Short-term 14C incorporation in Skeletonema costatum (Greville) Cleve (Bacillariophyceae) as a function of light regime

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Abstract
Photosynthetic carbon metabolism of diatoms is difficult to understand, and experiments conducted by different authors lead to contradictory conclusions. The pattern of carbon fixation was studied in Skeletonema costatum cultured under three different light regimes (continuous light CL; 12 h light/12 h dark cycles: 12 h/12 h; 2 h light/2 h dark cycles: 2 h/2 h). The short-term incorporation of NaH14CO3 (10–60 s) into photosynthetic products showed that 3-phosphoglycerate was the initial product of photosynthetic CO2 fixation. Although this diatom presented a predominant C-3 pathway, 14C incorporation also occurred by β carboxylation (C-4 metabolism). Incorporation into metabolites off β carboxylation was constant whatever the light regime, whereas the importance of the C-3 pathway varied. It is noteworthy that with aging of the culture 14C incorporation decreased and that under continuous light, there was less fixation in Skeletonema costatum by the C-3 pathway. We found that continuous light is ...