M. D. Vázquez

Localization of zinc and cadmium in Thlaspi caerulescens (Brassicaceae), a metallophyte that can hyperaccumulate both metals

Summary The compartmentation of Zn and Cd in roots of Thlaspi caerulescens J. & C. Presl, a metallophyte that hyperaccumulates both metals, was investigated by means of EDAX. Two methods for sample preparation, Na 2 S-fixation and freeze-substitution, were compared. Na 2 S-fixation was not suitable for preventing the loss of metal ions from the samples. According to our results from freeze-substituted samples, Cd accumulated mainly in the apoplast and, to a lesser extent, in vacuoles, whereas Zn was principally found in vacuoles and, to a lesser extent, in cell walls.

Chromium III‐iron interaction in iron sufficient and iron deficient bean plants. II. Ultrastructural aspects

Abstract The influence of a growth stimulating low Cr III concentration (1.0 μM) on chloroplast ultrastructure, the Fe, Cr, and Mn content of chloroplast extracts, o‐phenantroline extractable leaf Fe, and catalase activity was studied in both Fe‐sufficient and Fe‐deficient bush bean (Phaseolus vulgaris L.) plants. Chromium supply hardly affected the chloroplast ultrastructure of Fe‐sufficient plants but significantly improved chloroplast ultrastructure in Fe‐deficient leaves. Generally, Cr supply did not significantly influence chloroplast Fe‐content, but increased the Fe/Mn ratio in Fe‐deficient chloroplasts. In leaves from Fe‐deficient plants, o‐phenantroline extractable Fe was significantly increased, while catalase activity was not significantly influenced by Cr supply. The possible mechanisms of the beneficial effects of Cr III in Fe‐deficient plants are discussed.

Technetium-99 toxicity in phaseolus vulgaris: Ultrastructural evidence for metabolic disorders

The influence of light intensity on the effects of 10−6 mol L−199Tc on growth, chlorophyll and carotenoid contents of bush bean plants was investigated. After germination and cotyledon excision, the plants were grown in a growth chamber either under low light (photosynthetic active radiation, PAR 144 μE m−2 s−1) or higher light (PAR 307 μE M−2 s−1) conditions. In plants grown under the higher light conditions, 99Tc hardly affected CO2-assimilation, dark respiration, pigment contents and growth. No toxicity symptoms were observed in these plants. Under low light conditions, 99T c significantly decreased growth and the concentration of chlorophylls. Toxicity symptoms in the form of chlorosis and necrosis developed. Transmission electron microscopy (TEM) observations revealed alterations of chloroplast ultrastructure comparable to those described for plants slightly affected by paraquat toxicity or by Mo-deficiency. Our results indicate that in the low light plants 99Tc induces damage in chloroplasts by peroxidation of membrane lipids.

Phytotoxic effects of technetium-99 in beans: Influence of cotyledon excision

Abstract The influence of cotyledon excision on the effects of 99 Tc on Tc accumulation, growth and ultrastructure of bean seedlings was studied. In plants with or without cotyledons, 99 Tc accumulated principally in leaves, although leaves of plants without cotyledons showed a significantly higher 99 Tc concentration. Cotyledon excision substantially enhanced the toxic effects of 99 Tc on growth. Light, scanning and transmission electron micrographs from 99 Tc-treated plants without cotyledons display increased autophagic vacuole activity, accumulation of protein bodies in roots, and decreased starch content and severe ultrastructural alterations in chloroplasts. Our results support the hypothesis that 99 Tc toxicity is mainly associated with anabolic processes in developing tissues.

Accumulation and Distribution of 99 Tc in three Bean Plant Varieties

In nature technetium-99 ( 99Tc) exists in very small amounts as a product of the spontaneous fission of 235U (1). The potencial entrances of 99Tc into the environment are principally arise from the nuclear fuel cycle, which yields high amounts of this isotope by slow neutron fission of 235U and 239pu (6.3 and 6.1 % respectively) (2), and from nuclear weapons, hospitals and research institutions.