Study On Screening And Physiological Mechanism Of Low-Potassium Tolerant Genotypes From Rice Offsprings Introduced DNA Of Phytolaoca Esculenta Van Houtt

Rice(Oryza Sativa L.) is one of the most important food crops in China.K deficiency greatly influences rice yield and quality.However,K resources are very shortage in China.It is one way to solve this problem to screen low-K tolerant rice genotypes.DNA from K-rich plants Phytolaoca esculenta Van Houtt were introduced into rice variety,Jing 85-5.From their offspring 30 plants were chosen as experimental materials for screening low-K tolerant rice genotypes at seedling stages by solution culture.Meanwhile,two typical low-K tolerant rice genotypes and their recipient were carried out in solution culture to study their nutritional characters and physiological mechanism for low-K tolerance.Two levels of K supply(K0: 3mg·L^-1,K1:40mg·L^-1) were set up.Based on the studies,we expected to lay some theoretical foundations for the improvements of K efficiency and provide materials for such studies.The main results of this study were summarized as follows:1.Appropriate K concentration and effective indicators for seedling screening low-K tolerant rice genotypes were proposed.There was positive correlation between K⁺ influx rate and H⁺ efflux rate of different rice genotypes at 3-leaves stage under low K level.K⁺ influx rate and H⁺ efflux rate of low-K tolerant rice genotypes are higher than those of their recipient.The low-K tolerant rice genotypes were further screening identified by measuring their height,dry weight of shoots and roots of the 30 rice genotype plants at tillering stage under normal and low K levels.2.Fractionated,stepped selection and identification,two low-K tolerant rice genotypes N18 and N19,and their recipient N27(control) had been carried out in solution culture to study their physiological mechanism for low-K tolerance. â‘ Under low potassium stress,the height,fresh and dry weight of shoots of the recipient depressed greater than that of low-K tolerant rice genotypes,especially fresh and dry weight of shoots.Under low potassium stress,root length,root dry weight,root volume and root vigor of all genotypes were decreased,which were higher significantly of N18 and N19 than those in N27 respectively.Furthemore,low potassium stress increased the ratio of root/shoot,but the differences in it were inconspicuous among the three genotypes tested.â‘¡Under low potassium stress,the potassium uptake efficiency,potassium utilization efficiency and potassium translocation rate of all genotypes were decreased,reductions of which were less in N18 and N19 than in N27.Furthermore,under low potassium stress,N18 and N19 had stronger absorption ability and translocation ability of Na,P,Mg,Fe and Ca compared with N27.The results indicated that the characteristic of rice resistance is related to their ability to absorb mineral nutrients.â‘¢Under low potassium stress,contents of IAA,GA₁ and ZR in leaves and roots of all genotypes were decreased,reductions of which were less in N18 and N19 than in N27.Under low potassium stress,contents of IAA,GA₁ and ZR and the ratios of IAA/ABA,ZR/ABA and GA₁/ABA were higher in N18 and N19 than in N27,the increases of ABA contents were less in N18 and N19 than in N27.The results indicated that the characteristic of rice resistance is related to the content of phytohormones and their ratios in them.â‘£Under low potassium stress,contents of chlorophyll a,chlorophyll b and chlorophyll (a+b) in leaves of all genotypes were decreased,contents of them were higher in N18 and N19 than in N27.Under low potassium stress,the net photosynthetic rate,respiration rate, stomatic conductance,intercellular CO₂ concentration and transpiration rate of leaves of all genotypes were decreased,reductions of which were less in N18 and N19 than in N27.⑤Under low potassium stress,free amino acid contents and soluble suger content in leaves of all genotypes were increased,the increases of which were less in N18 and N19 than in N27.Under low potassium stress,soluble protein contents in leaves were decreased, reductions of which were more in N27 than in N18 and N19.