523 research outputs found
Nitrate and ammonium assimilation in algal cell-suspensions and related pH variations in the external medium, monitored by electrodes
No full textNitrate and ammonium utilization in cell suspension of the acidophilic thermophilic non-vacuolate alga Cyanidium caldarium and the related pH variations in the external medium, were measured using ion specific electrodes. Nitrate absorption and pH variations were also monitored. The acidophilic C. caldarium allowed experimentation under acidic conditions where CO2 exchange did not affect pH measurements. Both ammonium and nitrate assimilation occured in dark and light conditions; however, the rate of assimilation was higher in the light than in the dark. The presence of oxygen was an absolute requirement. It is suggested that the uptake of both nitrate and ammonium are mediated by active mechanisms dependent on the energy charge of the cell. The assimilation of nitrate and ammonium was accompanied by an increase and a decrease, respectively, of the external medium pH. Under steady-state conditions, for each equivalent of ammonium incorporated there were 0.8-1 equiv. of protons released into the external medium and for each equivalent of nitrate absorbed there were 1-1.2 equiv. of protons absorbed from the external medium
Nitrate reductase and glutamine synthetase activities, nitrate and ammonia assimilation, in the unicellular alga Cyanidium caldarium
No full textNitrogen-limited continuous cultures of Cyanidium caldarium contained induced levels of glutamine synthetase and nitrate reductase when either nitrate or ammonia was the sole nitrogen source. Nitrate reductase occurred in a catalytically active form. In the presence of excess ammonia, glutamine synthetase and nitrate reductase were repressed, the latter enzyme completely. In the presence of excess nitrate, intermediate levels of glutamine synthetase activity occurred. Nitrate reductase was derepressed but occurred up to 60% in a catalytically inactive form. Cell suspensions of C. caldarium from nitrate- or ammonialimited cultures assimilated either ammonia or nitrate immediately when provided with these nutrients. In these types of cells, as well as in cells grown with excess nitrate, the rate of ammonia assimilation was 2.5-fold higher than the rate of nitrate assimilation. It is proposed that the reduced rate at which nitrate was assimilated as compared to ammonia might be due to regulatory mechanisms which operate at the level of nitrate reductase activity. © 1981 Springer-Verlag
Nitrogen assimilation in a thermophilic acidophilic alga
No full textThermophilic eukaryotic algae are rare in acid hot environments in nature. The sole photosynthetic organisms living in thermal alkaline environments are almost exclusively cyanobacteria. Among algae, only the members of the class Cyanidiophyceae [including the families Cyanidiaceae and Galdieriaceae (Merola et al. 1981)] were found to live in thermal acidic habitats up to 57 °C (Doemel and Brock 1970). The family Cyanidiaceae includes the alga Cyanidium caldarium. For a larger spec trum on these algae, see chapters by Seckbach, Ott and by Sentsova in this volum
Nitrate and ammonium assimilation in algal cell-suspensions and related pH variations in the external medium, monitored by electrodes
No full textNitrate and ammonium utilization in cell suspension of the acidophilic thermophilic non-vacuolate alga Cyanidium caldarium and the related pH variations in the external medium, were measured using ion specific electrodes. Nitrate absorption and pH variations were also monitored. The acidophilic C. caldarium allowed experimentation under acidic conditions where CO2 exchange did not affect pH measurements. Both ammonium and nitrate assimilation occured in dark and light conditions; however, the rate of assimilation was higher in the light than in the dark. The presence of oxygen was an absolute requirement. It is suggested that the uptake of both nitrate and ammonium are mediated by active mechanisms dependent on the energy charge of the cell. The assimilation of nitrate and ammonium was accompanied by an increase and a decrease, respectively, of the external medium pH. Under steady-state conditions, for each equivalent of ammonium incorporated there were 0.8-1 equiv. of protons released into the external medium and for each equivalent of nitrate absorbed there were 1-1.2 equiv. of protons absorbed from the external medium
Effect of darkness and CO2 starvation on NH4+ and NO3- assimilation in the unicellular alga Cyanidium caldarium.
No full textTemperature responses of growth, photosynthesis, respiration and NADH:nitrate reductase in the cryophilic algae Koliella antarctica and "Chlorella" saccarophila, and in the mesophilic green alga Chlorella sorokiniana
No full text• Temperature effects on growth, photosynthesis, respiration and nitrate reductase (NR) were studied in the cryophilic algae Koliella antarctica and ‘Chlorella’ saccharophila , and in the mesophilic Chlorella sorokiniana .
• Growth rate was measured as increase in optical density. Photosynthesis at saturating light and respiration in darkness were measured as O2 exchange. NADH : NR was assayed in crude extracts.
• The two cryophilic algae grew below 15 °C, and C. sorokiniana above 20 °C. Photosynthetic and respiration rates of K. antarctica and ‘C .’ saccharophila were elevated at 5 °C, and peaked at 30 °C. Arrhenius plots from 5 to 25 °C were linear in K. antarctica , whereas in ‘C .’ saccharophila and C. sorokiniana they exhibited breaks at 15 and 20 °C, respectively. Values for activation energy (Ea) and the factor by which the rate increases with raising the temperature 10 °C (Q10) differed. Nitrate reductase had its optimum at 25 °C in cryophilic algae and at 35 °C in C. sorokiniana .
• We conclude that growth of cryophilic algae at low temperature is favoured by elevated photosynthesis and respiration rates, but that it could be limited by a high respiration : photosynthesis ratio
Effect of inhibitors on ammonium assimilation in Chlorella sorokiniana in light and darkness.
No full textEffects of sulfur nutrition on carbon metabolism and nitrogen assimilation in Chlorella sorokiniana
No full textMontpellier – Franc
Effect of inhibitors on ammonium assimilation in Chlorella sorokiniana in light and darkness.
No full textLight-dependent decline of NH4+ assimilation under CO2 deprivation in N-limited Chlorella sorokiniana (Chlorophyceae).
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