Phosphorylation of chloroplast thylakoid membrane proteins does not increase the absorption cross‐section of photosystem 1

Direct measurements on the effective absorption cross‐section of photosystem (PS) 1 were obtained with control (light — ATP) and phosphorylated (light + ATP) chloroplast thylakoids from spinach. The rate of light absorption by PS1 was invariant in control and phosphorylated thylakoids, suggesting a constant functional antenna size for this photosystem. We conclude that phosphorylated chlorophyll a‐b light‐harvesting complex from PS2 is not functionally connected with the antenna pigment of PS1.