The physiological significance of light and dark NH 4+ metabolism in Chlorella sorokiniana

• Published in: Phytochemistry (Oxford) Vol. 47; no. 2; pp. 177 - 181
• Main Authors: Di Martino Rigano, Vittoria, Vona, Vincenza, Esposito, Sergio, Carillo, Petronia, Carfagna, Simona, Rigano, Carmelo
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 1998; Elsevier
• Subjects: Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Metabolism; Nitrogen metabolism; Plant physiology and development; algal respiration; NH 4 + assimilation; Chlorophyta; Chlorella sorokiniana; nitrogen metabolism; Assimilation; Light effect; Ammonium; Nutrition; Algae; Light; Nitrogen; Metabolism; Photosynthesis; Respiration; Thallophyta
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/S0031-9422(97)00569-4

N-limited cells of Chlorella sorokiniana Shihira and Krauss 211/8k exhibited rates of respiratory oxygen consumption and photosynthetic oxygen evolution which were 70 and 17%, respectively, of those of N-sufficient cells. N-sufficient cells absorbed NH 4 + in light at a linear rate, and absorption was 100% inhibited by darkness. N-limited cells, by contrast, absorbed NH 4 + at almost similar rates in light and darkness. The rate of uptake in darkness decreased after 20 min, and decreased further after 60 min. In the light, by contrast, it decreased to a constant higher value, which appeared to approximate the sum of the rate of the dark absorption plus the rate of the light-dependent NH 4 + absorption by N-sufficient cells. NH 4 + in darkness did not affect respiration of N-sufficient cells. However, NH 4 + supply to N-limited cells in darkness resulted in a sudden increase of respiratory oxygen consumption, suggesting that short-term control mechanisms were triggered; it also resulted in time-dependent increase in photosynthetic activity and chlorophyll content, suggesting long term control of the photosynthetic apparatus. NH 4 + supply also resulted in a resumption of growth, in light but not in darkness. It is proposed that the use of NH 4 + in darkness by N-limited cells serves to recover from N-limitation, whereas in light it serves to sustain both recovery and growth. This could also explain why cells which are in an N-sufficient status and need nitrogen for growth only, exhibited exclusively a light-dependent NH 4 + uptake.