Subcellular Distribution and Chemical Form of Cadmium in Bean Plants

Abstract

The subcellular distribution and chemical form of Cd in bean plants grown in nutrient solutions containing Cd were investigated. Cd was accumulated mainly in roots and to a minor extent in leaves. Subcellular fractionation of Cd-containing tissues (pH 7.5) showed that more than 70% of the element was localized in the cytoplasmic fraction in roots as well as in leaves. Little Cd (8 to 14%) was bound either to the cell wall fraction or to the organelles. Gel filtration of the soluble fraction showed Cd to be associated mainly with 5,000 to 10,000 molecular weight components in roots, and 700 to 5,000 molecular weight components in leaves. Small amounts of Cd were found in the high molecular weight proteins (molecular weight 150,000). Only traces of Cd could be detected as a free ion. Chemical characterization of the low molecular weight components resulted in the identification of nine amino acids which were identical in roots and leaves. Cd in bean plants is assumed to be bound to peptides and/or proteins of low molecular weight.Cd is a major environmental contaminant (8,22). The essentiality of this element for either plants or animals has not yet been demonstrated, whereas its toxicity in higher concentrations is well established (8, 16). The molecular basis for this toxicity remains largely unknown. Interest has focussed primarily on the relationship between substrate parameters and plant concentration (12,20), the general toxicity symptoms (10,26), and specific effects on transpiration and photosynthesis (1, 2). Numerous in vitro and in vivo studies on the effects of Cd revealed that it is either an inhibitor or activator of enzymes, such as nitrate reductase, malate dehydrogenase, and peroxidase (16, 17). However, little is yet known about transport, intracellular localization, and binding of Cd in situ (3,5,18

Iodine biofortification of vegetable plants—An innovative method for iodine supplementation

“…Following the differential centrifugation procedure initially introduced by Weigel et al [21] we applied differential centrifugation on homogenized tissue and separated the cells of vegetables strengthened by exogenous iodine (150 mg/m 2 ) into indissoluble cytoplasm, cytoderm and organelle. The details of the procedure are shown in Figure 1.…”

Mercury intracellular partitioning and chelation in a salt marsh plant, Halimione portulacoides (L.) Aellen: Strategies underlying tolerance in environmental exposure

“…The total amount of mer cury extracted after the washes with CaCl 2 was con sid ered adsorbed mer cury. Buffer extracted mer cury com prises the sol u ble frac tion and it was assumed to be mainly cyto solic mer cury whereas the mer cury in the insol u ble frac tion was assumed as mer cury derived from cat ionic exchange sites in cell walls (Wei gel and Jäger, 1980;Khan et al, 1984).…”

Accumulated forms of thallium and cadmium inLemna minor. II. Relationship between duration of exposure and metal-protein binding

“…A similar picture has been reported in a number of other studies; for example, in soybean three proteinaceous Cd binding fractions have been identified, a high (Me > 70,000) and a low <Me -2,280) molecular weight fraction and an intermediate one of Mr 13,800 which was induced in the presence of Cd (Casterline and Barnett, 1977). Weigel and Jager (1980) demonstrated that Cd in Phaseolus vulgaris seedlings was mainly bound to peptides and low molecular weight proteins. ln cabbage and tobacco leaves an inducible Cd binding protein of Me 10,000 was reported by Wagner and Trotter (1982), similarly almost all of the Cd in aqueous extracts of lycopersicon esculentum was recovered in association with an inducible protein fraction of Me 10,000 (Bartolf et al, 1980).…”