The effects of NaCl and Ca on the physiology and performance of leaves of sorghum plants (Sorghum bicolor L. moench, cv. ''NK 265'') were investigated. While most of the current information on plant response to salinity comes from studies of whole plants or entire leaves, the present study uses a developmental approach and concentrates on the growing region of the leaf, to study possible role of mineral elements in growth inhibition. The physiological variables are analyzed on a mm scale and the effects of salinity therefore relate to tissue developmental stage. The performance of successive leaves differing in age, length and onset of salt treatment were evaluated. The methods of growth kinematics were applied to evaluate the distribution of growth within the developing leaf. Salinity reduced the growth rate by shortening the leaf growth zone and reducing the peak value of the relative elemental growth rate (REG rate). The beneficial effects of elevated Ca concentrations under saline conditions were quantified. Supplemental Ca restored the length of the growing region and increased the magnitude of the REG rate. The detailed growth analysis provided the basis for investigation of physiological mechanisms that act to reduce or restore leaf growth.

Spatial and temporal profiles of element concentrations and deposition rates were analyzed along the growing and mature regions of the leaf and compared to distributions of growth. Na, K, Ca and Mg concentrations and deposition rate profiles were altered by exposure to saline stress. Ca and K concentrations in the expanding tissue were largely reduced. Supplemental Ca resulted in a marked elevation of both Ca and K concentrations of the salinized leaves growing regions and restoration of growth. Since the increase in Ca and K concentrations was higher in the older, rapidly transpiring leaves and so was the improvement of growth, we suggest that improved Ca and K nutrition under conditions of saline stress and elevated Ca, play an important role in preventing growth inhibition. Na preferentially accumulated in the basal part of the leaf. Since this is a region of increased tissue growth, we concluded that high levels of sodium in the tissue were not the cause of growth inhibition in the sorghum leaf. The lack of toxic effects of Na concentrations 250-370 times higher than in the control suggests its localization or specific cellular compartmentation, possibly in the vacuole.