Comparison of the toxicity and distribution of cadmium and lead in plant cells

Abstract

The toxicity of heavy metals (Cd, Zn, and Pb) was assessed by in vivo observations of their effect on cytoplasmic streaming in Allium cepa L. bulb scale epidermal cells. On the basis of our results, the order of toxicity of the studied cations is Zn < Pb << Cd. The difference in toxicity between cadmium and lead was found to be very large. When cytoplasmic streaming was assessed, this difference was threefold. When the total content of cadmium and lead (determined by inductively coupled plasma mass spectrometry) was the criterion, the difference in toxicity was 15-fold. Fractionation of the tissue and enzymatic digestion of the cells revealed that the largest proportion of cadmium was located in the cell walls (56%), whereas almost all of the lead (97.6%) was accumulated in an insoluble form. The speciation of water-soluble Pb and Cd fractions is discussed on the basis of analysis by capillary zone electrophoresis interfaced with inductively coupled plasma mass spectrometry of water extracts from epidermal cells. Lead and cadmium appeared to be bound mainly to salts, which explains their toxicity. Cadmium was complexed (detoxified) by organic acids, while thiols were the metal-complexing species for lead. Histidine formed complexes with both cadmium and lead. Ultrastructural analyses showed that lead was encapsulated in small vesicles in the cytoplasm. Fluorescence studies of the endoplasmic reticulum (ER) revealed that it underwent extensive fragmentation under the influence of lead, with numerous ER vesicles appearing in the cells. In other words, the lead deposits in the cytoplasm were contained in vesicles arising from fragmentation of the ER. These observations indicate that epidermal cells have a rapid and effective mechanism for detoxifying lead involving the ER, and this may be one of the mechanisms accounting for the lower toxicity of lead in comparison with cadmium. The suitability of Allium cepa bulb scale epidermal cells for use in ecotoxicological studies is also discussed. Step-by-step directions for this test are given.

Salix matsudana Koidz Tolerance Mechanisms to Cadmium: Uptake and Accumulation, Subcellular Distribution, and Chemical Forms

“…The results obtained here are consistent with earlier findings [7,11,31,32]. However, Carrier et al [33] reported that approximately 80% of Cd was found predominantly in the soluble fraction, and relatively little Cd was found in the cell wall (11%).…”

“…The data from inductively coupled plasma mass spectrometry (ICP-MS) revealed that 56% of total Cd was located in cell walls of Allium cepa epidermal cells exposed to Cd [31]. Similarly, the data from energydispersive x-ray analyses (EDXA) indicated that Cd ions appeared in walls of root cells of A. cepa treated with Cd [42].…”

Does zinc concentration in the substrate influence the onset of flowering in Arabidopsis arenosa (Brassicaceae)?

“…Both metals have similar chemical properties: they have similar atomic radius, similar oxidation state in chemical compounds and share similar geochemical properties (Emsley 1991;Kabata-Pendias 2010) and both have been evidenced to interact similarly with different marcomolecules in plant cells (e.g. Przedpelska-Wasowicz et al 2012;PrzedpelskaWasowicz and Wierzbicka 2011;Wierzbicka et al 2007). Taking this into account, similar mechanism could be postulated for both phenomena.…”

Lead Uptake, Toxicity, and Detoxification in Plants

“…The lead, that could be bound by certain organic molecules (Piechalak et al 2002;Vadas and Ahner 2009), is sequestered in several plant cell compartments: vacuoles (Małecka et al 2008;Meyers et al 2008), dictyosome vesicles (Malone et al 1974), endoplasmic reticulum vesicles (Wierzbicka et al 2007), or plasmatubules (Wierzbicka 1998).…”