Effect of inhibitors on ammonium assimilation in Chlorella sorokiniana in light and darkness |
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Authors: | Carmelo Rigano Vittoria Di Martino Rigano Vincenza Vona Sergio Esposito Catello Di Martino |
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Institution: | Dipto Biologia Vegetale. Univ. di Napoli, Federico II, Via Foria 223, 1-80139 Napoli, Italy.;Dipto di Scienze Animali, Vegetali e dell'Ambiente, Univ. del Molise, I-86100 Campobasso, Italy. |
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Abstract: | In N-sufficient cells of Chlorella sorokiniana Shihira and Krauss strain 211/8K (CCAP of Cambridge University), assimilation of ammonium was strictly dependent on light and CO2, and was severely inhibited by 100 μ M atrazine or 10 μ M 3-(3,4-dichlorophenyl)-1, l-dimethylurea (DCMU). In N-limited cells, assimilation of NH4+ took place at similar rates in both light and darkness, which were 1.6-fold higher than the rate of light-dependent assimilation by N-sufficient cells. Assimilation by N-limited cells was inhibited by l -methionine- dl -sulfoximine (MSX), but not by atrazine or DCMU. The rate of photosynthetic O2 evolution was 2.9±0.9 mmol ml−1 packed cell volume (PCV) h−1 in N-sufficient cells, and 0.64±0.12 mmol ml−1 PCV h−1 in N-limited cells. In the latter resupply of ammonium resulted in a rapid activation by 22%;, followed by a time-dependent increase of the photosynthetic O2 evolution, which after 12 h reached the same rate as in N-sufficient cells. Respiratory consumption of oxygen in darkness in N-sufficient and N-limited cells was 0.10±0.03 and 0.11±0.02 mmol ml−1 PCV h−1, respectively. Addition of ammonium was without effect on respiration of N-sufficient cells, but resulted in a 4-fold stimulation of respiration of N-limited cells. Such stimulation took place also in cells treated with DCMU, atrazine, or MSX, and it was also promoted by methylammonium. The stimulation of respiration lasted for several hours. |
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Keywords: | Algal photosynthesis algal respiration ammonium assimilation atrazine Chlorella sorokiniana 3(3 4-dichloro-phenyl)-l l-dimethylurea methionine-dl-sulfoximine |
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