Formation of Chlorophyll-Protein Complexes in Greening Cucumber Cotyledons in Light and then in Darkness

The changes in chlorophyll-protein complexes (CPs) in cucumber cotyledons during illumination and subsequent dark incubation were studied by SDS-polyacrylamide gel electrophoresis. When etiolated cucumber seedlings were illuminated, chlorophyll was synthesized and CPs were formed. In the early phase of greening (6 h of illumination), light-harvesting chlorophyll a/b-protein complex (LHCP) was the main GP. As the greening proceeded, P700 chlorophyll a-protein complex (CP1) accumulated. When 6-h illuminated seedlings were transferred to darkness, CP1 accumulated concomitantly with a decrease in LHCP without new chlorophyll synthesis. The changes in the amounts of CPs in the dark became smaller with the progress of greening and were not observed after 72 h of illumination. These changes were confirmed by examining the chlorophyll/P700 ratio and the low temperature absorption spectrum of cotyledons. These results suggest that in the early phase of greening, CPs were unstable and their chlorophyll molecules easily exchanged with those of other kinds of CPs.