Effects of light quality, CO2 tensions and NO 3 +? concentrations on the inorganic nitrogen metabolism of Chlamydomonas reinhardii

Abstract

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.

Photoregulation of Nitrate Utilization in Green Algae and Higher Plants*

“…We have investigated it and from our data it can be concluded that very low amounts of hydroxylamine inactivate NR and furthermore that the hydroxylamineinactivated NR is susceptible to blue light reactivation. NR extracted from green algae and higher plants in its inactive form is activated by irradiation of the cell-free extracts with blue light (Aparicio et a f . , 1976;Aparicio and Maldonado, 1979;Azuara and Aparicio, 1983;Aryan et al, 1983), CN--, C2H2-and NH20H-inactivated NR are likewise readily reactivated by blue light (Aparicio and Maldonado, 1979;Maurino et al, 1983;this paper). Experiments are in progress to verify the possible in vivo effects of hydroxylamine on the inorganic nitrogen metabolism in green algae.…”

“…Recently we have found that in green algae the utilization of oxidized nitrogen sources is not only assimilatory but also dissimilatory, since these organisms can use oxidized nitrogen anions as electron sinks to unload their excess of reducing power excreting NO; and/or NH: to the culture medium Azuara and Aparicio, 1984;Larsson et al, 1982). In the green algae Chlamydomonas reinhardii these excretions take place not only under high light irradiance and low C 0 2 tensions but also in the dark under anaerobic conditions substituting the evolution of H2 by NH; excretion .…”

Dark induction of nitrate reductase in the halophilic alga Dunaliella salina

“…s- Florencio and Vega 1982;Franco et al 1987Franco et al , 1988. Light has a strong influence on NO~ uptake and the induction of NR in algae (Guerrero et al 1981;Azuara and Aparicio 1983;Solomonson and Barber 1990) and higher plants (Mohr et al 1992;Becker et al 1992). 1A).…”

“…Light, the presence of NO~ and CO/ promote NR synthesis (Herrera et al 1972;Azuara and Aparicio 1983;Larsson et al 1985;Ramazanov et al 1988;Mohr et al 1992). In contrast, darkness or the presence ofNH + represses NR and NIR synthesis (Herrera et al 1972;Guerrero et al 1981 ;Florencio and Vega 1982;Franco et al 1987Franco et al , 1988Mohr et al 1992).…”

Nitrite accumulation by Synechococcus 6301 as a consequence of carbon- or sulfur-deficiency

“…That means that the electron requirement of nitrate assiinilation is about onehalf that of carbon assimilation [3]. Thus, a strict coregulation between these two assimilatory pathways can be expected and extensive work has been done concerning this problem using cyanobacteria [3,4] as well as green algae [5,6] and higher plants [7,81. Moreover the protein composition determines a C/N/S ratio of about 100/17/1. Therefore, besides carbon dioxide and nitrate reduction a balanced sulfate reduction rate has to be guaranteed, a problem which is often neglected in the literature.…”