| Cotton is classified as moderately salt-resistant. Transgenic cotton expressing Bt(Bacillus thuringiensis) toxins provides highly effective control of cotton bollworm. Bt cotton is grown worldwide, often in saline soils, Extensive research has focused on the effects of salinity on both transgenic and conventional cotton cultivars. but whether and why salinity affect Bt protein production of transgenic cotton remains unknown. Our results suggest that Bt cotton cultivars are more sensitive to salt stress than non-transgenic cotton genotypes. The results are as follows:1. The effects of salt stress on transgenic cotton growth and insect resistance were studied under saline soil in the field. Bt toxic protein content of leaves in the whole developing stage were decreased with increasing salt stress, The adverse effect on salt-sensitive varieties99B and CCRI41were greater than the other three cultivars by salt stress. The yield of cotton all varieties have been severely affected under salt stress conditions, the impact of salt stress on cotton production mainly due to reduce the number of fruiting branches and bolls. The sodium content of leaves for all cultivars was dramatic increased and the potassium content of leaves for all cultivars was dramatic decreased.2. The content of Bt toxic protein in detached leaves of99B and SCRC21were significantly decreased by NaCl treatment. Condensed tannin content of both cultivars was not affected by salinity stress. However, the contents of sodium, free amino acid and the protease activity, peptidase activity in detached leaves of both cultivars were increased with increasing NaCl concentration. In contrast, the contents of potassium, soluble protein, glutamine synthetase (GS) and nitrate reductase (NR) activities in both cultivars were decreased by salt stress. Results from the present study suggested the reduction in levels of Bt protein in detached leaves could simply be part of the overall decreased levels of soluble protein in cotton caused by salt stress.3. The biomass of SGK321and29317under NaCl treatment was decreased. NaCl treatment significantly increased CrylAc mRNA transcript levels in SGK321and29317but did not affect Bt protein content in leaves or roots of either cultivar at1and7days after treatment. Fluxes of Na+, K+, and H+in roots were investigated using the scanning ion-selective electrode technique. Both mean K+efflux rate and transient K+efflux of the Bt cultivars increased four-fold compared to their corresponding receptors when exposed to salinity stress. The Na+contents in roots and leaves of all genotypes dramatically increased under salt stress, whereas K+contents decreased. Our results suggest that Bt cotton cultivars are more sensitive to salt stress than their receptor genotypes.4. Treatment with COR or MC enhanced tolerance of salt stress through increased accumulation of K and decreased the content of Na. Total N was decreased by salt stress while it was increased by COR and MC under salt stress. COR and MC also increased leaf soluble protein content under salt stressed conditions. Salinity stress decreased leaf Bt protein content of both transgenic cotton, the Bt protein content of COR and MC treated plants were44%and63%higher than NaCl-treated plants for29317. Treatment with COR or MC enhanced tolerance of salt stress through increased accumulation of chlorophyll and net photosynthetic rate. Moreover, under salt stress conditions, H2O2, MDA, and Proline levels increased sharply. COR and MC might alleviate adverse effects of salt stress of cotton by reduction of H2O2production, enhancing or keeping the net photosynthetic rate. Both COR and MC can ameliorate the adverse effects of salt stress, and enhance the ability for salt stress resistance in Bt transgenic cotton seedlings. |
PDF Full Text Request