Relationships between nucleic acid, nitrogen, and growth rate of tobacco cells in suspension culture

Abstract

Changes in the amount of nucleic acid and nitrogen, and the relationships between these amounts and the growth rate of tobacco cells (Nicotiana tabacum L. cv. Bright Yellow-2) at different initial nitrogen concentrations in the medium, were examined in batch cultures. During culture in basal medium, the amount of intracellular nucleic acid expressed per unit of dry biomass was 36.3 mg RNA g−1 cell and 8.1 mg DNA g−1 cell at the beginning of batch culture. These values increased 2.5 fold for RNA and 1.5 fold for DNA during the exponential growth phase and then gradually decreased with the decline in the growth rate. Similar changes were also observed in the medium containing less nitrogen. The specific growth rate, μ (day−1), of the culture corresponded to the magnitude of the intracellular RNA content (mg RNA g−1 cell), and the linear relationship, RNA=38μ+23 was obtained. In addition, there were remarkable positive correlations between the total and protein nitrogen, and μ during the cultures. The mononucleotide composition of total RNA (AMP+UMP)/(GMP+CMP) which was suggested to be a convenient index of metabolic activity was nearly constant (0.78 to 0.80) during tobacco cell culture in the basal medium.