Abstract
The development of photosynthetic capacity and photorespiration during chloroplast development in 7-day-old etiolated oat (Avena sativa L.) primary leaves was investigated together with changes in the activity of possible NH3-assimilating enzymes. The development of photosynthetic CO2 fixation and photorespiration capacity, and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and glutamine synthetase (GS) activities comparable to green leaves were completed within 48 h of continuous illumination. Chlorophyll synthesis and glutamate synthase (GOGAT) activity continued to increase beyond this time. Within this 48-h period, the activities of Rubisco, GS and GOGAT increased 2.3, 2 and 3 times repectively. Throughout the greening treatment, the GS and GOGAT activities were always high enough to sustain the expected rate of photorespiratory NH3 production. In contrast, glutamate dehydrogenase activity decreased during greening, and its measured rate was not high enough for photorespirtory NH3 assimilation. These results support the idea that the GS/GOGAT pathway is the major, if not the only, route for photorespiratory NH3 assimilation in the light in leaves of higher plants.
Published Version
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