Effects of light quality, CO2 tensions and NO 3 (+-) concentrations on the inorganic nitrogen metabolism of Chlamydomonas reinhardii.
The blue light dependent utilization of nitrate by green algae under common air and high irradiances, besides its assimilatory nature, is associated with the release of NO2 (-) and NH4 (+) to the culture medium. If the CO2 content of the sparging air was increased up to 2%, previously excreted NO2 (-) and NH4 (+) were rapidly assimilated. When under air and high irradiances the cell density in the culture reached values corresponding to 25 μg Ch 1.ml(-1), no further growth was observed and the highest values of NO3 (-) consumption and NO2 (-) and NH4 (+) release were attained. Besides low CO2 tensions, increasing NO3 (-) concentrations in the medium stimulated the release of NO3 (-) and NH4 (+). Under CO2-free air the consumption of NO3 (-) and the release of NO2 (-) and NH4 (+) on a total N bases were almost stoichiometric and their rates saturated at much lower irradiances than under air. Under CO2-free air high rates of NO2 (-) release were only observed under the blue radiations that were effectively absorbed by photosynthetically active pigments, i.e. 460 nm, but not under 404 and 630 nm radiations. However, the simultaneous illumination of the cells with 404 and 630 nm monochromatic light showed a remarkable synergistic effect on NO2 (-) release.The results are discussed in terms of the close relationship between C and N metabolism, the photosynthetic reducing power required to convert NO inf3 (sup±) -N into R - NH2-N and the blue light activation of nitrate reductase.
Instituto de Biologia Cellular, CSIC, Velazquez, 144, Madrid-6, Spain.
M P
MP
Azuara
P J
PJ
Aparicio