Light-induced changes in the conformation and configuration of the thylakoid membrane of Ulva and Porphyra chloroplasts in vivo.

The ultrastructural basis of light-induced transmission and light scattering changes of thalli of Ulva and Porphyra were investigated by high resolution electron microscopy and microdensitometry. The results show that upon illumination of dark thalli (a) a reduction in thickness of thylakoid membranes (conformational change), (b) a more regular ordering, and (c) flattening of the thylakoids (configurational changes) have occurred. An explanation for the observed conformational and configurational changes was proposed in terms of correlated changes in ionic environment and osmotic properties of chloroplasts in vivo which are initiated by photosynthetic reactions.