Investigation of metal exudates from tobacco glandular trichomes under heavy metal stresses using a variable pressure scanning electron microscopy system

Abstract

Tobacco (Nicotiana tabacum) was recently shown to detoxify heavy metals by exudation of metals as a metal-substituted calcite (calcium carbonate) through leaf trichomes. In this paper, we describe the applications of the variable-pressure scanning electron microscopy (VP-SEM) system to investigate tobacco trichomes exudates after heavy metal treatment. An energy-dispersive X-ray analysis (EDX) system fitted to VP-SEM revealed that the exudates contain amounts of heavy metals. Overexpression of cysteine synthase confers cadmium (Cd) tolerance to tobacco, and the endogenous concentration of Cd was 20% less in transgenic plants than in wild-type plants. We evaluated the numbers of trichomes on the leaf surfaces of wild-type and transgenic plants using VP-SEM. The numbers of both long and short trichomes in the transgenic plants were 25% higher than in that of wild-type plants, indicating the active excretion of Cd from trichomes in transgenic plants. The VPSEM-EDX system is a powerful tool to investigate plant epidermal structures and functions.