PHOTOSYNTHETIC PIGMENT ORGANIZATION IN DIATOMS (BACILLARIOPHYCEAE)¹

Abstract

The isolation and characterization of six pigment‐protein complexes from five diatom species (Phaeodactylum tricornutum Bohlin, Chaetoceros gracilis Schutt, Nitzschia sp. Mono Lake, Nitzschia laevis Hust. and Thalassiosira pseudonana (Hust.) Hasle and Heimdal) was accomplished by membrane dissociation with digitonin followed by gel electrophoresis. Six analogous complexes obtained from all species were correlated in spectral characteristics and relative mass with complexes from higher plants obtained by the same procedure. The largest of these complexes, comprising about 15% of the total Chl a, contained reaction centers of Photosystem I (PSI) and antenna pigments (LHC1).Some PSI complexes also separated from LHC1 in the gel. For the first time in diatoms, a Photosystem II complex was isolated and identified from its position in the gels, absorption and fluorescence spectra, lack of P700, and enrichment carotene. Three antenna pigment‐protein complexes in addition to LHC1 occurred in varying proportion under different experimental conditions but in sum, they accounted for 70% of the total Chl a. All three bands were highly enriched in Chl c and fucoxanthin, although the ratio of Chl c/ xanthophyll decreased between the slowest migrating LHC2 and fastest moving LHC4 LHC3 contained the highest proportio of pigment‐protein and was composed primarily of polypeptides of about 18,000 D. Essentially all α‐ and β‐carotene was bound to the reaction center complexes. The Nitzschia from Mono Lake differed from the other species in that PSI complexes could not be readily dissociated from its membrane by digitonin treatment, a characteristic which may reflect a different chloroplast membrane structure in this alga.

The Regulation of Carbon and Nutrient Assimilation in Diatoms is Significantly Different from Green Algae

“…Instead, thylakoids run the whole length of the plastids in bands of three thylakoids each and no segregation of PSs could be detected so far. In addition, no special PS I or PS II antenna could be found (Berkaloff et al 1990;Brown 1988;Owens and Wold 1986). Despite these differences in the organisation of thylakoid assembly, light-harvesting systems in diatoms are also membrane intrinsic proteins.…”

Bioenergetic changes in the microalgal photosynthetic apparatus by extremely high CO2 concentrations induce an intense biomass production

“…The impact of elevated carbon dioxide concentrations on different cyanobacteria was a decrement of quantum requirement and a reduction of the variable fluorescence in the presence of DCMU (electron transport inhibitor) compared with the cultures grown under low carbon dioxide (Bhatti et al 2002, Miyachi et al 1996). Furthermore, the function and the structure of the photosynthetic apparatus of many algal species resemble those of higher plants (Brown 1988, Plumley and Schmidt 1984, Plumley et al 1993). Microalgae exhibit much higher growth rates than higher plants, can utilize higher carbon dioxide concentrations and can grow under conditions unsuitable for higher plants (Brown and Zeiler 1993).…”

COMPARATIVE EFFECTS OF LIGHT ON PIGMENTS OF TWO STRAINS OF EMILIANIA HUXLEYI (HAPTOPHYTA)1

“…This further supports the hypothesis that the biosynthetic pathways of 19 Hex and Fuco are linked, but also that the tight regulation of the biosynthesis/metabolism pathways relates to the light‐harvesting protein–pigment complexes of PS I and II (Sukenik et al 1988). Brown (1988) reported that chl c is only associated with the LHC in diatoms while chl a is localized both in the reaction centers I and II and the LHC. Thus, variability of the chl c : a ratio may indicate changes in the ratio of light harvesting to reaction center complexes.…”