Molecular responses of Bt transgenic corn (Zea mays L.) plans to salt (NaCl) stress

Non-transformed and Bt transgenic crop lines of a hybrid (YieldGard 2) corn (Zea mays L.) plants in the 4th leaf stage were subjected to 0, 50, 100 and 150 mM NaCl. Significant (P = 0.05) reduction in growth of non-traformed plants was recorded under almost all levels (50, 100 and 150 mM) of salt (NaCl) stress; while, the growth of the Bt transgenic corn plants showed no significant changes under the same levels of salt stress. Chlorophyll a contents were reduced at 150 mM NaCl only; but did not change in the BT transgenic corn plants. Chlorophyll b was not responsive to NaCl treatments in both non-transformed and Bt transgenic corn plants. Chlorophyll stability index (CSI) were always higher in the Bt transgenic than in the non-transformed corn plants under all salinity levels. The analyses of SDS-PAGE revealed relative stability in the patterns of protein bands in the Bt transgenic corn plants under salinity stress. The sum of optical densities of protein bands was higher in the Bt transgenic corn plants. In response to salinity stress, a group of polypeptide (76.96, 59.38, 41.56, 33.5 and 31.26 KDa) were newly synthesized in both non-transformed and Bt transgenic plants. Salt-susceptible polypeptides of molecular weights 325.47, 32.64 and 24.17 KDa were found only in non-transformed corn plants and completely disappeared under all level of salt stress; while two polypeptides of molecular weights 38.59 and 30.61 KDa were totally inhibited in all salt-stressed corn plants. The synthesis of another four polypeptides (298.81, 99.82, 20.79 and 19.43 KDa) was solely specific to the Bt transgenic corn plants. Stability of chlorophyll pigments and molecular weights of salt stress responsive proteins are key genetic determinants of salt stress in Bt transgenic corn plants.