Effects Of Tryptophan Treatment On Growth And Resistance To CdCl₂ In Rape

Rape is a common vegetable plant of Brassica in Cruciferae.It is rich in nutrition,contains a lot of dietary fiber,vitamin C,vitamin B2,folic acid,?-carotene and high content of potassium,calcium and magnesium.It has the health care effect of reducing blood fat and risk of cardiovascular and cerebrovascular diseases.Tryptophan is one of the essential amino acids for protein biosynthesis.Human and animals can not synthesize tryptophan and must obtain them from plants.Therefore,tryptophan is one of the important nutritional components of plant food.Like Arabidopsis,rape belongs to Cruciferae,with the help of model plants,the metabolism network of tryptophan in Cruciferae has been studied deeply.Starting from tryptophan,the plant hormone IAA,the secondary metabolites indole glucosinolates and the phytoalexin camalexin can be synthesized respectively through the intermediate indole-3-acetaldoxime.Auxin plays an important role in the growth and development of plants,while glucosinolates and phytoalexin function in the defense of plant diseases and insect pests.Indole-3-carbinol,the main degradation product of indole glucosinolates,has been proved to have anticancer activity in recent years,which is closely related to the nutritional and health value of rape.In addition,tryptophan can also improve the resistance of plants to drought,salinity and heavy metals.To sum up,the metabolism of tryptophan in rape may play a variety of roles,not only affecting the growth and development of rape,but also closely related to the yield,resistance to biotic and non abiotic stress,nutrition and health value.Therefore,it is of great significance to carry out the research on the effect of tryptophan on the growth and development of rape.In this study,we comprehensively evaluated the positive significance of tryptophan treatment on improving the yield and resistance of rape.We detected the changes of biomass,the gene expression level in the main metabolic network downstream of tryptophan,including auxin and indole glucosinolates metabolic pathway,and the changes of resistance of rape to heavy metal Cd Cl₂.The suitable concentration of tryptophan and appropriate treatment method were optimized.Our study provides a data reference for the utilization of tryptophan to improve the yield and stress resistance of Cruciferae plants such as rape,and explores the possible mechanism of tryptophan in plant growth and development and stress defense.The main results are as follows:?1?Tryptophan treatment promoted the growth and development of rapeSpraying tryptophan with appropriate concentration?100mg/L?on the leaf surface can increase the fresh weight of aboveground part of rape seedlings and promote the development of root system.Simultaneously,spraying tryptophan with high concentration?500mg/L?on the leaf surface can also increase the fresh weight of aboveground and underground part of rape seedlings,but the effect is not as obvious as that of low concentration?100mg/L?tryptophan treatment.Low concentration of tryptophan can promote the expression of tryptophan synthesis pathway genes,thus promoting the synthesis of tryptophan,while high concentration of tryptophan has feedback inhibition on the synthesis of tryptophan.Tryptophan treatment can promote IAA synthesis by activating three IAA synthesis pathways IPA pathway,IAM pathway and IAOx pathway,so as to promote the growth of aboveground part and the development of root system.?2?Tryptophan treatment increased the content of Indole glucosinolates,a secondary metabolite of rape Spraying tryptophan with appropriate concentration?100mg/L?on the leaf increased the content of glucosinolates in rape seedlings.Real-time analysis showed that tryptophan treatment induced the expression of transcription factor genes,promoted the expression of biaosynthesis genes,and inhibited the expression of degradation enzyme genes.This result indicated that the effect of exogenoustryptophan on the metabolism of its downstream pathway was bidirectional,on the one hand,it promoted the synthesis,on the other hand,it inhibited degradation.This is the main reason for the increase of total Indole glucosinolates.?3?Tryptophan treatment improved the resistance of rape to Cd Cl₂Tryptophan treatment can effectively alleviate the decrease of chlorophyll and the increase of membrane lipid peroxidation caused by Cd Cl₂ stress.Tryptophan inhibited the expression of Br ZIP4and Br ZIP9,two genes encoding metal ion transporters,indicating that tryptophan application in soil may affect the absorption and transportation of Cd Cl₂ and thus alleviated the damage.