Effects Of Chitosan On Antioxidant System And Chloroplast Photosynthetic Function Of Hybrid Rice Leaf Under Low Temperature

The effects of chitosan on antioxidant system and chloroplast photosynthetic function of a newly-developed cultivar super-hybrid rice Liangyoupeijiu were studied under low temperature at its seedling stage and full-exhibition period. The results showed as follows:1 .The first part indicated that under low temperature, the increasing extent of the activity of SOD and GR was higher in Liangyoupeijiu than that in Shanyou63.The activity of CAT in Liangyoupeijiu increased,while that in Shanyou63 decreased. Isoenzyme of POD had evident new expression in Liangyoupeijiu, which was not obvious in Shanyou63.All the above showed that the protective enzyme system of Liangyoupeijiu was superior to that of Shanyou63. ASA and GSH cooperated with each other to clean peroxid. The increasing extent of the content of ASA and GSH were higher in Shanyou63 than in Liangyoupeijiu ,which meant the protective nonenzyme system of Liangyoupeijiu was weaker than that of Shanyou63.The producing velocity of O₂^- was lower in Liangyoupeijiu in chilling situation than the normal.But the case was opposite in Shanyou63 . The decreasing extent of chloroplast auto-fluorescence was lower in Liangyoupeijiu than that of Shanyou63. The findings indicated that the cold-resistance ability of super-high-yield hybrid rice Liangyoupeijiu was better than the traditional rice cultivar Shanyou63.But at the later period of chilling stress, O₂^- producing velocity and MDA content in Liangyoupeijiu was higher than the normal.This showed that the balance of the clean system of O₂^-had been destroyed.2.At the seedling stage, many physiological data changed obviously in low temperature .Some data decreased , such as the chlorophyll content, the activity of SOD,POD,CAT,APX,GR , the content of GSH and ASA , photosynthetic O₂ evolution and activity of Hill reaction, activity of photophorylation and ATP content, activity of Mg²⁺- ATPase and Ca²⁺- ATPase. Some data increased, such as soluble protein and proline content ,O₂^- produce rate and MDA content and the ratio of chlorophyll a/b. The treatment of chitosan alleviated the decrease of antioxidant enzymatic activities .The accumulation of O₂^- and MDA was lower in chitosan-treated samples than in chilling control, which decreased the oxidation stress damage to the membrane system and photosynthetic organs .Comparing with the chilling control, the treatment of chitosan also enhanced the activity of ATPase and the content of chlorophyll ,which maintained higher photophorylation activity and ATP content. In the four concentrations of chitosan, 0.5% was the best.3.At the full-exhibition period, the leaves of rice in low temperature were sprinkled with 0.5% concentration of chitosan . Chitosan can enhanced the activity of antioxidant enzyme and the content of antioxidant substance, which alleviated the damage of oxidation stress. So the photosynthetic organs were protected .All of this ensured the normal work of photosynthesis function.Analysis and inference: Preceding research had shown that Chitosan treatment could increase the content of unsaturated fatty acids of thylakoid membrane under low temperature, which reduced the phase transition temperature ,and maintained the fluidity and integrity of the membrane structure. Therefore, chitosan can integrate membrane-bound enzymes such as antioxidant enzymes and ATPase very well into the membrane through its protection to the membrane system, which maintained their biological activity. Thus chitosan treatment can effectively remove ROS, avoiding membrane lipid peroxidation, which could protect the membrane system further. At same time , ROS reduction can reduce its damage to chlorophyll and photosynthesis organ, which maintained the stable structure of the photosynthetic membrane system and guaranteed the normal photosynthetic functions. The increased ATPase activity ensured higher activity of photophorylation, thereby guaranteeing sufficient ATP content to meet the energy demand of the resistance in low temperature. In addition, it was suggested that Chitosan treatment could also increase the content of cellular compatible material which was beneficial to enhance cell osmotic pressure and water-holding capacity. All of this could raise the cold resistance of rice .