The degree of functional separation between the two photosystems in isolated thylakoid membranes deduced from inhibition studies of the imbalance in photoactivities.

In order to examine whether the two photosystems, PS I and PS II, are organized in specific electron transporting pairs, or randomly transport electrons from PS II to PS I, the photosystems imbalance of photoactivities (Emerson enhancement) was measured by modulated fluorimetry under different degrees of PS II inhibition in broken chloroplasts, where the granal structures were preserved by the presence of 5 mM MgCl. The results indicate a lack of any measurable specific functional pairing between individual PS I and PS II, in contrast to a previous research work in leaves (Malkin et al. 1986, Photosynth. Res. 10: 291-296). These results and this discrepancy are further discussed.