Photosynthesis by carrot tissue cultures

Abstract

¹⁴CO₂-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 ¹⁴CO₂-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.