Physiological Mechanism Of Function-stability In Rice Flag Leaf During Late Growth Period

Premature of functional leaves,especially the flag leaf,can reduce the stability of leaf function,cause damage to the photosynthetic mechanism and reduce photosynthetic rate and transport rate of organics to the grain during grain-filling.Then the length of time during functional photosynthesis and grain-filling is reduced,as well as the dry matter accumulation and the development of grains,thus affecting the yield and quality of rice significantly.Flag leaves of different varieties of rice(93-11,N22,TXZ-25)show dramatic difference about the start time and the degree of senescence during grain filling in the same growing environment and cultivation conditions.In order to uncover the physiological mechanism on stability of function in rice flag leaf during late growth period,it is necessary for us to analysize the morphological characteristics,physiological properties and the expression of genes involved in antioxidant and ABA signaling pathways in the flag leave of different varieties.The aim of this research is obtaining the physiological and genetic indexes to evaluate the functional stability of rice varieties in the late growth period,which can provide reference for the physiological breeding of rice.The following main results were obtained after five years of repeated tests.1.In each variety of rice during grain filling,SPAD value,content of chlorophyll and carotenoid,net photosynthetic rate were all reduced to single direction,while MDA content,gene expression level of SODCc1,SODCc2,SODCP,CATA,CATB,CATC,SAPK8,SAPK9 and SAPK10 emonstrated relatively low or lowest value in the middle stage of grain filling.Moreover,SPAD and dry weight per pancile had significant negative correlation,the expression of SAPK8 and SAPK10 had extremely significant positive correlation.In 93-11 and N22,SPAD and Pn had extremely significant positive correlation.2.The flag leaves of ?93-11? showed a clear trend towards earlier onset and less variation of the indices during grain filling.The anti-senescence property of the three varieties was in the order ?93-11?,?TXZ-25? and ?N22?,from strong to weak.3.By RNA-seq,we received 254 pathways related to the different expression genes that can be used to research the mechanism of chloroplast development,function and the biosynthesis of chlorophyll.For example,the expression level of gene encoding EC: 5.1.3.2(UDP-glucose 4-epimerase)was down-regulated after the leaf turned to be green.UDP-glucose 4-epimerase involved in the biosynthesis of galactolipid and photosynthetic membrane.4.Function prediction and sequencing of mutant gene indicated that the mutant gene of virescent rice seeding maybe related to the biosynthesis or activity regulation of gibberellins,thus affecting the development and function of cholorplast and cholorphyll content.These results can provide some internal reference indices for the evaluation of the function stability of rice leaves from different varieties.Large number of differentially expressed genes related to the chloroplast structure stability,metabolic process and oxidation resistance can also be used to research the mechanism of function recession of rice flag leaf during late-growth period.