Study On The Physiological And Biochemical Traits Of High Temperature Stress Tolerance In Cotton

A comparative investigation on the physiological and biochemical characteristics and their fluctuation in main stem leaf and pollen of cotton lines with different tolerance to high temperature stress and the influence of high temperature stress was presented in the paper. The results were as follows:1. The light response curve of three cotton was compared and analyzed at squaring stage, peak flowering stage, and boll-setting stage, the result showed the trend of peak value and Pn were HLY>XYM68>TS18. No significant difference was found in AQY (apparent photosynthetic quantum efficiency) between XYM68 and TS18 at squaring stage and boll-setting stage, but the AQY of XYM68 was higher than TS18 at peak flowering stage, and HLY was the highest among the three cotton lines at all developmental stages. The trend of LCP (light compensation point) was TS18>XYM68>HLY, and the LSP(light saturation points)of HLY was higher than TS18, and no different with XYM68 at all developmental stages.2. The leaf cell membrane thermo-stability (CMT) increased with cotton plant growth and development. The CMT was significantly stronger in tolerant line HLY than susceptible line TS18 during the whole growth period and moderately susceptible line XYM68 at peak flowering and boll-setting stages. Of the three differentially tolerant lines, the proline content was different significantly with each other at all stages except for seedling, the soluble sugar content was almost the same at seedling and peak squaring stages and became significant difference at peak flowering and boll-setting stage, while there was nearly no change for dissolvable protein content during the whole developmental period. The chlorophyll content was higher in tolerant line than susceptible counterparts at peak flowering and boll-setting stages, but not at seedling and peak squaring stages. The tolerant line HLY owned the highest net photosynthetic rate at the all four stages comparing with XYM68 and TS18. The tolerant cotton line may be distinguished from susceptible ones by the CMT, proline, soluble sugar content and net photosynthetic rate traits in main stem leaf, which can be used a measure of high temperature tolerance in cotton breeding program.3. The protective enzyme activities in main-stem leaves were nearly same among the three cotton lines at seedling and peak squaring stages, but significantly higher in tolerant line than susceptible ones at peak flowering and boll-setting stages. The MDA content was markedly lower in tolerant line than susceptible ones from peak squaring stage. Activities of protective enzymes in cotton anther were increased with developmental processing, and remarkably higher SOD and POD activities in anther at pollen maturing stage were measured in tolerant line. During the whole developmental period of anther, CAT activity was greater, while the MDA content was lower distinctly in tolerant line than susceptible ones.4. The protective enzyme activities were inhibited, and the MDA content was increased excessively in main-stem leaves and anther of the three cotton lines under high temperature stress at peak flowering stage. However, changes of decreasing in activities of protective enzymes and increasing in MDA content in leaves and anther were less obviously in tolerant line than susceptible ones. All indexes of photo-physiological characteristics, except for Ci (intercellular CO2 concentration), were influenced by high-temperature stress. Tr (transpiration ratio), Gs stomatal conductivity) decreased, WUE (water use efficiency) increased remarkably and were different significantly among the three cotton lines, but Pn (Net photosynthesis rate) and Ls (Stomata Limitation) of HLY did not change under high-temperature stress, while XYM68 and TS18 decreased remarkably, Pn and WUE of HLY were higher and Tr was lower than XYM68 and TS18, and no significant difference were found in Gs and Ls among them.