A comparative study of the effects of exposure to high Cd²⁺ (50 µM) and excess Zn²⁺ (600 µM) on photosynthetic performance of hydroponically-grown durum wheat seedlings was performed. At day 8, Cd and Zn were added to the nutrient solution. After 7-days exposure, the chosen concentrations of both metals resulted in similar relative growth rate (RGR) inhibitions of about 50% and comparable retardations of the CO₂ assimilation rates (about 30%) in the second developed leaf of wheat seedlings. Analysis of chlorophyll a fluorescence indicated that both metals disturbed photosynthetic electron transport processes which led to a 4- to 5-fold suppression of the efficiency of energy transformation in Photosystem II. Non-specific toxic effects of Cd and Zn, which prevailed, were an inactivation of part of Photosystem II reaction centres and their transformation into excitation quenching forms as well as disturbed electron transport in the oxygen-evolving complex. The specificity of the Cd and Zn modes of action was mainly expressed in the intensity of the toxicity effects: despite the similar inhibitions of the CO₂ assimilation rates, the wheat photochemistry showed much more sensitivity to Cd than to Zn exposure.

The use of green plants to remove, contain, inactivate, or degrade harmful environmental contaminants (generally termed phytoremediation) is an emerging technology. In this paper, an overview is given of existing information concerning the use of plants for the remediation of metal-contaminated soils. Both site decontamination (phytoextraction) and stabilization techniques (phytostabilization) are described. In addition to the plant itself, the use of soil amendments for mobilization (in case of phytoextraction) and immobilization (in case of phytostabilization) is discussed. Also, the economical impacts of changed land-use, eventual valorization of biomass, and cost-benefit aspects of phytoremediation are treated. In spite of the growing public and commercial interest and success, more fundamental research is needed still to better exploit the metabolic diversity of the plants themselves, but also to better understand the complex interactions between metals, soil, plant roots, and micro-organisms (bacteria and mycorrhiza) in the rhizosphere. Further, more demonstration experiments are needed to measure the underlying economics, for publicacceptance and last but not least, to convince policy makers.

Fatty acid content and composition of chloroplast membranes, ethylene production associated with thylakoid lipids degradation as well as photosynthetic electron transport involving photosystems 1 and 2 were used to determine the effects of increasing Cd concentrations in the growth medium [0, 14, 28, and 42 mg (Cd) kg⁻¹(sand)] on the photosynthetic performance of barley plants (H. vulgare L., cv. CE9704). High concentrations of Cd triggered serious disturbances of the chloroplast membranes. Ethylene production increased whereas a drop of 18:3 fatty acid content occurred, indicating that Cd mediates lipid peroxidation in the thylakoids. The enhanced ethylene production could be used as an early indicator of Cd-induced membrane degradation, yet at very high concentration (42 mg kg⁻¹) Cd decreased ethylene production.

Two Salix genotypes (Salix alba, clone LUC-31—genotype I and Salix viminalis, clone STOTT—genotype II) were grown hydroponically for 14 d at increasing concentrations of cadmium (Cd) (0, 5, 10, and 15 μM) in order to study both Cd accumulation and genotype tolerance. Growth responses, photosynthetic performance, activities of metal-responsive enzymes, and changes in some nutrients content were used as evaluation criteria. The Genotype II assimilated more Cd (maximum leaf concentration 47.8± 2.9 mg Cd kg⁻¹ DW) compared with the Genotype I and, based on both morphological (root length, total biomass) and metabolic indicators (photosynthetic performance, activities of metal-responsive enzymes, changes in several nutrients), was classified as less tolerant to this heavy metal. However, it is considered to be more suitable for Cd phytoextraction, as it would compensate for its somewhat lower tolerance with its higher Cd accumulation, as well as its higher productivity under field conditions.