Effects of CO(2)-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 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.