Photosynthetic pigments and pigment-proteins in natural populations of Antarctic sea-ice diatoms

Pigment analyses of natural populations of sea-ice diatoms in Antarctica showed a range of chlorophyll a : c molar ratios of 1.85–3.83 and carotenoid (fucoxanthin): chlorophyll a molar ratios of 1.52–2.57. To understand the structural organization of pigments in these low light-adapted populations, the photosynthetic apparatus of a monospecific natural population of the Antarctic sea ice diatom, Nitzschia stellata Manguin (Bacillariophyta), was investigated. Three chlorophyll-protein complexes were isolated from the thylakoid membranes of this diatom. Spectral and pigment analyses revealed that, while all three complexes possessed chlorophyll a and fucoxanthin, chlorophyll c was found only in Complexes I and II. Fifty-nine per cent of the chlorophyll c was found in Complex I, which possessed a chlorophyll a: chlorophyll c: fucoxanthin ratio of 1 : 2: 1, a ratio enriched in accessory pigments compared to whole cell ratios. Complex III contained fucoxanthin and 53% of the total chlorophyll a; this complex contained polypeptides in the 18.5 kDa range. These results are in contrast with those previously reported for studies of temperate diatoms. This is the first investigation of the pigment-protein composition of a natural (field) population of diatoms.