Photoautotrophy of Spinach Cells in Continuous Culture: Photosynthetic Development and Sustained hotoautotrophic Growth

Abstract

Photosynthetic development of Spinacia oleracea L. (spinach) cells was ‘triggered’ by halving the supply of sugar to a continuous culture. This was demonstrated between two steady states at constant specific growth rate (4.2 ± 0.17 × 10⁻³ h⁻¹). As a direct consequence of this ‘trigger’ the cells were in conditions of sugar famine, demonstrated by organic carbon balance. Comparison of the biomass was made between the two steady states. It was found that in sugar famine the biomass contained 8 times as much chlorophyll and the ratio of photosynthesis to respiration in saturating conditions had increased 22 times, when compared to the biomass in condition of sugar excess. All substrate carbon and organic factors were then removed from the fresh medium, carbon dioxide and photosynthetically active radiation (PAR) were increased. In these photoautotrophic conditions three further steady states were established. The effects of increasing the dilution rate and then increasing PAR were examined. Growth was found to be limited by PAR. The photosynthetic yield Y of photoheterotrophic spinach cells in fructose famine was estimated as 0.004 g kJ⁻¹ PAR. In photoautotrophic conditions the maximum Y was 0.0018 g kJ⁻¹. It was suggested that this lower yield was due to chloroplast development being arrested by an unknown factor.