The uptake of carbohydrates and nitrate by Catharanthus roseus cell suspension cultures was studied in relation to biomass production in shake flasks. Biomass production was similar when using either 6, 12, 18, or 24 mM nitrate as the nitrogen source and 20 g L-' sucrose as the carbon source. In all cases, maximum biomass production was reached when carbohydrates were entirely consumed by the cells. Apparent biomass yields, YxIs and YX", were 0.49 g biomass g-' glucose equivalent and 0.23 g biomass mmol-' nitrate, respectively. The determination of the cellular carbon-to-nitrogen ratio (C/N ratio) resulted in the identification of three distinct growth phases: an active growth phase, an accumulation phase, and a biomass decline phase (endogenous metabolism). The onset of the last two phases was correlated with nitrate and sugar exhaustion, respectively. Balanced stoichiometric equations describing the active growth and accumulation phases were proposed based on elemental composition and ash content of the biomass. The stoichiometric equation related to the accumulation phase predicts that the available sugars are stored as starch-and lipid-like materials. Key words: carbohydrate and nitrate uptake Catharanthus roseus cell suspension culture cellular C/N ratio growth phases stoichiometry * To whom all correspondence should be addressed.
' Empirical formula of stearic acid: CH~(CH~)I~COOH.