Conversion of Chlorophyll b to Chlorophyll a and the Assembly of Chlorophyll with Apoproteins

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Photosynthetic apparatus is reorganized during acclimation to various light environment. It is known that during adaptation of low light grown plants to high light, light-harvesting chlorophyll a/b-protein complexes decomposes concomitant increase in core complexes of photosystem II.In order to study the mechanisms for reorganization of photosystems, assembly of chlorophyll with apoproteins was investigated by isolated chloroplasts. When 14C-chlorophyllide b was incubated with chloroplasts in the presence of phytylpyrophosphate, 14C-chlorophyllide b was esterified and some of the 14C-chlorophyll b was converted to 14C-chlorophyll a via 7-hydroxymethyl chlorophyll. These 14C-chlorophyll a and b were incorporated into chlorophyll-protein complexes. Light-harvesting chlorophyll a/b-protein complexes of photosystem II had lower 14C-chlorophyll a/14C-chlorophyll b ratio and P700-chlorophyll a-protein complexes had higher ratio, indicating the specific binding of chlorophyll to apoproteins in our systems. 7-Hydroxymethyl chlorophyll, an intermediate molecule from chlorophyll b to chlorophyll a, did not assemble to any apoproteins. These results indicate that chlorophyll b releases from light-harvesting chlorophyll a/b-protein complexes of photosystem II and converted to chlorophyll b via 7-hydroxymethyl chlorophyll in lipid bilayr and them used for the formation of core complexes of photosystems.