The Effects Of Exogenous Glutathione On Glucosinolate Synthesis In Pakchoi Under Sulphur Deficiency

Sulphur is an essential nutrient for plant growth and development.It is a component of vitamins,peptides,sulphur-containing amino acids,and many secondary metabolites.Glucosinolates(GS)are important nitrogen-and sulphur-containing secondary metabolites widely present in Brassicaceae plants.Sulphur deficiency largely hinders the growth and development of plants,and the sulphur assimilation products such as Cys,GSH,Met and PAPS in plants cannot be effectively synthesized,which further hinders the synthesis of GS.Glutathione(GSH)is a biologically active substance with important physiological functions.It not only provides raw materials for the synthesis of GS,but also may be involved in the regulation of GS synthesis.In this study,Pakchoi was used as the experimental materials,after 17 days of sulphur deficiency,the leaves of Pakchoi were sprayed with 25 mg/L of GSH and 25mg/L of GSSG.To analyze the effects of exogenous GSH and GSSG treatment on the growth,glutathione metabolism,GS synthesis and nascent sulphur metabolism of Pakchoi under sulphur deficiency,and comprehensive analysis the effects of exogenous glutathione treatment on GS synthesis and regulatory pathways of Pakchoi under sulphur deficiency.The main conclusions are as follows:(1)Short-term sulphur deficiency had no significant effect on the growth of Pakchoi shoots,but promoted the growth of Pakchoi roots;Sulphur deficiency significantly reduced the content of most individual GS in Pakchoi and the expression of key genes in GS synthesis,and had no significant effect on the total aliphatic and total GS content,reduced the content of aromatic GS.Therefore,the total GS content decreased;significantly reduced the BcGSH1 gene expression,Cys and GSH content,?-ECs,GR and GST activity,but the expression of nascent sulphur metabolism gene is up-regulated,and the expression level of BcAPK gene is decreased.(2)Exogenous treatment of 25 mg/L GSH had no significant effect on the growth of Pakchoi shoots,but the growth of fresh weight and dry weight of Pakchoi roots had a certain delay.Most of the key genes of GS synthesis in Pakchoi under sulphur deficiency showed different degrees of up-regulation and decreased,which promoted the synthesis of aromatic,partially aliphatic GS and indole GS,but also inhibited the synthesis of some aaliphatic GS and indole GS,so the total GS content decreased;Exogenous GSH significantly increased the Cys and GSH contents of Pakchoi,and increased the activities of GR,GPx and GST.The expression of Bc GSH1 and primary sulphur metabolism genes decreased temporarily and then decreased.(3)The exogenous treatment of GSSG is similar to the GSH treatment,the growth of Pakchoi shoots was not significant,however,the growth of fresh weight and dry weight of Pakchoi roots has a certain delay,increased the expression of major GS biosynthetic genes,aromatic and partial aliphatic GS have increased,but have not reached significant levels,promoted the synthesis of aromatic GS,reduced the indole GS and total GS content.The content of Cys and GSH increased,the activity of GR and GST increased,and there was no significant effect on the metabolism of primary sulphur.However,the expression of BcAPK gene was transiently increased and then decreased.(4)Exogenous GSH and GSSG can be used as a source of sulfur to regulate the expression of primary sulphur metabolism genes,increase the content of Cys and GSH in Pakchoi,increase the activity of GR,GPx and GST,alleviate sulphur deficiency,and the effect of GSH is better than GSSG.