PLANT PHYSIOLOGY , Vol 113, Issue 1 137-147, Copyright © 1997 by American Society of Plant Biologists
Conversion of Chlorophyll b to Chlorophyll a and the Assembly of Chlorophyll with Apoproteins by Isolated Chloroplasts
T. Ohtsuka, H. Ito and A. Tanaka
Department of Botany, Faculty of Science, Kyoto University, Kyoto 606-01 Japan
The photosynthetic apparatus is reorganized during acclimation to various
light environments. During adaptation of plants grown under a low-light to
high-light environment, the light-harvesting chlorophyll a/b-protein
complexes decompose concomitantly with an increase in the core complex of
photosystem II. To study the mechanisms for reorganization of photosystems,
the assembly of chlorophyll with apoproteins was investigated using
isolated chloroplasts. When [14C]chlorophyllide b was incubated with
chloroplasts in the presence of phytyl pyrophosphate, it was esterified and
some of the [14C]chlorophyll b was converted to [14C]chlorophyll a via
7-hydroxymethyl chlorophyll. [14C]Chlorophyll a and b were incorporated
into chlorophyll-protein complexes. Light-harvesting chlorophyll
a/b-protein complexes of PSII had a lower [14C]chlorophyll a to
[14C]chlorophyll b ratio than P700-chlorophyll a-protein complexes,
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 become assembled with any
apoproteins. These results indicate that chlorophyll b is released from
light-harvesting chlorophyll a/b-protein complexes of photosystem II and
converted to chlorophyll a via 7-hydroxymethyl chlorophyll in the lipid
bilayer and is then used for the formation of core complexes of
photosystems. These mechanisms provide the fast, fine regulation of the
photosynthetic apparatus during construction of photosystems.
