COPPER AND PHOTOSYSTEM-II - A CONTROVERSIAL RELATIONSHIP

Copper is an essential micronutrient far higher plants and algae and h as a direct impact on photosynthesis. It is a constituent of the prima ry electron donor in photosystem I, the Cu-protein plastocyanin. Many authors have also described Cu as a constituent of photosystem II (PSI I). However, high Cu concentrations inhibit the photosynthetic electro n transport, especially in PSII. In addition, both Cu deficiency and C u toxicity interfere with pigment and lipid biosynthesis and, conseque ntly, with chloroplast ultrastructure thus negatively influencing the photosynthetic efficiency. In this review, the different functions pro posed for the metal in PSII are reviewed. With reference to the effect of toxic Cu on PSII the polemic results concerning its mechanism of a ction and Cu-binding sites are discussed. Other effects of Cu toxicity and Cu deprivation on the thylakoid membrane are also briefly describ ed.