New Insights into Desiccation-Associated Gene Regulation by Lilium longiflorum ASR during Pollen Maturation and in Transgenic Arabidopsis - International Review of Cell and Molecular Biology - page 53

examination of stomatal opening of 35S::LLA23 leaves showed that
approximately 86% (78/91) of 35S::LLA23E stomata remained open under
drought stresses for 12 days, a percentage close to 96% (74/77) of the wild-
type stomata without stress (Fig. 2 . 3 F). The unexpected observation of sto-
matal opening was further checked by measuring the levels of ABA of both
plant types. Correlated with the opening of 35S::LLA23 stomata, the trans-
genic plants did not appreciably increase their ABA levels upon drought
stresses for 12 d, similar to that of the wild-type plants at normal growth
conditions ( Yang et al., 2005 ). It clearly indicated that due to the pres-
ence of LLA23 proteins, the response to ABA was delayed in the transgenic
plants upon water deficit. The LLA23 protein functions as a water-retaining
molecule that confers drought resistance on 35S::LLA23 plants based on
the drought test of transgenic lines, in which leaves of these plants overex-
pressing LLA23 protein had lower rates of water loss than wild-type plants
(Fig. 2 . 3 E), while 35S::LLA23 stomata remained open upon drought
stresses for 12 days. Nevertheless, if these plants were continued to withhold
water for additional 4 days, most 35S::LLA23 stomata (87%) became closed
(Fig. 2 . 3 F); transgenic plants began to wilt and their ABA levels in leaves
markedly increased.
The transpiration rate of transgenic plants was also examined. As
shown in Fig. 2 . 4 A, 35S::LLA23 leaves showed pattern of transpiration
rate similar to the wild-type leaves upon drought stress despite that 91%
(91/100) of 35S::LLA23E stomata remained open, which is opposite to
83% (88/106) of the closed stomata observed in the wild-type leaves (Fig.
2 . 4 B). It is rational that ABA in the wild-type leaves was apparently pro-
duced and let most stomata (88/106) become closed upon drought stress
while under the same drought condition, ABA in the transgenic plants did
not change, similar to the unstressed wild-type plants and thus most sto-
mata (91/100) remained disclosed. The fact that LLA23-overexpressing
plants kept approximately the same transpiration rate as the wild-type plants
while their stomata mostly remained open strongly suggests the function
of LLA23 as a water-retaining molecule in the 35S::LLA23 leaves. It cor-
relates with the results obtained when the rate of water loss from detached
leaves of wild-type and LLA23-overexpressing plants was compared (Fig.
2 . 3 E). The gin1-3 mutant, however, displayed a much more pronounced
transpiration rate because the mutant was unable to produce ABA to which
stomata respond and thus, 96% (78/82) of gin1-3 stomata remained open
(Fig. 2 . 4 B). In addition to acting as a water-retaining molecule, the LLA23
protein may protect other macromolecules from losing their biological