OSMOREGULATION, MONITORED BY PRESSURE-VOLUME TISSUE WATER COMPONENT ANALYSIS, IN CULTIVARS OF NICOTIANA-TABACUM-L OF DIFFERENT DROUGHT TOLERANCE

The extent of osmoregulation was determined by means of pressure-volum e tissue analysis, which was also used to determine tissue water compo nents and to estimate relative water content (RWC), of the leaves of f our Nicotiana tabacum L. cultivars of different but known drought tole rance. Data were obtained during two drough stress periods induced in computer-controlled growth rooms. The tobacco leaves adjusted largely to drought stress by the accumulation of solutes, leading to a decreas e of ca. 3% (TL33), 6% (CDL28), 12% (GS46) and 16% (ELSOMA) in the osm otic potential at full turgor (psi(pi)100), which was statistically mo re pronounced (p < 0.01) in the drought-tolerant cultivars (GS46 and E LSOMA). Drought stress induced an increase in the proportion of bound water (B) and the volumetric bulk modulus of elasticity (epsilon), mor e so in the drought-tolerant cultivars, but did not alter the relative water content at which incipient plasmolysis (RWC0) was reached. In s pite of the stability of RWC0 in all four tobacco cultivars, which was ca. 79, 76, 73 and 70% for TL33, CDL28, GS46 and ELSOMA, respectively , the lower - of the drought-sensitive cultivars (TL33 and CDL28) whic h occurred during both drought stress periods, caused the leaf water p otential (psi(L)) at which incipient plasmolysis (psi(L)0) occurred, t o be consistently less negative in these cultivars. Firstly, the resul ts presented corroborate the existence of differential degrees of osmo regulation in the four tobacco cultivars, which may be part of an inte grated plant response. Secondly, they emphasize the drought tolerance adaptive advantage of being characterized by a high epsilon, and third ly, seem to indicate that since both the latter parameters may be gene tically determined, it may be used in drought tolerance selection prog rammes.