptation to wilting conditions. The plants adjust to the added amount of water by regulating their water loss through transpiration. The concentration of ABA was not higher in the leaves of plants adapted to water stress than in plants that were watered abundantly. Wilted detached leaves and leaves from rapidly wilted intact plants showed the well-known reaction by increasing the ABA level. A possible role of ABA in the early stages of the adaptation process is discussed.