Identification Of Cold Tolerance At Seedling Stage Among Main Rice Cultivars In Heilongjiang And Regulation Of Abscisic Acid

Rice (Oryza sativa L) is a warm-dependent plant, which would be damaged by low temperature at any stage of its growth. Cold tolerance at seedling stage have relationships with tolerance of other stages, because of it's significance for screening of cold-tolerance germplasm resources and studying mechanisms of cold-endurance in rice, more and more attentions are given to it nowadays. Heilongjiang province have lots of rice planting regions with high latitude, containing plenty of rice cultivars in cold region, however cold makes badly destructions there. So the study on cold tolerance of rice seedling could provide academic and experimental proof to researches of genetical breeding and cold-endurance mechanisms in rice.Study with main rice cultivars in Heilongjiang province. Firstly according to the 4 screening criteria of dead seedling rate, the rolling index, wilting degree and chlorosis degree of rice leaves, 116 cultivars was identificated to understand their cold-endurance levels at seedling stage, so both cold tolerant and cold sensitive cultivars were made out. Then difference of physical criteria such as activities of enzyme SOD, POD and contents of MDA between cold tolerant and cold sensitive cultivars were investigated in succession. Finally the different sub-cellular locations where accumulation of H2O2 occurred between those two cultivars above were contrasted, main study result was below:1. 116 cultivars of rice were clustered into three groups: cold endurable, intermediate and cold sensitive, by the criteria of dead seedling rate, the rolling index, wilting degree and chlorosis degree of rice leaves referring to Nipponbare (cold tolerant variety) and Kasalath (cold susceptive variety) from international rice research institute.2. Rice seedlings of Dongnong 418 (cold tolerant variety) and Songjing 9 (cold susceptive variety) were treated with abscisic acid (ABA) and it's biosynthesis inhibitor tungstate, then ttreated under cold meanwhile the physical criteria of cold tolerance were investigated. It was found that exogenous ABA could enhance the ability of rice seedlings to resist low temperature stress by slowing down the decrease of SOD activity and the increasing POD activity as well as the MDA content. But tungstate accelerated the decrease of SOD activity and made the POD activity and the MDA content increased. While the ABA's effects varied among different rice cultivars, it was more effective to Dongnong 418 whicn with better cold-tolerance ability.3. Histochemical location of H2O2 in rice leaves with DAB staining revealed that H2O2 in rice leaves induced by cold and exogenous ABA mainly accumulated near veins, H2O2-accumulation speed induced by ABA was faster than by cold. Combination of electron microscope technology and CeC13 coloration methods revealed H2O2's accumulative location in sub-cellular construction of rice leaves both under ABA and low temperature stress, and mainly occurred in the walls of mesopyll cells facing large intercellular spaces. But H2O2 accumulation didn't occur in organelles such as chloroplast, mitochondria, nucleolus, endoplasmic reticulum and vacuoles.