Hill activity (oxygen evolution with ferricyanide as the electron acceptor), light-induced absorbance changes at liquid nitrogen temperature associated with the primary activity of photosystem II, and fluorescence yield changes at both low temperature and room temperature were measured with lyophilized spinach chloroplasts before and after extraction with hexane and reconstitution with p-carotene and plastoquinone A. Extraction eliminated the Hill activity, and both 8-carotene and plastoquinone A were required for maximal restoration of activity to the reconstituted chloroplasts.Extraction also eliminated the light-induced absorbance changes at -196 C due to the photoreduction of C-550 and photooxidation of cytochrome b5m, and reconstitution with #-carotene and plastoquinone A restored the low temperature photoreactions. However, only 8-carotene was essential for the restoration of the photoreactions. Cytochrome bz9 was modified, as a result of the extraction, to a lower redox potential, autooxidizable form and remained as such after reconstitution with ,8-carotene. The 8-carotene-restored chloroplasts showed the photoreduction of C-550 but not the photooxidation of cytochrome bwg because the cytochrome was already oxidized. When ,8-carotene-reconstituted chloroplasts were suspended in buffer containing ascorbate prior to freezing, the cytochrome b59 was reduced and could be photooxidized by irradiation at low temperature. After reconstitution with 8-carotene plus plastoquinone A the cytochrome bss9 was partially restored to its original high potential form and was in the reduced state so that both the photoreduction of C-550 and the photooxidation of cytochrome b659 occurred on irradiation of the p-carotene plus plastoquinone A-reconstituted chloroplasts. Reconstitution with plastoquinone A alone had essentially no effect on restoring the photoreactions.The fluorescence yield of dark-adapted lyophilized chloroplasts at -196 C showed an irreversible increase of about 2.5-fold during irradiation. After extraction the fluorescence yield of the chloroplasts was high (at the maximal light-induced level of the lyophilized control chloroplasts) and showed very little change in the light. Reconstitution with ,-carotene alone restored some fluorescence quenching which was relieved by irradiation at low temperature. Reconstitution with plastoquinone A alone restored a high degree of quenching, but this quenching was not relieved by light at low temperature. Fluorescence emission spectra at -196 C showed that the fluorescence of variable yield in the lyophilized and 8-carotene-reconstituted chloroplasts involved only the 680 and 695 nm emission bands but not the larger 730 nm emission band, whereas the irreversible quenching in plastoquinone A-reconstituted chloroplasts involved all wavelengths of emission. Extraction of the chloro-' Present address: Biological Laboratory, College of General Education, Kyushu University, Ropponmatsu, Fukuoka, Japan.'To whom reprint requests should be addressed.plasts also eliminat...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.