Role of Ca2+ in phenolic compound metabolism of barley (Hordeum vulgare L.) sprouts under NaCl stress

Abstract

Background: The literature on the role of calcium ion (Ca²⁺ ) in relation to phenolic compounds metabolism and related enzymes activities remains controversial. It is still unclear whether Ca²⁺ affects phenolic compounds content of barley sprouts. This study investigated the role and function of Ca²⁺ in phenolic compound metabolism of barley (Hordeum vulgare L.) sprouts under sodium chloride (NaCl) stress.

Results: Calcium chloride (CaCl₂ ) significantly improved total calcium and calmodulin (CaM) contents as well as Ca²⁺ concentration, and enhanced phenolic compound accumulation by regulating the gene, protein expression and the activities of enzymes related to phenolics biosynthesis. Specifically, CaCl₂ 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 CaCl₂ treatment. Conversely, lanthanum(III) chloride (LaCl₃ ), ethylene glycol tetraacetic acid (EGTA) and 2-aminoethoxydiphenyl borate (2-APB) induced opposite effects. Decreased calcium and CaM contents and Ca²⁺ 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 Ca²⁺ influx and release from apoplast and intracellular stores, respectively. © 2019 Society of Chemical Industry.

Keywords: Ca2+ concentration; NaCl stress; barley sprout; calcium; phenolic compound.