Effects of calcium application on the salt tolerance and sodium excretion from salt glands in zoysiagrass (Zoysia japonica)

Abstract

AbstractZoysiagrass (Zoysia japonica Steud.), a native grass in Japan, is a warm‐season turfgrass displaying high salt tolerance, mainly derived from salt excretion through salt glands. The present study focused on how external calcium (Ca) affects sodium (Na) excretion from salt glands to relieve salt stress, including response to oxidative stress, and discussed the physiological mechanisms possibly involved. Treatments using 0, 25, 50, 75, 100, 125 and 150 mmol/L sodium chloride (NaCl), with or without applying 2 or 10 mmol/L calcium chloride (CaCl2), were conducted for seven days. Growth inhibition and an abrupt increase in Na excretion from salt glands occurred above 100 mmol/L NaCl treatment, while Na concentrations in shoot and root tissues increased with increasing NaCl concentration from 0 to 75 mmol/L treatment. Above 100 mmol/L NaCl treatment, pectic acid‐binding Ca and glycinebetaine concentrations decreased in shoot and root tissues, but free proline concentration and the activities of plasmalemma ATPase, catalase (CAT) and ascorbate peroxidase (APX) increased. Calcium application alleviated growth inhibition when added to high level of NaCl treatments (over 100 mmol/L NaCl). Compared to the treatment without Ca, Na concentration in shoot and root tissues and ATPase activity in the root decreased, but Na exclusion from salt glands, pectic acid‐binding Ca concentration in shoot and root tissues, and ATPase, CAT and APX activities in the shoot increased. Thus, Na excretion through salt glands seems to occur when Na concentration in the plant exceeds its accumulation limit, and this salt tolerance reaction involving salt glands proceeds in two steps: the grass absorbs and accumulates Na in the shoot and root up to a threshold, above which Na is removed through salt glands. Calcium application promoted Na excretion through salt glands, especially under growth‐inhibiting Na concentrations, which might be induced by the increase in extracellular excretion of Na by plasmalemma ATPase.