Ion gradients and adenosine triphosphatase localization in the salt glands of Avicennia marina (Forsskål) Vierh.

Abstract

Possible sites of iron pumping associated with glandular salt excretion from the leaf of the mangrove Avicennia marina were investigated using energy-dispersive X-ray analysis and ATPase cytochemistry. The collecting cells of the gland had low sodium and chlorine ratios and high potassium ratios. This contrasted with the stalk/excretory cells of the gland which had very high chlorine ratios and lower potassium ratios. Considerable ATPase activity was localized at the stalk cell plasmalemma in the region of the stalk cell / collecting cell interface, and at the collecting cell plasmalemma. It is suggested that these are sites of active ion influx into the gland. The low chlorine ratio within the collecting cells by comparison to the xylem vessels and the surrounding spongy mesophyll suggests that the collecting cells are at the endpoint of a symplastic and possibly an apoplastic downhill ion gradient. ATPase activity associated with the plasmalemma of the excretory cells suggests that efflux from the gland is also an active process.