Grana formation in chloroplasts may promote energy transfer between photosystem II units.

Here we have utilised the observation [2,13] that lowering the medium pH to 5.4 brings about the formation of grana which are morphologically indistinguishable from those induced by metal cations at neutral pH values. These grana seem also to be biochemically similar to those produced by metal cations as indicated by the chlorophylls/b ratios of digitonin fractions [ 141. We now demonstrate that incubation of chloroplasts at pH 5.4 strongly favors energy transfer between photosystem II units, and suggest that this may be due to grana formation.