The bicarbonate effect, oxygen evolution, and the shadow of Otto Warburg.

A short list of the twentieth century's dominant figures in photosynthesis would unquestionably include Otto Warburg. One of his many discoveries, the 'bicarbonate effect' remains a lasting puzzle to his heirs in the field. Recent developments in this area of research have renewed interest and call for a re-examination of the ideas surrounding this controversial topic. Focus here will be on hypotheses developed by a small number of researchers who proposed that bicarbonate may be involved in oxygen evolution. The effect of bicarbonate on the acceptor side of Photosystem II (PS II) is discussed by Jack van Rensen (in this issue).