Photosynthetic characteristics of photoautotrophically grown tobacco callus cells

Haploid callus cells of tobacco (Nicotiana tabacum) were grown photoautotrophically on a solid agar medium in the absence of sucrose in Petri plates in an atmosphere of 1% or 3% CO₂ in air. The averages of dry weight increases for four to five consecutive passages were 2.3- to 3.6-fold per 3-week passage for different subclones. Photosynthetic ¹⁴CO₂ assimilation was maximum at about 1% CO₂ with half-maximal rates obtained at 0.2% CO₂. At saturating CO₂ concentration the average rate of CO₂ fixation was about 5 μmole per gram fresh weight per hour or about 125 μmole per mg of chlorophyll per hour.