Morphology and Ultrastructure of the Salt Glands on the Leaf Surface of Rhodes Grass (Chloris gayana Kunth)

Abstract

We examined the morphology, distribution, and ultrastructure of the salt glands of Rhodes grass (Chloris gayana Kunth), Poaceae, under conditions of salinity (0–400 mM). Salt glands excreted Na+ after exposure to salinity, and nearly twice the amount of Na+ contained in the leaf was excreted in 1 wk under 400 mM NaCl treatment. Salt glands were distributed above the small veins on the adaxial surface and between the veins on the abaxial surface. Macrohairs were distributed on the same lines as the salt glands. Salt gland density increased with NaCl treatment concentrations, suggesting an acclimation to promote salt excretion under high salinity. A salt gland consisted of two cells, the basal cell and the cap cell. Distinctive membranes run longitudinally from the plasma membrane at the apical region of the basal cell and existed as bended sheets. The sheets were swollen in the bottom region of the basal cell but were not connected with the plasma membrane in this region. The occurrence of abundant mitochondria in the gland cells suggests that salt transport is an energy-requiring process. Possible mechanisms of salt excretion are discussed, along with previous findings.