Comparison Of Sucrose Metabolism In Different Cadmium-sensitive Maize Seedlings Under Cadmium Stress

As an important grain and feed crop in China,corn suffers different degrees of Cd pollution in many planting areas,which not only reduces its yield and quality,but also seriously restricts the development of the corn industry.However,the growth of maize is affected by the concentration,period and environmental conditions of cadmium stress,and there are differences among varieties.Different varieties have different tolerance to cadmium toxicity.Sugar accumulation has been shown to be one of the defense mechanisms obtained by plants in response to stress conditions to maintain the osmotic balance of plant metabolic activity.Therefore,understanding the molecular mechanisms underlying cadmium stress to regulate sugar biosynthesis or degradation,transport and distribution is critical for creating platforms to optimize whole plant carbohydrate allocation to increase productivity under stress.In this experiment,different cadmium-sensitive maize varieties were used as materials to determine the photosynthetic characteristics,dry matter accumulation,sucrose content,metabolic and transport key enzyme activities and gene expression of maize seedlings under cadmium stress.The differences of cadmium sensitivity among different maize varieties were analyzed,and the effects of cadmium stress on sucrose metabolism and translocation in maize seedling stage were analyzed.The results are as follows:(1)After cadmium treatment,the cadmium content in the roots of the two varieties of maize seedlings was significantly higher than that in the aerial part,and the accumulation of cadmium in Fuyou9 was higher than that in Shenyu33,and the leaf was lower than Shenyu33.(2)After cadmium treatment,root biomass,root growth,root tip number,average root diameter,root volume,root surface area and total root length of Shenyu33 were significantly inhibited,while the above traits of Fuyou9 were slightly inhibited and decreased.The magnitude is small.In the leaves,the net photosynthetic rate,transpiration rate and stomatal conductance of Shenyu33 were also significantly inhibited after cadmium treatment,and the chlorophyll content was significantly reduced,while Fuyou9 was less inhibited and the chlorophyll content decreased slightly.The net photosynthetic rate of Fuyou9 was higher than that of Shenyu33 under the same concentration of cadmium.The synthesis of more assimilates was beneficial to maintain its normal growth under cadmium stress.The net photosynthetic rate of Shenyu33 was greatly reduced.Growth is significantly inhibited.(3)After cadmium treatment,the contents of glucose,fructose and total soluble sugar in Shenyu33 and Fuyou9 increased,and the change of sucrose content showed a slight increase,but the changes were not significant.The content of soluble sugar in Shenyu33 was higher than that in Fuyou9 when treated with 5mg·L-1 cadmium.It is speculated that Shenyu33 is sensitive to cadmium stress,and needs more osmotic adjustment substances to maintain its own growth and development,and the treatment concentration is gradually increased.Fuyou9 has higher soluble sugar content than Shenyu33.It is speculated that when low concentration cadmium treatment,Fuyou9 has less influence on sugar metabolism,while low concentration cadmium treatment will lead to rapid change of sugar metabolism in Shenyu33,while high concentration Treatment can lead to disorders in its glucose metabolism.(4)After cadmium treatment,the activities of sucrose-synthesis-related enzymes(sucrose synthase and sucrose phosphate synthase)decreased in Shenyu33 and Fuyou9 leaves,and the enzymes involved in sucrose decomposition mainly increased acid invertase activity,which was beneficial to promote the conversion of sucrose to fructose and glucose of small molecular substances increases the soluble sugar content of plants and enhances their osmotic adjustment ability.In Fuyou9,low-concentration cadmium treatment has no significant effect on sucrose synthesis and decomposing enzyme activity,and acidity at high concentration.The activity of invertase is increased,the activity of synthetase is decreased,the rate of sucrose synthesis is slowed down,and the rate of decomposition is accelerated,which is beneficial to the accumulation of permeate.Shenyu33 is sensitive to cadmium.The treatment of cadmium at low and medium concentrations will affect its sugar metabolism,increase its sucrose-degrading enzyme activity,decrease the activity of synthetase,increase the soluble sugar content,maintain its osmotic adjustment ability,and treat cadmium with high concentration.It will inhibit the enzyme activity,leading to a decrease in soluble sugar content,resulting in disorder of glucose metabolism.(5)After cadmium treatment,the expression level of Zm SWEET13 b gene in Fuyou9 and Shenyu33 leaves first and then increased,while the Zm SWEET13 a gene and Zm SWEET13 c gene in Fuyou9 showed a downward trend,while in Shenyu33,the up-regulation trend,two varieties the expression levels of transporter genes Zm SUT1 and Zm SUT4 in roots and leaves were up-regulated,and the up-regulation of Shenyu33 was higher than that of Fuyou9.It was speculated that the activity of Shenyu33 acid invertase was inhibited after high-concentration cadmium treatment,the sucrose decompositionability was reduced,and transport was blocked.It causes sucrose accumulation and promotes up-regulation of transporter gene expression for rapid transport of sucrose.In summary,the effects of cadmium stress on sucrose metabolism and transport in different maize seedlings were different,and the degree of influence was closely related to cadmium treatment concentration.Fuyou9 had a slight decrease in photosynthesis,sucrose-degrading enzyme activity increased slightly,sucrose transporter gene was up-regulated,soluble sugar accumulation was not obvious,but glucose and fructose content increased with increasing cadmium concentration.The content of soluble sugar is also increased,and osmotic adjustment is initiated to maintain its normal growth and development.The photosynthetic rate of Shenyu33 decreased significantly,and the assimilation rate decreased,but the activity of sucrose decomposing enzyme increased,so that soluble sugar such as glucose and fructose accumulated rapidly,and the osmotic adjustment ability increased,maintaining its normal growth and development,but with the concentration of cadmium.The increase of osmotic adjustment substances such as glucose and fructose is not enough to resist cadmium stress,resulting in severe inhibition of growth and development,and significant decline in biomass.