Pre-sowing Seed Treatment with 24-Epibrassinolide Ameliorates Pesticide Stress in Brassica juncea L. through the Modulation of Stress Markers

Abstract

The present experiment was designed to assess the effects of seed soaking with 24-epibrassinolide (EBR) on the physiology of Brassica juncea L. seedlings grown under imidacloprid (IMI) toxicity. Application of EBR increased the length of seedlings, dry weight, and pigment contents, polyphenols, total phenols, and organic acids under IMI toxicity. The expression of genes coding key enzymes of pigment, phenols, polyphenols, and organic acid biosynthetic pathways was also studied including CHLASE (chlorophyllase), PSY (phytoene synthase), CHS (chalcone synthase) and PAL (phenylalanine ammonialyase), CS (citrate synthase), SUCLG1 (succinyl Co-A ligase,), SDH (succinate dehydrogenase), FH (fumarate hydratase), MS (malate synthase). Multiple linear regression (MLR) analysis revealed that IMI application regressed negatively on seedling length, dry weight and total chlorophyll content. However, EBR seed treatment regressed positively on all the parameters studied. Moreover, interaction between IMI and EBR showed positive regression for growth parameters, content of pigments, total polyphenol, total phenol and malate, and expression of PSY and PAL. Negative interactions were noticed for the contents of fumarate, succinate and citrate, and expression of CHS and all genes studied related to organic acid metabolism. In conclusion, EBR enhanced the growth and contents of all studied metabolites by regulating the gene expression of B. juncea seedlings under IMI stress.

Keywords: GC-MS; HPLC; brassinosteroids; mustard; phenylalanine ammonialyase; pigments; total phenols.

Figure 1

Effect of seed soaking with 24-epibrassinolide (EBR) on pigment and phenol contents in Brassica juncea seedlings grown under imidacloprid (IMI) toxicity. Data are mean ± standard deviation, two-way ANOVA, and Tukey's HSD (three biological replicates). Treatments with same letter indicates no significant difference at p < 0.05. F1, F2, and F3 are F-ratios for IMI, EBR, and IMI × EBR, respectively. CN, control; H, 100 nM EBR; T1, 150 mg IMI/L DW; T2, 200 mg IMI/L DW; and T3, 250 mg IMI/L DW. ^** and ^*** indicate significant at p < 0.01 and p < 0.001, respectively.

Figure 2

Effect of seed soaking with 24-epibrassinolide (EBR) on gene expression of Brassica juncea seedlings grown under imidacloprid (IMI) toxicity. Data are mean ± standard deviation, two-way ANOVA and Tukey's HSD (three biological replicates). Treatments with same letter indicates no significant difference at p < 0.05. F1, F2, and F3 are F-ratios for IMI, EBR, and IMI × EBR, respectively. CN, control; EBR, 100 nM EBR; IMI, 200 mg IMI/L DW; CS, citrate synthase; SUCLG1, succinyl Co-A ligase; SDH, succinate dehydrogenase; FH, fumarate hydratase; MS, malate synthase; CHLASE, chlorophyllase; PSY, phytoene synthase; CHS, chalcone synthase; and PAL, phenylalanine ammonialyase. ^*, ^**, and ^*** indicate significant at p < 0.05, p < 0.01, and p < 0.001, respectively.