Methyl Jasmonate and Zinc Sulfate Induce Secondary Metabolism and Phenolic Acid Biosynthesis in Barley Seedlings

Abstract

This study aimed to reveal the impact of MeJA and ZnSO4 treatments on the physiological metabolism of barley seedlings and the content of phenolic acid. The results showed that MeJA (100 μM) and ZnSO4 (4 mM) treatments effectively increased the phenolic acid content by increasing the activities of phenylalanine ammonia-lyase and cinnamate-4-hydroxylase (PAL) and cinnamic acid 4-hydroxylase (C4H) and by up-regulating the expression of genes involved in phenolic acid synthesis. As a result of the MeJA or ZnSO4 treatment, the phenolic acid content increased by 35.3% and 30.9% at four days and by 33.8% and 34.5% at six days, respectively, compared to the control. Furthermore, MeJA and ZnSO4 treatments significantly increased the malondialdehyde content, causing cell membrane damage and decreasing the fresh weight and seedling length. Barley seedlings responded to MeJA- and ZnSO4-induced stress by increasing the activities of antioxidant enzymes and controlling their gene expression levels. Meanwhile, MeJA and ZnSO4 treatments significantly upregulated calcium-adenosine triphosphate, calmodulin-dependent protein kinase-related kinase, and calmodulin-dependent protein genes in barley seedlings. This suggested that Ca2+ may be the signaling molecule that promotes phenolic acid synthesis under MeJA and ZnSO4 treatment. This study deepens the understanding of the phenolic acid enrichment process in barley seedlings under MeJA and ZnSO4 treatments.