Changes in the abundance of individual apoproteins of light-harvesting chlorophyll [formula omitted] complexes of Photosystem I and II with growth irradiance in the marine chlorophyte Dunaliella tertiolecta

Abstract

The marine chlorophyte Dunaliella tertiolecta responds to increased growth irradiance (in the range 70–1900 μmol quanta·m −2·s −1) by decreasing its cellular content of reaction centers I and II by as much as 75% (Sukenik, A., Bennett, J. and Falkowski, P.G. (1987) Biochim. Biophys. Acta 891, 205–215). We have used Western blot techniques and antibodies raised against homologous pea proteins to examine changes in the concentration of the corresponding light-harvesting antenna complexes, LHC I and LHC II. Three LHC I apoproteins (22, 27.5 and 32 kDa) and four LHC II apoproteins (24.5, 28.5, 30 and 31 kDa) were detected. With increasing growth irradiance, the 22 and 27.5 kDa LHC I apoproteins and the 30 and 31 kDa LHC II apoproteins declined in parallel with RC I and RC II. In contrast, the 32 kDa LHC I apoprotein remained equally abundant per cell at all irradiances and the 28.5 kDa II apoprotein declined by only 30%. The fact that purified LHC II extracted from high-light cells (1200 μmol quanta·m −2·s −1) contained a lower chlorophyll (Chl) b content than LHC II purified from low-light cells (70 μmol quanta·m −2·s −1) suggests that the LHC II apoproteins differ in their capacity to bind Chl b. We conclude that photo-adaptive changes in pigment composition in D. tertiolecta are brought about not only by changes in the total abundance of LHC I and LHC II, but also by differential accumulation of individual LHC I and LHC II apoproteins. A simple procedure for detecting irradiance-dependent changes in the light-harvesting apparatus of other green algae is presented.