Nitric oxide generation upon growth of Antarctic Chlorella sp cells

The aim of this work was to characterize nitric oxide (NO) generation during the growth of Chlorella sp. cells. The profile of NO production was compared with that observed in Chlorella from temperate climate and Antarctic Chlamydomonas sp. A distinctive electron paramagnetic resonance (EPR) signal for the adduct MGD-Fe-NO was detected in the Antarctic Chlorella sp. cells on days 6 and 7 of growth. An assay based upon the time-dependent detection of NO by EPR was developed to assess both nitrate reductase (NR) and NO synthase (NOS)-like activities. A significant increase in both enzymatic activities was observed on day 6 of growth of Antarctic Chlorella sp. cells. However, NOS-like activity proved undetectable on day 10 of growth, while NR activity was observed until day 22 of growth. When the cultures were supplemented with N omega-nitro-L-arginine methyl ester (L-NAME) from day 0 to day 13, no growth was observed. After administration of L-NAME from day 5 to day 12, growth rate at log phase was inhibited from 0.18 +/- 0.02 (control) to 0.11 +/- 0.01 per day. Removal of L-NAME on day 12 increased the growth rate to 0.15 +/- 0.02 per day. Supplementation with S-nitroso-N-acetyl-penicillamine on day 5, in the presence of L-NAME from day 0, restored the growth rate to control values. The same profile of NO generation was observed during the growth of Antarctic Chlamydomonas sp.; however, Chlorella cells from temperate climate did not show any difference in NO generation over the growth period. The data reported here are the first observations, by employing EPR, of NO and the activity of the enzymes responsible for its generation during the growth of Antarctic photosynthetic alga.