Journal Article

Irradiance-Dependent Changes in the Size and Composition of the Chlorophyll <i>a-b</i> Light-Harvesting Complex in the Green Alga <i>Dunaliella salina</i>

Ayumi Tanaka and Anastasios Melis

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 38, issue 1, pages 17-24
Published in print January 1997 | ISSN: 0032-0781
Published online January 1997 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/oxfordjournals.pcp.a029080
Irradiance-Dependent Changes in the Size and Composition of the Chlorophyll a-b Light-Harvesting Complex in the Green Alga Dunaliella salina

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Irradiance-dependent adjustments in the size and composition of the Chi a-b light-harvesting protein complex (LHC-II) were investigated in the green alga Dunaliella salina. Cells grown under low irradiance (100 μmol photons m−2s−1) had a low Chl a/Chl b ratio, and an abundance of cellular Chl and LHC-II apoproteins compared to cells grown under high light intensity (2,200 μmol photons m−2s−1). In low-light grown cells, four apoproteins of the LHC-II migrating to 32, 31, 30 and 28.5 kDa were termed according to their apparent molecular mass as LHC-II-1, LHC-II-2, LHC-II-3 and LHC-II-4, respectively. In thylakoid membranes from high-light grown cells, LHC-II-1 was practically missing and LHC-II-2 was greatly depleted. On a cell basis, the steady-state amount of total LHC-II apoprotein in high-light grown cells, measured either from the intensity of protein staining by Coomassie brilliant blue or from Western blotting, was 5–7% of that in low-light. In vivo rates of apoprotein biosynthesis were measured from the time course of [35S]sulfate incorporation into LHC-II. On a cell basis, the rate of biosynthesis in highlight grown cells was about 20% of that in low-light grown cells. Thus, in high-light grown cells, the rate of LHC-II apoprotein biosynthesis was ˜3 times greater than the steady-state amounts of LHC-II present in thylakoids. The results suggest discrete irradiance-dependent transcriptional and posttranslational regulation steps that define the amount and composition of the LHC-II in chloroplasts.

Keywords: Assembly; Light-harvesting complex; Protein composition; Photosynthetic unit; Thylakoid membrane; Dunaliella salina

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Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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