Growth and development of sorghum leaves under conditions of NaCl stress: possible role of some mineral elements in growth inhibition

Abstract

Elongating leaf tissue, which in monocotyledonous species is a small region located near the leaf base, requires a continuous supply of nutrients to maintain cell expansion and is, therefore, highly susceptible to nutrient disturbances. The objective of this work was to investigate the effects of salinity on the availability of nutrient elements within the elongating region of sorghum (Sorghum bicolor [L.] Moench, cv. ‘NK 265’) leaves, in order to assess their possible role in salt-induced growth inhibition. Plants grown in complete nutrient solution were exposed to 1 or 100 mol·m−3 NaCl salinity. Spatial distributions of biomass and bulk tissue K, Na, Ca, and Mg were determined on a millimeter scale in the growth zone of leaf 6, while it was growing rapidly just after emergence from the encircling whorl of older leaf sheaths. Spatial patterns of net rates of element deposition were also calculated. Potassium, Ca, Mg, and Na exhibit along the leaf growing zone, distinct spatial concentration patterns which are changed by exposure to saline stress. Salinity induces a decrease in K concentration and deposition rate throughout the elongation zone. The inhibition of K deposition rate due to salinity increases with distance from the leaf base, as did the inhibition of growth. Salinity induces a dramatic decrease in Ca that could also be responsible for leaf growth inhibition. The concentration of Mg is lower under salt stress in the basal part of the growing region, where Na is preferentially accumulated. Since the base of the growth zone is where growth is least affected by salinity, high levels of Na are not the cause of growth inhibition in this salt-affected leaf tissue.