L. Vanrensburg et Ghj. Kruger, OSMOREGULATION, MONITORED BY PRESSURE-VOLUME TISSUE WATER COMPONENT ANALYSIS, IN CULTIVARS OF NICOTIANA-TABACUM-L OF DIFFERENT DROUGHT TOLERANCE, South African journal of botany, 60(3), 1994, pp. 139-144
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.