GAS EXCHANGES IN VITIS-VINIFERA UNDER WAT ER-STRESS REGIME .3. ABSCISIC-ACID AND VARIETAL BEHAVIOR

The effect of water stress on the regulation of gas exchange and on th e accumulation of abscisic acid (ABA) in the leaves of different culti vars of Vitis vinifera L. has been analysed with the purposes of chara cterizing the varietal behavior and of identifying a marker for the di fferent forms of response. Two-year old plants grafted on 'Fercal', pl anted in plastic pots and cultivated under controlled conditions were used. Long period of water stress (20 days) revealed two groups of cul tivars with different sensitivities at the gas exchange level. The ABA content of the leaves was related to the functioning of the stomata, showing that the most sensitive cultivars presented the lowest content s of ABA in the test plants, whereas the greatest accumulations of thi s hormone occurred in the stressed plants.