Stage-Specific State I-State II Transitions during the Cell Cycle of Euglena gracilis.

In synchronized Euglena gracilis (light-dark regime of 14:10 hours) the successive formation of the photosynthetic apparatus during cell ontogeny is correlated with large changes in photosynthetic efficiency (P Brandt, B von Kessel 1983 Plant Physiol 72: 616-619; B Kohnke, P Brandt 1984 Biochim Biophys Acta 766: 156-160). This observation led us to investigate the functional association of the chlorophyll a/b light-harvesting protein complex (LHCP) with photosystem I or II, because changes in energy flow to photosystem I or II and in energy transfer between the two photosystems can be a reason for these alterations. As criterion for the association of the LHCP with photosystem I or II, state transitions were determined after 15 minutes preillumination using wave-lengths of 725 or 620 nanometers. The state transitions were determined from measurements of fluorescence induction at room temperature, and fluorescence kinetics at 77 K. According to the obtained data (a) mobile LHCP is present only between the 6th and the 10th hour of the light-time of the cell cycle and (b) this functional relation of the LHCP to photosystem I only at this stage of Euglena chloroplast development is not accompanied by a decrease in stacking. A model for the organization of the newly inserted LHCP within the photosynthetic apparatus of E. gracilis is discussed.