Effects of exogenous calcium on the drought response of the tea plant (<i>Camellia sinensis</i> (L.) Kuntze)

Abstract

Under drought stress, leaf electrolyte leakage differed significantly, indicating greater damage to cell membranes in control plants than in Ca-treated plants. Calcium application resulted in greater pH of cell sap; higher accumulation of tyrosine, methionine, and valine; and a greater Mg²⁺ content as compared to control plants. Drought stress downregulated most of the quality-related genes in both groups of tea plants. By contrast, significant upregulation of some genes was observed, namely <i>CRK45</i>, <i>NAC26</i>, <i>TPS11</i>, <i>LOX1</i>, <i>LOX6</i>, <i>Hydrolase22</i>, <i>DREB26</i>, <i>SWEET2</i>, <i>GS</i>, <i>ADC</i>, <i>DHN2</i>, <i>GOLS1</i>, <i>GOLS3</i>, and <i>RHL41</i>. Among them, three genes (<i>LOX1</i>, <i>RHL41</i>, and <i>GOLS1</i>) showed 2-3 times greater expression in Ca-treated plants than in control plants. Based on these results, it can be speculated that calcium affects galactinol biosynthesis and participates in the regulation of stomatal aperture not only through activation of abscisic-acid signaling but also through jasmonic-acid pathway activation. These findings clarify calcium-mediated mechanisms of drought defense in tree crops. Thus, calcium improves the drought response in the tea tree.