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

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 <i>calcium-adenosine triphosphate</i>, <i>calmodulin-dependent protein kinase-related kinase</i>, and <i>calmodulin-dependent protein</i> 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.