APPLICABILITY OF ABSCISIC-ACID AND (OR) PROLINE ACCUMULATION AS SELECTION CRITERIA FOR DROUGHT TOLERANCE IN NICOTIANA-TABACUM

The efficacy of various aspects of abscisic acid and proline accumulat ion as potential selection parameters for drought tolerance in tobacco was evaluated under controlled conditions. The results indicated that both abscisic acid (though being less pronounced) and proline accumul ate rapidly after a distinct threshold leaf water potential value has been reached and that probably because of their higher cell wall elast icity (0.23 and 0.28 MPa for the drought-tolerant cultivars GS46 and E lsoma, respectively, compared with 0.39 and 0.31 MPa for the drought-s ensitive cultivars TL33 and CDL28, respectively) these threshold leaf water potential values are reached sooner in drought-tolerant cultivar s. However, abscisic acid accumulation precedes proline accumulation i n both the drought-tolerant and drought-sensitive cultivars. Proline c oncentrations increased sharply at a leaf water potential of ca. -1.27 MPa in the drought-tolerant cultivars and at a leaf water potential o f ca. -1.50 MPa in the drought-sensitive cultivars. At a leaf water po tential of -0.77 MPa the abscisic acid concentrations of all four cult ivars were already significantly higher than those of their respective controls and were greater in the drought-tolerant cultivars. The leaf water potential value at which abscisic acid and proline start accumu lating rapidly and the accumulated proline end concentrations are reco mmended as selection parameters for drought tolerance in tobacco.