It is clear that in spite of a growing public and commercial interest and the success of several pilot studies and field scale applications more fundamental research still is needed to better exploit the metabolic diversity of the plants themselves, but also to better understand the complex interactions between contaminants, soil, plant roots, and microorganisms (bacteria and mycorrhiza) in the rhizosphere. Further, more data are still needed to quantify the underlying economics, as a support for public acceptance and last but not least to convince policy makers and stakeholders (who are not very familiar with such techniques).

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.

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The herbicide imazamox may provoke temporary yellowing and growth retardation in IMI-R sunflower hybrids, more often under stressful environmental conditions. Although, photosynthetic processes are not the primary sites of imazamox action, they might be influenced; therefore, more information about the photosynthetic performance of the herbicide-treated plants could be valuable for a further improvement of the Clearfield technology. Plant biostimulants have been shown to ameliorate damages caused by different stress factors on plants, but very limited information exists about their effects on herbicide-stressed plants. In order to characterize photosynthetic performance of imazamox-treated sunflower IMI-R plants, we carried out experiments including both single and combined treatments by imazamox and a plant biostimulants containing amino acid extract. We found that imazamox application in a rate of 132 μg per plant (equivalent of 40 g active ingredient ha−1) induced negative effects on both light-light dependent photosynthetic redox reactions and leaf gas exchange processes, which was much less pronounced after the combined application of imazamox and amino acid extract.

Barley (Hordeum vulgare L. cv. CE9704) plants grown in sand culture were exposed to increasing cadmium (Cd) (0, 14, 28, and 42 mg Cd kg À1 sand) or copper (Cu) (0, 5, 10, and 15 mg Cu kg À1 sand) concentrations for a duration of 10 days. The effect of excess Cd or Cu on plant growth, selected mineral elements content, leaf gas exchanges, and chlorophyll content were studied. The excess of Cd or Cu inhibited relative growth rate (RGR) of barley plants mainly through net assimilation rate (NAR) retardation, but leaf area ratio (LAR) was barely affected or unaffected. After 10 days of exposure, the shoot content of Cd and Cu was about 1=10 (Cu) to 1=20 (Cd) that of roots. Cadmium-and Cu-treated plants with equal RGR inhibition had some differences in photosynthesis response and in the content of some nutrients, which were not distinctive enough. Stomatal limitation to photosynthesis in Cd-treated plants was well expressed, but in Cu-treated plants factors limiting photosynthesis were more related with mesophyll constraints. Cadmium and Cu treatment reduced the chlorophyll content, relative to untreated plants more probably through degradation of photosynthetic components. In conclusion, among observed physiological disturbances in Cd and Cu-treated barley plants with relatively equal growth inhibition, the similarities prevailed over the differences.

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