Photosystem II (PSII) from Cu‐deficient pea plants (Pisum sativumL., cv. Lincoln) has been investigated for electron transport activity, Cu content, and changes in some lipid components. Total fatty acid content was lower that in control plants, with an additional shift in the C18fatty acid patterns. Less α‐linolenic and more linoleic and oleic acids were found. PSII preparations from Cu‐depleted plants showed a decreased carotenoid content in light harvesting chlorophylla/bcomplex of photosystem II (LHCII) and additional variations in pigment composition of pigment‐protein complexes. In the green algaDunaliellathe effect of Cu deficiency on fatty acid composition was similar to that in pea plants, but the influence on the carotenoid pattern was much less pr