Cellular distribution of copper, lead and zinc in the grey mangrove, Avicennia marina (Forsk.) Vierh

The distribution and excretion of Cu, Pb and Zn in the root and leaf tissue of the grey mangrove, Avicennia marina was studied using scanning electron microscope (SEM) X-ray microanalysis and atomic absorption spectroscopy. S EM X-ray microanalysis of nutritive root tissue in seedlings dosed with 4 g /l Cu, Pb and Zn revealed accumulation of all metals predominantly in cell walls. The root epidermis provided a major barrier to the transport of Pb o nly. The endodermal casparian strip was shown to provide a barrier to movem ent of all three metals into the stele. Washings from mature leaves contain ed significantly higher amounts of Zn and Cu than control plants after 1 mo nth, suggesting excretion of both metals from the glandular trichomes. In a ddition, salt crystals exuded from the glands on the adaxial surface of mat ure leaves were composed of alkaline metals. Zn in Zn-treated plants, and C u in Cu-treated plants. Leaf tissue in seedlings dosed with 4 g/l Zn showed a decreasing gradient of the metal from xylem tissue, through photosynthet ic mesophyll, to hypodermal (water) tissue, with a subsequent increase in c oncentration in the glandular tissue. A similar gradient was observed acros s leaf tissue in seedlings dosed with 4 g/l Cu, however, there was no subse quent increase in Cu concentration in glandular tissue. For both metals lea f cell wall metal concentrations were consistently higher than intracellula r concentrations. (C) 2000 Elsevier Science B.V. All rights reserved.