Researches On The Mechanism And Regulations Underlying Cold Stress Impaired Early Indica Rice

In recent years,the global climate warming increases the temperature-light resources of rice-planted regions in the Middle-Lower Yangtze Area.This contributes to the earlier sowing of the early indiaca rice varieties,and thus resuming the cultivation of double-season rice.The vegetative growth of early indica rice was prolonged when seeds were sown earlier.However,this might result in the higher risk of encountering cold stress such as"late spring cold",which might cause damages to the growth and development of rice plants.Nowadays,the researches about technologies and theries related to earlier sowing of early indica rice has been seldom documented.Thereore,four early indica rice varieties as Zhongjiazao 17,Zhongzao 39,Ganxin 203,and Lingliangyou 211,which were largly planted in the Middle-Lower Yangtze Area,were planted under different sowing dates,in which the plant growth and development,grain yield,quality,assimilate distribution and metablism were determined.Further,two rice plants such as Zongzao 39?ZZ39?and its recombinant inbred line 82?RIL82?were used to reveal mechanism underlying cold tolernce between these two rice seedling plants.According to these above results,the effect of several chemicals on the cold tolerance of rice seedling plants were also discussed.1.The grain yields of four early indica rice varieties decreased as the the sowing date delayed with a variation range of 18.4-46.2%.This was determined by the numbers of effective panicles and grains per panicle,rather than the seed setting rate and kernel weight.The sowing dates had little effect on the rice quality except for the head rice rate?HRR?,which almost decreased along with the delay of the sowing date.It was inferred that higher assimilation transport rate?dry matter and non-structural carbohydrates?was the main factor contributing to the higher grain yield and quality of earlier sown rice,as proportions of panicle dry matter weight and non-structural carbohydrates decreased along with the delay of sowing date.However,similar results were not found in the ratio of starch to non-structural carbohydrates in grains.In view of these results,we considered higher grain yield and qualtity showed in the earlier sown rice were mainly ascribed to the enhancement in the assimilation transportation to the panicle rather than the metabolism of carbohydrates in grains.2.Two rice genotypes,Zhongzao39?ZZ39?and its recombinant inbred line 82?RIL82?were subjected to cold stress for 48 h.Under cold stress,RIL82 suffered more damages than ZZ39 plants,in which the latter had higher increases in APX activity and GSH content than the former compared with their respective controls.This indicated that GSH was mainly responsible for the different cold tolerance between these two rice plants.Interestingly,under cold stress,greater increases in contents of carbohydrate,NADH,NADPH and ATP as well as the expression levels of GSH1 and GSH2 were showed in RIL82 than ZZ39 plants.In contrast,ATPase activity in RIL82 plants was adversely inhibited by cold stress while it significantly increased in ZZ39 plants.This indicated that cold stress reduced the accumulation of GSH in RIL82 plants mainly due to the inhibition on ATP hydrolysis rather than energy deficit.We inferred that the energy status determined by ATP hydrolysis involved in regulating the cold tolerance of plants by controlling GSH synthesis.3.Proanthocyanidin can significantly improve the antioxidant capacity to alleviate the damage on rice plants caused by cold stress.Under cold stress,the contents of MDA,H₂O₂ and the relative electric conductivity?REC?of procyanidin-treated plants decreased significantly,while the content of soluble sugar and the activities of SOD,POD and CAT enzymes increased signficanlty compared with control.Under cold stress,the ATPase activity was signfianly increased by proanthocyanidin.However,the ATP content of ZZ39 decreased significantly compared with control under cold stress,while no obvious difference were showed among the treatments in RIL82.Additioanly,the PARP activity was decreased by proanthocyanidin.Thus,proanthocyanidin not only promote ATP hydrolysis to improve ATP utilization efficiency,but also inhibit PARP to reduce energy consumption and thus enhance the cold tolernce in rice seedling plants.4.The early rice variety Zhongjiazao 17 was selected in this study to investigate the effect of salicylic acid?SA?and diniconazole?S08?combination on cold tolerance of rice plants at the seedling stage under the artificial climate chamber and field conditions.The results indicated that cold stress adversely damaged the rice seedlings,but such effect could be reversed when treated with SA+S08.Under cold stress,lower decrease in Fv/Fm and Y?II?of leaves were found in the plants treated with SA+S08 than those in H₂O treatment.Accordingly,lower increase in contents of MDA and H₂O₂ were found in the former than the latter under cold stress compared with their respective controls under natural conditions.In contrast,larger increased in activities of SOD and CAT as well as soluble content was showed in plants treated with SA+S08 than those treated with H₂O.Under filed conditions,the plant height of rice seedlings treated with SA+S08 decreased slightly compared with those plants treated with H₂O.However,the dry matter weight in the former was higher than the latter,especially for plants sowing at 20 Mar,the difference was significant.Therefore,we concluded that application of SA+S08 could enhance the antioxidant capacity of rice leaves to reduce oxidant stress caused by cold stress.