Abstract
N‐sufficient cells of Chlorella sorokiniana Shihira and Krauss, strain 211/8k, absorbed NH4+ under light plus CO2 conditions, when growth occurred, but not in darkness or in the absence of CO2, when growth was inhibited. N‐sufficient cells subjected to conditions of N‐starvation for a 24‐h period showed a marked loss of photosynthetic activity. Upon supply of NH4+, N‐starved cells sufflated with CO2 air exhibited a time‐dependent recovery of photosynthetic activity, both when suspended in light and in darkness. By contrast, growth only occurred in cells suspended in light. N‐starved cells absorbed NH4+ in darkness, but at a lower rate than in light. All of these data suggest that dark NH4+ uptake is driven by N assimilation to recover from N‐starvation and that the light‐dependent NH4+ uptake is driven by growth, being then influenced by conditions that affect recovery or growth. Unlike CO2 conditions, in a CO2‐free atmosphere, absorption of NH4+ by N‐starved cells occurred at a higher rate in darkness than in light. Accordingly, resumption of photosynthetic potential after NH4+ supply occurred in darkened cells, but not in illuminated cells. Respiratory activity of N‐starved cells was enhanced up to 3‐fold by NH4+ and 2‐fold by methylammonium, with different patterns, suggesting that respiratory enzymes were affected by N‐metabolism, especially through short‐term control mechanisms triggered by the expenditure of metabolic energy involved in N‐metabolism.
Published Version
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