in dark-grown pine seedlings

Green plastida prepared from seedlings of Pinus silotstris harvested after three weeks of growth in the dark, without exposure to light, catalyzed photoreductions of methyl viologen and nicotinamide-adenine dinucleotide phosphate, and cyclic photophosphory-lation with AT-methylphenazonium methosulfate, but could not catalyze the photoreduc-tion of 2,4-dichlorophenol indophenol in the absence and presence of diphenylcarbazide. In dark-grown seedlings of Pinus silvestris, functional photosystem I developed with no exposure to light, but no photosystem II activity was observed. Dark-grown seedlings of angiosperms lack chlorophyll, while dark-grown coniferous seedlings contain chlorophyll (7). This is due to the fact that the transformation of protochlorophyllide to chlorophyllide in the biosynthetdc process of chlorophyll proceeds as a photo-reaction in the former seedlings and as a dark-reaction in the latter. Therefore, in dark-grown seedlings of angiosperms, photo-synthetic activities can not be developed without illumination. Exposing etiolated leaves of dark-grown seedlings to light is the essential factor for the formation of chlorophyll and the functional differentiation of photosystems I and II (2-5). Recendy, we confirmed quantitatively that dark-grown seedlings of Pinus (P. taeda, P. tkunbergii, P. densithunbergii, P. densiflora and P. silvestris), Cryptomcria japonica, Picea excelsa and Chamaecyparis obtusa contain chlorophylls a and b. T h e ratio of chlorophyll a to b in these seedlings was from 2.2 to 4.0 (unpublished data). These ratios are near the values for mature leaves. This suggests the possibility that photosynthetic activities develop in plastids of dark-grown coniferous seedlings, without exposure to light. We succeeded in isolating photoactive chloroplasts from mature leaves of Pinus tkunbergii two years ago (6, 7). This prompted us to investigate the functional development of plastids in dark-grown pine seedlings. The present paper deals with photoreactions associated with photosystem