Photosystem II Heterogeneity and Long-Term Acclimation of Light-Harvesting

The main chlorophyll a/b protein complex of the chloroplast thylakoid membrane is organized into two subpopulations; one inner which is tightly bound to the photosystem II core and one outer which is bound more loosely or peripherally. In this study, changes in the LHC II com position due to long-term light acclimation were analyzed and quantified in spinach thylakoids and isolated stroma lamellae vesicles. The results show that; photosystem II located in the appressed thylakoid regions (α-centres) which have a relatively large antenna size, contains both the inner and outer LHC II with a predominance of the latter (58-70%). At low light the antenna size o f the α-center becomes larger due to a specific increase of the outer pool o f LHC II. The antenna size of photosystem II in the stroma thylakoids (β-centres) is smaller and contains mainly or only the inner LHC II pool. In contrast to the α-centres the β-centres centres do not undergo adaptive changes in their size in response to long-term changes in the light intensities.