Distribution of elements on tobacco trichomes and leaves under cadmium and sodium stresses

When tobacco (Nicotiana tabacum) plants are exposed to toxic level of cadmium (0.2 mM Cd), their trichomes actively excrete crystals (Choi et al., 2001). In this study, we investigated the distribution of Cd and NaCl on trichomes and leaf surfaces. Energy dispersive x-ray (EDX) analysis revealed that, under toxic Cd stress, crystals exudated from the trichomes contained high amounts of Ca, Mg, and Cd, as well as low levels of P, S, and Mn. Electron spectroscopic imaging (ESI) from trichomes and attached crystals showed that these crystals emitted denser radiation energy for Ca and Cd than did the head cells of the trichomes. However, no Cd was detected on the trichome surface itself or within the leaf epidermis. In contrast, treatment with salt (NaCl) did not stimulate crystal formation; instead, it induced the abnormal expansion of trichome cells. Although Na was not accumulated within the crystals, a considerable amount of both Na and Cl was sequestered within the stalk cells of the long trichomes. Therefore, we believe that tobacco trichomes play an important role in Cd crystal exudation through crystallization, but that, under NaCl stress, the long trichomes sequester those elements within their stalks.