The aim of this study was to characterize the variation and regulation of photosynthetic carbon metabolism in Cylindrotheca fusiformis during the cell cycle. The cells were synchronized using two cell cycle inhibitors: one for cells grown under light:dark cycles and one for growth in continuous light. We observed that the maximal photosynthetic capacity, PBm and ETRm were lowest just before cell division, when the percentage of cells in G2+M was maximal, and were highest after division, when the percentage of cells in G1 was maximal. These results clearly show that photosynthetic activity is related to the cell cycle. In addition, the role of different oxygen uptake processes was determined using 18O2. We showed that light stimulated oxygen uptake, which increased with irradiance between 0 and 250 wmol photons mvmv2 svmv1. This variation was partly due to an increase of mitochondrial respiration, but mostly to a high Mehler activity. It seems that this increase was due to the Mehler reaction rather than photorespiration, because no increase of oxygen uptake was observed at low DIC (0.1 mM) concentration, which should have stimulated Rubisco oxygenase if there was diffusive CO2 entry. The activity of the Mehler reaction was independent of the cell cycle and explained 50v-v60% of the light stimulated oxygen uptake at irradiances equal to or exceeding the growth irradiance. [KEYWORDS: cell-cycle ; Cylindrotheca fusiformis; diatom; Mehler reaction; mitochondrial respiration; photosynthesis; photorespiration]
Original languageEnglish
JournalEuropean Journal of Phycology
Journal publication date2004

ID: 180903