Role of Ca 2+ in phenolic compound metabolism of barley ( Hordeum vulgare L.) sprouts under NaCl stress

BACKGROUND The literature on the role of calcium ion (Ca 2+ ) in relation to phenolic compounds metabolism and related enzymes activities remains controversial. It is still unclear whether Ca 2+ affects phenolic compounds content of barley sprouts. This study investigated the role and function of Ca 2+ in phenolic compound metabolism of barley ( Hordeum vulgare L.) sprouts under sodium chloride (NaCl) stress. RESULTS Calcium chloride (CaCl 2 ) significantly improved total calcium and calmodulin (CaM) contents as well as Ca 2+ concentration, and enhanced phenolic compound accumulation by regulating the gene, protein expression and the activities of enzymes related to phenolics biosynthesis. Specifically, CaCl 2 significantly increased the activities of phenylalanine ammonia lyase (PAL), cinnamic acid 4‐hydroxylase (C4H), 4‐coumarate coenzyme A ligase (4CL) and ferulic acid 5‐hydroxylase (F5H) by up‐regulating the corresponding protein expression. The activity of p ‐coumaric acid 3‐hydroxylase (C3H) decreased during germination while caffeic acid O‐methyltransferase (COMT) increased initially and then decreased, which was consistent with the changes in gene and protein expression under CaCl 2 treatment. Conversely, lanthanum(III) chloride (LaCl 3 ), ethylene glycol tetraacetic acid (EGTA) and 2‐aminoethoxydiphenyl borate (2‐APB) induced opposite effects. Decreased calcium and CaM contents and Ca 2+ concentration were observed, and fluctuation change of relevant gene and protein expressions and PAL, C4H, 4CL, C3H, COMT and F5H activitives were also detected. CONCLUSION Calcium ion played an important role for mediating NaCl stress‐induced phenolics accumulation in barley sprouts. It required both Ca 2+ influx and release from apoplast and intracellular stores, respectively.