Physiological Analysis And Gene Mapping Of White Stripe Leaf Mutant Ws20 In Rice

The white stripe mutant ws20?White Stripe 20?in this study was obtained by Japonica rice Shennong 9816?SN9816?by ethyl methanesulfonate?EMS?.The determination and analysis of leaf photosynthesis,chloroplast ultrastructure and important agronomic traits were carried out on mutants ws20 and wild-type SN9816,and the location of mutants' genes was also conducted.The results are as follows:1.Under field conditions,the ws20 mutant had green leaves before the 4-leaf stage,but the leaves formed afterwards were all leaves with longitudinal whitening stripes.The height of mutant ws20 was significantly shorter than that of SN9816 by 16.75%,and the leaf length of flag leaf was significantly decreased by 1.17%.There was no significant difference in tiller,indicating that the leaf color mutation had certain influence on plant height and flag leaf length,and tillering could not be affected.2.The content of chlorophyll b and total chlorophyll in the mutant ws20 were significantly reduced,as a result the light energy absorbed and captured by the flag leaves was significantly reduced,but the PSII reaction center was not significantly affected.In turn,the energy conversion efficiency of PSII reaction center is improved,and the quantum production for heat dissipation is correspondingly reduced.The decrease in photosynthetic capacity of mutant ws20 is mainly caused by a decrease in dark reaction carbon assimilation enzyme content and activity.The relative extravasation conductivity and malondialdehyde content of the mutant ws20 flag leaf increased significantly compared with SN9816,indicating that the biomass membrane of the mutant was damaged to some extent.3.Compared with the wild type,the mutant ws20 chloroplast is irregularly arranged,the starch granules are reduced,there are no larger starch granules,and the eosinophilic granules are increased.Compared with wild type,the content of ALA,PBG,Urogen III,Coprogen III,Proto IX,Mg-Proto and Pchlide in mutant ws20 was significantly decreased.ALA was the third product in the synthesis pathway of chlorophyll precursors,and its content decreased.The synthesis of the subsequent precursor materials is limited,and the corresponding content is reduced,eventually leading to a decrease in the overall chlorophyll content of the mutant ws20.4.The white stripe mutant ws20 hybridized with indica rice IR36,and F₁ showed normal leaf color.F₂ showed traits separation.Through field investigation and chi-square test,it was found that the separation ratio of normal leaf color and white striped leaf color in F₂ population was in accordance with 3:1 separation,indicating that the white streak trait of this mutant ws20 was controlled by a pair of recessive nuclear genes.5.Using the map-based cloning method,the mutant gene was mapped to 43.0 c M-70.6 c M on chromosome 6,and the ws20 white-striped gene was finally mapped to B6-7-50.3 and Chr06MM1109 by expanding the population and encrypting the primers.The physical distance between them is about 576 kb.