Formation of Chlorophyll-Protein Complexes during Greening. 2. Redistribution of Chlorophyll among Apoproteins

The formation of Chl-protein complexes (CPs) in cucumber cotyledons during a dark period after a brief illumination was studied. SDS-PAGE analysis showed that the P700-Chl a-protein complex (CPl) and Chi a-protein complex of the PS II core (CPa) increased, with a concomitant decrease in the light-harvesting Chi a/6-protein complex of PS II (LHCII), during 24-h dark incubation of cotyledons after 6h of continuous illumination. In agreement with these results, curve analysis revealed that spectral components characteristic of CPl and CPa increased while those of Chi b decreased during the dark incubation. Since Chi is not synthesized in the dark, Chi must be released from LHCII and re-incorporated into CPl and CPa. The amounts of apoproteins of CPl and 43 kDa protein (one of the apoproteins of CPa) increased during the dark incubation, and the increase could be inhibited by chloramphenicol (CAP). CPl did not increase in the dark when tissues were incubated with CAP which inhibited the synthesis of apoproteins of CPl , indicating that CP formation by Chi redistribution needs newly synthesized apoproteins. The decrease in LHCII apoproteins during dark incubation was inhibited by CAP probably because Chi was not removed from LHCII by apoproteins of CPl and CPa, whose synthesis was blocked by the presence of CAP. When intermittently-illuminated cotyledons containing a little LHCII were incubated with CaCl2 in the dark, Chi b and LHCII apoproteins accumulated with the disappearance of 43 kDa protein; Chi of 43 kDa protein may be utilized for LHCII formation. We concluded that Chi molecules once bound with their apoproteins are redistributed among the apoproteins.