NaCl-Induced Changes of Ion Fluxes in Roots of Transgenic Bacillus thuringiensis (Bt) Cotton (Gossypium hirsutum L.)

Bacillus thuringiensis (Bt) cotton is grown worldwide, including in saline soils, but the effect of salinity on ion fluxes of Bt cotton remains unknown. Responses of two transgenic Bt cotton genotypes (SGK321 and 29317) and their corresponding receptors, Shiyuan 321 (SY321) and Jihe 321 (J321), to 150 mmol L-1 NaCl stress were studied in a growth chamber. The root dry weight of SGK321 and 29317 under NaCl treatment was decreased by 30 and 31%, respectively. However, their corresponding receptor cultivars SY321 and J321 were less affected (19 and 24%, respectively). The root length and surface area of the Bt cultivars were significantly decreased relative to their receptors under salt stress. NaCl treatment significantly increased Cry1Ac mRNA transcript levels in SGK321 and 29317 but did not affect Bt protein content in leaves or roots of either cultivar at 1 and 7 d after NaCl 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. There were no significant differences in Na+ efflux between Bt and non-Bt cottons. Furthermore, the Na+ contents in roots and leaves of all genotypes dramatically increased under salt stress, whereas K+ contents decreased. Our results suggested that Bt cotton cultivars are more sensitive to salt stress than their receptor genotypes.