Changes in nitric oxide/hydrogen peroxide content and cell cycle progression: Study with synchronized cultures of green alga Chlamydomonas reinhardtii.

The present study aimed to evaluate the possible relationship between the changes in hydrogen peroxide (HO) and nitric oxide (NO) content and the course of growth and reproductive processes of the cell cycle of Chlamydomonas reinhardtii. The peak of HO observed at the beginning of the cell cycle was found to originate from Fe-SOD and Mn-SOD activity and result from the alternation in the photosynthetic processes caused by the dark-to-light transition of daughter cells. A rapid increase in NO concentration, observed before the light-to-dark cell transition, originated from NR and NIR activity and was followed by a photosynthesis-independent, Mn-SOD-mediated increases in HO production. This HO peak overlapped the beginning of Chlamydomonas cell division, which was indicated by a profile of CYCs and CDKs characteristic of cells' passage through the G1/S and S/M checkpoints. Taken together, our results show that there is a clear relationship between the course of the Chlamydomonas cell cycle and typical changes in the HO/NO ratio, as well as changes in expression and activity of enzymes involved in generation and scavenging of these signaling molecules.