Calcium-induced formation of chlorophyll b and light-harvesting chlorophyll a/b-protein complex in cucumber cotyledons in the dark

Dark-grown cucumber seedlings were exposed to intermittent light (2 min light and 98 min dark) and then cotyledons were incubated with 50 mM CaCl₂ in the dark. Chlorophyll (Chl) a was selectively accumulated under intermittent light and Chl b was accumulated during the subsequent dark incubation with CaCl₂. The change in chlorophyll-protein complexes during Chl b accumulation induced by CaCl₂ in the dark was investigated by SDS-polyacrylamide gel electrophoresis. Chlorophyll-protein complex I and free chlorophyll were major chlorophyll-containing bands of the cotyledons intermittently illuminated 10 times. When these cotyledons were incubated with CaCl₂ in the dark, the light-harvesting Chl a/b-protein complex was formed. When the number of intermittent illumination periods was extended to 55, small amounts of Chl b and light-harvesting Chl a/b-protein complex were recognized at the end of intermittent light treatment, and these two pigments were further increased during the subsequent incubation of the cotyledons with CaCl₂ in the dark compared to water controls.