Effect Of Low Temperature Stress On Physiological Characteristics In Cotton(Gossypium Spp.) And Expression Analysis Of Key Enzymes Genes

In this experiment, six cotton cultivars including two precocious, two medium and two late-mature cultivars were treated with low temperature of4℃to select the strong resistance varieties in the seedling stress. The effects of low temperature treatment on physiological characteristics, cell ultrastructure and expression profiles of superoxide dismutase gene (CSD2a and CSD3) were analysed and the stress resistance of cotton seedling was compared with different cotton cultivars.The main experimental results are summarized as the followings:(1) By comprehensive evaluation on physiological index including SOD activity, POD activity, O2-content, soluble sugar content, soluble protein content, MDA content and relative conductivity after3days under the low temperature stress treatment, it was found that the comprehensive evaluation values were higher in the early-maturing varieties zhong50and N52. They were0.51and0.79respectively. It showed that the early-maturing varieties had the stronger resistance under cold stress..(2) Under the4℃low temperature treatment, the various organelles of the mid-maturing varieties N177%N188and the late-maturity varieties K-1、N2O3were seriously damaged. The chloroplasts were damaged and disintegrated seriously, mitochondrials degraded, nucleus disappeared, chromatin condensed, starch granules and osmiophilic particles increased. But the early-maturing varieties Zhong50and N52were not damaged seriously. There was nearly no change in the chloroplasts.The mitochondrials and the cell walls maintained morphological structure integrity. This showed that the cold resistance of the early-maturing varieties Zhong50and N52was stronger.(3) The expression patterns of CSD2a and CSD3at transcription level were investigated by real-time quantitative RT-PCR under4℃and NaCl stress conditions. The results showed that:there were significant differences of expression patterns between different varieties. At4℃stress, CSD2a gene expression of N52reached the highest levels. After2days under NaCl stress condition, CSD2a gene expression of Zhong50reached the highest levels. By4℃low temperature stress and NaCl stress, CSD3gene expression levels of the early-maturing varieties of Zhong50were higher, and those of N52were slightly lower than Zhong50. It indicated that the SOD enzyme activity and stress resistance of cotton seedlings was closely related. Comparative analysis showed that the stress resistance of the early-maturing varieties was stronger.