Photosynthesis by carrot tissue cultures

Abstract

(14)CO2-fixation rates in green carrot callus cultres (about 35 μg chlorophyll/g fresh wt) were determined in gaseous and liquid media using a range of light intensities and CO2 concentrations. Main products of light-dependent CO2-fixation were sucrose, alanine, glutamine, serine/glycine and malic acid. In darkness, glutamine and malic acid were formed.Light CO2-fixation rates were about ten times higher than dark fixation rates and reached 50-90 μmol/mg chlorophyll/h in 10000 lux, 1% CO2 in air. Net O2-evolution by the tissue was demonstrated polarographically under these conditions. Light CO2-fixation rates were linearly related to chlorophyll levels while dark fixation was independent of chlorophyll content. Lowered O2 partial pressures in gaseous conditions increased (14)CO2-fixation rates. Ribulose diphosphate carboxylase and phosphoenol pyruvate carboxylase activities and their distribution in subcellular fractions were examined.When carrot tissue cultures were grown for two or four weeks on agar media lacking a carbohydrate source, in 10000 lux and 1% CO2 in either air or N2, dry weight increases were obtained although chlorophyll levels eventually declined.