Discrimination and characterization of photosystem I- and photosystem II-induced 515-nm absorbance change in chloroplasts I. Dissipation of electric field and related processes

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Abstract
Distinctive characteristics of the photosystem I-induced 515-nm absorbance change and the photosystem II-induced change were analyzed in spinach chloroplasts in the absence of added salt. Two types of changes were distinguished by 3-(3,4-dichloro-phenyl)-1,1-dimethylurea (DCMU), carbonylcyanide m-chlorophenylhydrazone (CCCP) and illumination with red or far-red light. Half-recovery time of the photosystem I-induced absorbance change was shorter than that of over-all absorbance change and was insensitive to a low concentration (<0.50 μM) of CCCP. In the presence of DCMU, the 515-nm absorbance change decayed in parallel with the rapid protonation of reduced 2,6-dichloroindophenol (DCIP) or methyl viologen. This indicates that the photosystem I-induced local field is dissipated in the electron transfer from photosystem I to an electron acceptor. Thus the mechanism in dissipation of electric field formed by photosystem I is different from that induced by photosystem II where rapid protonation of plastosemiquinone anion may be directly involved in field dissipation (Yamamoto, Y. and M. Nishimura: Plant & Cell Physiol. 18: 293–301 (1977)).