Zinc distribution and excretion in the leaves of the grey mangrove, Avicennia marina (Forsk.) Vierh

Mangroves are important as primary producers in estuarine food chains. Zinc is often a major anthropogenic contaminant in estuarine ecosystems and has potential ecotoxicological consequences for mangrove communities. Accumula tion, distribution and excretion of zinc in the leaf tissue of the grey man grove, Avicennia marina was studied using SEM X-ray microanalysis and Atomi c Absorption Spectroscopy. The first leaves of A. marina grown in 500 mu g Zn as ZnCl2 per g of dry soil were found to accumulate 106.3 +/- 18.5 mu g Zn per g dry tissue, significantly higher than control plants, after a 7-mo nth period. Washings from first leaves contained significantly higher amoun ts of zinc (0.30 +/- 0.14 mu g/cm(2) Zn) than control plants after 1 month, suggesting excretion of zinc from glandular trichomes. SEM X-ray microanal ysis revealed salt crystals exuded from glandular tissue on the adaxial sur face of first leaves to be composed of alkaline metals and zinc in zinc tre ated plants. SEM X-ray microanalysis of seedlings dosed with 4 g/l Zn as Zn Cl-2 revealed a decreasing Zn gradient from xylem tissue, through photosyn thetic mesophyll, to hypodermal (water) tissue. A subsequent increase in Zn concentration was observed in glandular tissue. Cell wall Zn concentration s were consistently higher than intracellular Zn concentrations. (C) 1999 E lsevier Science B.V. All rights reserved.