Effects of CO2-enrichment and of aminoacetonitrile on growth and photosynthesis of photoautotrophic calli of Nicotiana plumbaginifolia.
Rey P. | Eymery F. | Peltier G.
Photoautotrophic calli of Nicotiana plumbaginifolia were grown for 3 weeks under two CO2 concentrations (500 and 20,000 microliters of CO2 per liter). Calli cultured at high CO2 exhibited a two-fold higher rate of growth. At CO2 test levels, these calli were characterized by a lower net photosynthetic capacity than calli cultured at low CO2. This diminution due to CO2 adaptation could be ascribed to a 170% stimulation of dark respiration, a 40% decrease in total ribulose-1,5-bisphosphate carboxylase (Rubisco) activity, and also to a feedback inhibition of photosynthesis: high CO2 grown calli contained about 5.5-fold more sucrose and three-fold less orthophosphate (Pi) than low CO2 grown calli. Whether the decrease in Rubisco activity is related to the accumulation of sucrose and to the Pi limitation is discussed. Both calli exhibited a Warburg-effect showing the existence of active photorespiration at low CO2. In calli grown at low CO2 with 5 millimolar aminoacetonitrile (AAN), an inhibitor of the glycolate pathway, fresh weight decreased by 25% and chlorophyll content by 40%, dark respiration increased by 50% and net CO2 uptake decreased by about 60% at 340 microliters of CO2 per liter and 35% at 10,000 microliters of CO2 per liter. In these calli, glutamine and glutamate contents were half of control calli. In contrast, AAN did not provoke any noticeable effect in calli grown at high CO2. In photoautotrophic calli, the inhibition of the glycolate pathway by AAN results in severe perturbations in glutamate metabolism and in chlorophyll biosynthesis.
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