Effects Of Salt Stress On Carbon Metabolism And Yield Formation In Rice

Rice(Oryza sativa L.)is one of the most important food crops in the world and is critical in China's food security and even world food production.Salt damage is one of the most unfavorable limiting factors in rice production,which has caused huge losses to rice production in China.Based on previous studies,this experiment uses salt-tolerant variety Longdao 5 and salt-sensitive variety Mudanjiang 30,seting five salt concentrations(Na Cl accounts for 0%,0.075%,0.15%,0.225%,0.3% of total soil weight.The treatments of Mudanjiang 30 were recorded as M1,M 2,M3,M4,and M5,respectively.The treatments of Longdao 5 were recorded as L1,L2,L3,L4,and L5,respectively.)to study the effects of salt stress on carbon metabolism and yield formation in rice.The aim is to enrich the physiological basis of rice salt tolerance research.Below are key research findings:(1)The soluble sugar content,sucrose content,sucrose synthase(SS)activity and sucrose phosphate synthase(SPS)activity of Mudanjiang 30 and Longdao 5 functional leaves showed a single-peak curve with the development of growth period.It peaked at the filling stage,and the content of soluble sugar and sucrose increased with the increase of soil salinity.Comparing the varieties,the functional leaves of Mudanjiang 30 accumulated more soluble sugar and sucrose than Longdao 5 when the soil salinity reached 0.3%.The content of soluble sugar and sucrose in stems and sheaths showed a single peak curve and peaked at the heading stage,what's more,the content increased with the increase of soil salinity.The soluble sugar output,output rate and contribution rate to grain weight of stem and sheath decreased with the increase of soil salinity.(2)The contents of soluble sugar and sucrose in grains of Mudanjiang 30 and Longdao 5 increased with the increase of soil salinity.The SS activity of grain was a single-peak curve,but when the soil salinity reached 0.15%,the peak arrival time of SS enzyme activity in Mudanjiang 30 was delayed;the change trend of SPS activity was different,the control and the lower soil salinity had a downward trend since the 7th day after the heading(M1,M2,L1,L2,L3),the other salinity treatments showed a single peak curve trend of increasing first and then decreasing.Correlation analysis showed that there was a significant positive or positive correlation between SS activity and soluble sugar content and sucrose content between 14~21 days after heading,while SPS activity was significantly positively or positively correlated with soluble sugar content and sucrose content at 28~35 days after heading.(3)The total starch content and amylopectin content of Mudanjiang 30 and Longdao 5 grain decreased with the increase of soil salinity,while the amylose content increased.The peak activity of soluble starch synthase(SSS),ADPG pyrophosphorylase(ADPGppase)and starch branching enzyme(Q enzyme)decreased under salt stress.When the salinity content of soil was 0.225%,the peak arrival time of key enzymes activity of starch synthesis in Mudanjiang 30 was delayed,while Longdao 5 was 0.3%.Correlation analysis showed that the Q enzyme activity and grain amylopectin content were significantly positively correlated at 14~35 days after the heading,and the SSS activity and amylopectin content in the grain were significantly positively correlated at 7,14 and 35 days after the heading,indicating that the grain Q enzyme and SSS complete the synthesis of amylopectin together.There was a significant positive correlation between ADPG pyrophosphorylase and total starch content at 7 and 35 days after heading,indicating that ADPG pyrophosphorylase mainly acts in the early and late stages of grain filling process.(4)The tiller number and leaf area of Mudanjiang 30 and Longdao 5 showed a single-peak curve,while the growth of plant height was from fast to smooth.And the plant height,tiller number and leaf area of Mudanjiang 30 and Longdao 5 decreased with the increase of soil salinity.Under the same soil salinity,the leaf area of Mudanjiang 30 was lower than that of Longdao 5,and the maximum number of tillers of Mudanjiang 30 was higher than that of Longdao 5;the final plant height of Mudanjiang 30 was higher than that of Longdao 5.(5)The dry matter accumulation in the aboveground part of Mudanjiang 30 and Longdao 5 decreased with the increase of soil salinity,and the decreasing amplitude was gradually increased.By comparing the decreasing amplitude in the final accumulation of dry matter in aboveground organs,it can be found that the grain is more sensitive to salt stress than the stem and leaf.When the salt content of soil was 0.3%,the allocation ratio of dry matter accumulation of leaves,stems and sheaths increased at heading stage and maturity stage,while the allocation ratio of dry matter accumulation of grains decreased.In terms of varieties,the dry matter increased in grain and the contribution rate of dry matter transport in vegetative organs of Mudanjiang 30 were lowe r than those of Longdao 5 when the salt content of soil reached 0.15%,it indicated that Longdao 5 maintained high accumulation and transfer ability under salt stress.(6)The final growth(A),maximum grouting rate(GRmax)and average grouting rate(GRmean)of Mudanjiang 30 and Longdao 5 decreased with the increase of soil salinity,while the days to reach the maximum filling rate(Tmax)and continuous grouting time(D)is prolonged.The superior grains had larger A,GRmax,GRmean and shorter Tmax and D tha n the inferior grains.Comparing the varieties,salt stress had a great influence on the inferior grains A of Longdao 5,while the superiors grain A maintained a relatively high level when the soil salt content reached 0.225%.The advantage of strong grain is enough to make up for the disadvantage of weak grain filling,finally,A is higher than Mudanjiang 30 when the soil salt content is higher.(7)With the increase of soil salinity,the number of effective panicles number,grains number,seed setting rate and 1000-grain weight of Mudanjiang 30 and Longdao 5 decreased gradually.Salt stress inhibited the grains number and seed setting rate of Mudanjiang 30 more significantly,while Longdao 5 was the effective panicles number and seed setting rate.Under the same salt stress,the decreasing amplitude of grains number,seed setting rate and 1000-grain weight of Mudanjiang 30 were higher than those of Longdao5.In addition,the yield data showed that salt stress had a significant inhibitory effect on yield.When the soil salinity reached 0.075%,the yield of Mudanjiang 30 decreased significantly,and the yield of Longdao 5 decreased significantly when the soil salinity was 0.15%.