Quantum efficiency of photosynthetic energy conversion.

Abstract

The quantum efficiency of photosynthetic energy conversion was investigated in isolated spinach [Spinacia oleracea] chloroplasts by measurements of the quantum requirements of ATP formation by cyclic and noncyclic photophosphorylation catalyzed by ferredoxin. ATP formation had a requirement of about 2 quanta/1 ATP at 715 nm (corresponding to a requirement of 1 quantum/electron) and a requirement of 4 quanta/ATP (corresponding to a requirement of 2 quanta/electron) at 554 nm. When cyclic and noncyclic photophosphorylation were operating concurrently at 554 nm, a total of about 12 quanta was required to generate the 2 NADPH and 3 ATP needed for the assimilation of 1 CO2 to the level of glucose.