Ageing of chloroplasts in vitro II. Changes in absorption spectra and the DCPIP Hill reaction

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Changes in absorption characteristics and in Hill activity were studied during ageing of isolated chloroplasts in the dark and light. Ageing of chloroplasts brings about significant reduction in the peak absorption in the blue and red bands and results in a blue shift in the red band. Incubation of chloroplasts in the dark prevented the early appearance of a light-induced blue shift at pH 7 and pH 8 but not at pH 6 of the storage media. Addition of BSA or DTT to chloroplast suspensions of pH 6 and pH 7 significantly delayed the blue shift both in the light and dark, but the chemicals had no effect at pH 8. Ageing-induced loss in DCPIP reduction is restored considerably by the addition of exogenous electron donors such as DPC or Mn^<2+> which suggests loss of the oxygen evolution system. Mn^<2+> loses its ability to donate electrons for DCPIP photoreduction during ageing faster than DPC. This indicates that there are two sites between water and the PS II reaction centre for the entry of electrons from these two donors and that ageing causes sequential loss of these sites. The loss in DPC supported DCPIP photoreduction coincides, in time, with the ageing-induced blue shift of the red absorption band and thus suggests structure and function relations of the plastid membrane.
日本植物生理学会の論文