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

Abstract

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 (CP1) and Chl a-protein complex of the PS II core (CPa) increased, with a concomitant decrease in the light-harvesting Chl 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 CP1 and CPa increased while those of Chi b decreased during the dark incubation. Since Chl is not synthesized in the dark, Chl must be released from LHCII and re-incorporated into CP1 and CPa. The amounts of apoproteins of CP1 and 43 kDa protein (one of the apoproteins of CPa) increased during the dark incubation, and the increase could be inhibited by chloramphenicol (CAP). CP1 did not increase in the dark when tissues were incubated with CAP which inhibited the synthesis of apoproteins of CP1, indicating that CP formation by Chl redistribution needs newly synthesized apoproteins. The decrease in LHCII apoproteins during dark incubation was inhibited by CAP probably because Chl was not removed from LHCII by apoproteins of CP1 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, Chl b and LHCII apoproteins accumulated with the disappearance of 43 kDa protein; Chl of 43 kDa protein may be utilized for LHCII formation. We concluded that Chl molecules once bound with their apoproteins are redistributed among the apoproteins.