After the drought stress treatment, the WT plant was markedly dehydrated and withered, while the T1
transgenic plants showed a little of dehydration but no obvious wilting. As for the NaCl treatment, the WT
was notablely etiolated and growth of plant was severely inhibited, by contraries, the Pp14-3-3 transgenic
plants did not show evident chlorotic symptom. Obviously, the Pp14-3-3-overexpressing T1 transgenic
tobacco lines showed higher level of resistance to drought and NaCl stresses than the WT.
As one of the strongest ROS among the free radicals, superoxide anion can damage biomolecules, what is
more, the MDA is formed as an end product of lipid peroxidation caused by ROS and other free radicals in
membranes. Under normal condition, the superoxide anion production rate and MDA level were not
significantly different among all the tobacco plants, nevertheless, the two physiological parameters of T1
transgenic plants were much lower than WT under drought and salt stresses. Similarly, it had reported that a
tomato 14-3-3 gene TFT7 was overexpressed in Arabidopsis, and transgenic lines showed evidently decreased
H2O2 and MDA generations (Xu and Shi, 2007). Apparently, the oxidative damage caused by drought and
NaCl was greatly decreased in the Pp14-3-3 overexpressing tobacco plants, and protection on membranes was
evidenced through the reduction of MDA level in the Pp14-3-3 transgenic tobacco lines under abiotic stresses.
During abiotic stresses, the interaction of 14-3-3 with APX is helpful in protecting plant cells from
oxidative stress (Zhang et al., 1997; Lukaszewicz et al., 2002). APXs are widely located in most of chambers
of plant cells and functions as enzymatic ROS scavenger (Smirnoff, 2005). In this study, the assay of APX
activity indicated that APX in WT and Pp14-3-3 transgenic tobacco lines did not show significant difference
during normal development. After stressed by drought and NaCl, APX activity increased in WT and
transgenic lines, but the increase amplitude in the 3 T1 transgenic lines was greatly higher than that in the
nontransgenic plant. Based on these data, there is no doubt that the overexpression of the Pp14-3-3 in tobacco
up-regulated APX activity through this mechanism to scavenge of ROS and enhance tolerance to oxidative
damage.
In this paper, the overexpression of Pp14-3-3 from P. pyrifolia fruit in tobacco plants significantly
enhanced the drought and salt tolerance. To be sure, the Pp14-3-3 gene was involved in defence response to
drought and salt stresses and could be used to develop novel drought- and salt -tolerant cultivars in the future.