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ENVIRONMENTAL STRESS AND ADAPTATION

Interaction of Cadmium with Glutathione and Photosynthesis in Developing Leaves and Chloroplasts of Phragmites australis (Cav.) Trin. ex Steudel¹

Institute of Agroenvironment and Forest Biology, Via Salaria Km 29,300 00016 Monterotondo scalo (Rome), Italy (F.P., M.A.I., A.M.); and Department of Plant Biology and Environmental Biotechnology, University of Perugia, Borgo XX Giugno, 06121 Perugia, Italy (S.P.)

We investigated how the presence of cadmium (Cd) at the emergence of Phragmites australis Trin. (Cav.) ex Steudel plants from rhizomes interacted with leaf and chloroplast physiological and biochemical processes. About 8.5 nmol Cd mg^–1 chlorophyll was found in leaves, and 0.83 nmol Cd mg^–1 chlorophyll was found in chloroplasts of plants treated with 50 µM Cd. As a result, a 30% loss of chlorophyll was measured concomitantly with a comparable percentage reduction in light-saturated photosynthesis. Rubisco content and activity were lowered by 10% and 60%, respectively. Antioxidant activity was stimulated by Cd treatment and was associated with an increase in the glutathione and pyridine pools, and with a larger pool of reduced glutathione. It is suggested that the glutathione pool and its predominance in the reduced state protected the activity of many key photosynthetic enzymes against the thiophilic binding of Cd. Chloroplast ultrastructure was not significantly altered with 50 µM treatment and the efficiency of photosystem II, measured as the fluorescence ratio F_v/F_m, remained high because F₀ and F_m were proportionally decreased. In plants treated with 100 µM Cd, all effects were exacerbated, but F_v/F_m remained close to that of control leaves and the glutathione and pyridine nucleotides pools were lowered. The results suggest that glutathione exerted a direct important protective role on photosynthesis in the presence of Cd.

¹ This work was supported by the Consiglio Nazionale delle Ricerche of Italy.

^* Corresponding author; e-mail angelo.massacci{at}ibaf.cnr.it; fax 39–06–9064492.

Received May 7, 2003; returned for revision May 30, 2003; accepted June 20, 2003.

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