Characteristics of light-induced 515-nm absorbance change in spinach chloroplasts at lower temperatures II. Relationship between 515-nm absorbance change and rapid H+uptake in chloroplasts after a short flash illumination

摘要

The absorbance change at 515 nm induced by a short (7.6μsec) light flash in spinach chloroplasts was studied at sub-room temperatures in relation to rapid H+uptake into chloroplasts.Lowering of temperature caused a marked decrease in the rate of recovery of 515-nm absorbance change after a flash illumination. Initial rate of rapid H+uptake, measured with absorbance change of bromcresol purple (BCP), was also reduced at lower temperatures, in a parallel fashion. Half-recovery time of the absorbance change at 515 nm and rise-time of the pH-indicating absorbance increase of BCP coincided well at each temperature studied. Values of the calculated activation energy for these two processes were almost the same.The parallelism between the 515-nm absorbance change and the rapid H+uptake after a single flash illumination was also observed when the electric field decay and/or H+translocation were accelerated by ionophorous antibiotics, carbonylcyanidem-chlorophenylhydrazone or phenazine methosulfate. From these results, it is suggested that the rapid H+uptake into chloroplast is chemically coupled to electron transfer and at the same time diffusion- (or transport-) controlled. Membrane potential, reflected in the 515-nm absorbance change is dissipated with the rapid H+influx. A model for the electron-transfer-coupled H+translocation involving a plastosemiquinone loop is presented. Dissipation of the illumination-formed inside-positive membrane potential by the influx of H+is explained by the model