Gene Mapping And Functional Analysis Of Lps1 Of Rice Leaf Tip Premature Senescence Mutant

Rice leaf color mutants have important scientific significance for basic research and breeding.This study used the natural mutant lps1 produced in the rice variety Shennong 265as material.The field of mutant lps1 showed premature leaf senescence at the tillering stage,which mainly showed yellowing of the tip,and inherited the chlorophyll metabolism related gene of the mutant lps1.Analysis and functional analysis.The main results are as follows:?1?A natural mutant?lps1?with premature senescence at the tip was found in the japonica rice Shennong 265 population.A field survey found that during the tillering period of the mutant,the leaves showed senescence,which was mainly due to the premature yellowing of the tip.Compared with wild type Shennong 265,the height andseed setting rate of mutant lps1 were significantly reduced.Through the determination of photosynthetic and fluorescence parameters and chlorophyll content,the mutant lps1 had chlorophyll a,chlorophyll b,carotenoids,net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration,transpiration rate,initial fluorescence,and maxim-um at the tillering stage.The fluorescence efficiency,photochemical transfer efficiency,and light energy conversion efficiency are both significantly reduced.The ultrastructuralobservation revealed that the number of thylakoids in the mutant lps1 was reduced,the basal granules and lamellae were degenerately arranged and loosened,and the spacebetween the plasmodium and the plasma membrane increased,and the chloroplastshape changed from elliptical to slender.It was shown that the chloroplast growth in the mutant lps1 was affected.Genetic analysis showed that the tip premature bud mutant lps1 was controlled by a pair of recessive genes,and the LPS1 gene controlling the trait was located on chromosome 10 of rice by means of map-based cloning techniques,limited to MM2382 and MM2388.The physical distance between them is approximately 128kb.?2?Studies on the chlorophyll content?SPAD?value and photosynthetic fluorescence parameters of the mutant plant lps1 and the wild type plant Shennong 265 showed that the chlorophyll content?SPAD value?and Fo in the leaf tip senescence mutant lps1 Maximum fluorescence,Fm maximum fluorescence efficiency,Fv/Fm light energy capture efficiency,Fv'/Fm'maximum light and efficiency,PSII photochemical transfer effic-iency,NPQ photochemical transfer efficiency,qN light energy conversion efficiency,ETR ratio and wild type plant Shennong The result of the 265 measurement was significantly reduced.The results of these assays indicate that significant degradation of chlorophyll in the cells of the premature leaf tip mutant lps1 is associated with a sudden decrease in the photosynthetic rate of the mutant.In addition,the measurement of fluorescence parameters showed that the decrease of net photosynthetic capacity in the mutant plant lps1 was closely related to the photosystem II and structural destruction of the light-harvesting pigments,and the light-to-chemical energy conversion efficiency and net photosynthetic capacity were also observed.The decrease suggested that the accumulation of reactive oxygen species in the mutant lps1 cells may affect the photosynthesis of the mutant lps1 plants,resulting in decreased photosynthetic capacity.?3?The physiological index of active oxygen metabolism of the tip premature senescence mutant lps1 was tested.The results showed that the activity of superoxide dismutase?SOD?in the cells of the mutant plant lps1 was compared with that of the wild type plant Shennong 265.The activities of POD,malondialdehyde?MDA?,hydrogen peroxide?H₂O₂?,superoxide anion?O₂.^-?and catalase?CAT?activity were all increased.We speculated that due to accumulation of a large amount of ROS?reactive oxygen species?in the leaf cells of the mutant lps1,the activity of superoxide dismutase was increased,and superoxide dismutase catalyzed the disproportionation reaction of oxygen anions to generate hydrogen peroxide and oxygen.The large amount of hydrogen peroxide produced will lead to an increase in the activity of peroxidase in the cells.The large accumulation of reactive oxygen species in plants causes many adverse consequences,including the over-oxidation of lipid molecules in the biofilm system of cells,damage to the structure of biofilms,and the peroxidation of membrane lipids leading to malondialdehyde in cells.The accumulation of these is a series of chain reactions.Electrical conductivity is an extravasation substance,which indicates the permeability of the cell membrane,while malondialdehyde is a superoxide injury that leads to rupture of the cell membrane and leakage of cell membrane substances to increase the electrical conductivity.There is a positive correlation between malondialdehyde and electrical conductivity.Superoxide anion and hydrogen peroxide produce superoxide,and excessive accumulation of reactive oxygen species generates oxidative substances,which leads to increase of cell membrane superoxide,rupture of cell membrane and collapse of thylakoids.The superoxide dismutase decomposes the superoxide anion,generates O₂ and H₂O₂,and then generates H₂O and O₂ in the presence of catalase and peroxidase.