Copper and photosystem II: A controversial relationship

Copper is an essential micronutrient for higher plants and algae and has a direct impact on photosynthesis. It is a constituent of the primary electron donor in photosystem I, the Cu‐protein plastocyanin. Many authors have also described Cu as a constituent of photosystem II (PSII). However, high Cu concentrations inhibit the photosynthetic electron transport, especially in PSII. In addition, both Cu deficiency and Cu toxicity interfere with pigment and lipid biosynthesis and, consequently, with chloroplast ultrastructure thus negatively influencing the photosynthetic efficiency. In this review, the different functions proposed for the metal in PSII are reviewed. With reference to the effect of toxic Cu on PSII, the polemic results concerning its mechanism of action and Cu‐binding sites are discussed. Other effects of Cu toxicity and Cu deprivation on the thylakoid membrane are also briefly described.