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Abstract

Studies on protein, carbohydrates and lipids synthesis were carried out to test the effects of short and long exposure times to various photon flux densities (PFD) (ranging from 0-3000 μmol. m ⁻².s ⁻¹) on the photosynthate partitioning in a unicellular freshwater phytoplanktonic diatom, Nitzschia palea. Reduced PFD caused increased relative incorporation of ¹⁴C into polysaccharide and protein metabolites and decreased incorporation of ¹⁴C into lipids metabolites. The percent of ¹⁴C in polysaccharide was lowest of all the fractions studied (5-18%). The Low Mol. Wt.-metabolies (LMW) fraction did not change much at higher PFD and longer incubation periods. The relative ¹⁴C incorporated into the lipid fraction increased as PFD increased and this effect is more prominent at longer incubation periods. At higher PFD and longer incubation periods as much as 65% of ¹⁴C-bicarbonate was incorporated into the lipid fraction. Incorporation into protein and polysaccharide was the reverse of the pattern found for in lipids. It is clear from this study that Nitzschia palea (Phytoplanktonic diatom) when incubated at high PFD show enhanced relative rate of lipid and low mol. wt.-metabolies synthesis at the cost of polysaccharide and protein. Therefore, high PFD induced lipid synthesis whereas low PFD enhanced protein and polysaccharide metabolism. This study shows that the effects of PFD and duration of exposure are important in modifying the flow of carbon into major end products of photosynthesis. This means that the physiological response of a population of a species of algae incubated over a longer time period and or at higher PFD differes from same popualtion of a species incubated for shorter time period and or at lower PFD.