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Development and Repair of Photosystem II Activity in Normal and Chloramphenicol-treated Euglena gracilis Cells ¹

Michael Gurevitz and Itzhak Ohad

Department of Structural Chemistry and Biochemistry, The Weizmann Institute of Science, Rehovot, Israel, Department of Biological Chemistry, The Hebrew University, Jerusalem, Israel

Photosystem II activity, development, and organization were studied in membranes from dark-adapted Euglena gracilis Klebs var. Z Pringsheim cells during a modulated greening process of light-dark-light cycles. The results obtained from measurements of overlapping partial photosystem II (PSII) reactions (fluorescence induction parameters, quantum yield, flash yield, and maximal rate of H₂O 2,6-dichlorophenolindophenol [DCIP] and 1,5-diphenylcarbazide [DPC] DCIP reactions) during these cycles indicate the formation of active PSII units in the dark. The necessity for proteins from the chloroplast translational machinery for this formation is evidenced by the inhibition of synthesis of the PSII units in chloramphenicol-treated cells. The effect of this drug, both during the dark and second light periods, can be summarized as follows: (a) disruption of the electron transfer connection to the plastoquinone pool, or decrease in the pool size; (b) loss of excitation energy transfer efficiency in the second light period; (c) impairment of the O₂ evolution appratus, as shown by comparison of the efficiency of DCP and H₂O as electron donors.

These conclusions are based on the use of a previously developed method of measurement and analysis of data (Cahen et al. 1976 Plant Physiol 58: 257-267).