Premium
LIGHT‐DEPENDENT DECLINE OF NH 4 + ASSIMILATION UNDER CO 2 DEPRIVATION IN N‐LIMITED CHLORELLA SOROKINIANA (CHLOROPHYCEAE) 1
Author(s) -
Rigano Vittoria Di Martino,
Vona Vincenza,
Esposito Sergio,
Martino Catello,
Rigano Carmelo
Publication year - 1990
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.0022-3646.1990.00069.x
Subject(s) - chlorella sorokiniana , carboxylation , chemostat , ammonium , photosynthesis , biology , chlorella , darkness , ammonia , scenedesmus , nitrogen assimilation , botany , biochemistry , nitrate , biophysics , nuclear chemistry , algae , chemistry , ecology , organic chemistry , bacteria , genetics , catalysis
Cells of Chlorella sorokiniana Shihira & Krauss 211/8k, grown in a chemostat under conditions of nitrate limitation, assimilated ammonium in light (307 ± 12 μmol · mL packed cell volume (pcv) −1 · h −1 ) and darkness (305 ± 30 μmol · mL pcv −1 · h −1 ) at similar rates when supplied with air containing 5% CO 2 . Ammonium assimilation in cell suspensions flushed with pure nitrogen to establish anaerobic conditions was almost totally prevented both in darkness and in light. Cell suspensions flushed with CO 2 − ‐free air and grown in the dark assimilated ammonium at a rate of 314 ± 23 μmol · mL pcv −1 · h −1 . Light assimilation was 128 ± 10 μmol · mL pcv −1 · h −1 , a rate which was only 41% of that in darkness. Resupply of ammonium to N‐limited chemostat cells resulted in a 3.5‐fold stimulation of dark respiration and a suppression of photosynthetic O 2 evolution. We hypothesize that the partial decline of ammonium assimilation in Chlorella 211/8k in the light under conditions of limited CO 2 supply is due to the fact that the photosynthetic carboxylation reaction competes with the dark carboxylation reaction for the available CO 2 , and that the production of C 4 and C 5 precursors foramina acid biosynthesis will be slower than in the dark. Alternatively we suggest that an increase in the concentration of photogenerated compound(s) not used for CO 2 assimilation attains an intracellular level suitable to trigger a control mechanism operating at the level of starch break‐down or glycolysis.