Effects of CO2-Enrichment and of Aminoacetonitrile on Growth and Photosynthesis of Photoautotrophic Calli of Nicotiana plumbaginifolia

Photoautotrophic calli of Nicotiana plumbaginifolia were grown for 3 weeks under two CO(2) concentrations (500 and 20,000 microliters of CO(2) per liter). Calli cultured at high CO(2) exhibited a two-fold higher rate of growth. At CO(2) test levels, these calli were characterized by a lower net photosynthetic capacity than calli cultured at low CO(2). This diminution due to CO(2) 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 CO(2) grown calli contained about 5.5-fold more sucrose and three-fold less orthophosphate (Pi) than low CO(2) 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 CO(2). In calli grown at low CO(2) 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 CO(2) uptake decreased by about 60% at 340 microliters of CO(2) per liter and 35% at 10,000 microliters of CO(2) 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 CO(2). In photoautotrophic calli, the inhibition of the glycolate pathway by AAN results in severe perturbations in glutamate metabolism and in chlorophyll biosynthesis.