ALLOCATION OF PHOTOASSIMILATED CARBON INTO MAJOR ALGAL METABOLITE FRACTIONS - VARIATION BETWEEN 2 DIATOM SPECIES ISOLATED FROM THE WEDDELL SEA (ANTARCTICA)

Distribution of photoassimilated carbon into major metabolite classes differed between two Antarctic diatom species, Nitzschia curta and a s mall unicellular Chaetoceros sp.. Time course uptake studies (over 54 h) revealed that C-14 allocation appeared to be equilibrated after app roximately 8 h at light saturated photosynthesis. During short term da rk periods (6 h), polysaccharides as well as low-molecular-weight comp ounds were catabolised to sustain protein synthesis in the dark, whils t lipid reserves were not mobilised for this process. Experiments with these two species were conducted at 0 and - 1.5-degrees-C, although n o difference in the distribution of radiolabel was measured between th e two temperatures. It is hypothesised that under near-optimal conditi ons fast growing species are characterised by a high carbon turnover a ssociated with a rapid flow of newly assimilated carbon into polymeric compound classes. On the other hand, slower growing species (such as N. curta) may store a significant amount of surplus carbon in the low- molecular-weight metabolite fraction. Species specific preferences wer e observed when comparing the accumulation of radiolabel into the lipi d pools.