Detoxification of Zinc in Tobacco (Nicotiana tabacum L.) Plants: Exudation of Zn as Ca-containing Grains through the Trichomes

Abstract

Tobacco (Nicotiana tabacum L. cv. Xanthi) exposed to cadmium have been shown to excrete Cd/Ca-containing grains through their trichomes. In this work, tobaccos were exposed to various Zn and Ca concentrations. Growth tests showed that Ca has a protective effect against Zn toxicity, and the endogenous metal contents showed that Ca limited the uptake of Zn, but not the accumulation and translocation. Exposure to Zn induced an increase of the trichome density on the leaves. The grains produced by the trichomes were directly observed under variable-pressure scanning electron microscopy (VP-SEM) and isolated for further characterization. The mineralogical nature of the grains and the structural environment of Zn were determined by state-of-the-art synchrotron-based x-ray microanalyses: x-ray micro-fluorescence (XRF), x-ray micro-diffraction (micro-XRD), and micro-focused extended x-ray absorption fine structure spectroscopy (micro-EXAFS). This study shows that tobacco trichomes have an active role to discharge Zn by immobilizing it in biogenic minerals.