Effect of sucrose, exogenous product concentration, and other culture conditions on growth and steroidal alkaloid production by Solanum aviculare hairy roots

Abstract

Growth and steroidal alkaloid production by Solanum aviculare hairy roots were investigated as a function of temperature, initial sucrose and exogenous solasodine concentrations, and medium osmolality. Root growth measured as dry weight was significantly affected by initial sucrose concentrations between 2 and 12%; however, sucrose levels below 6–9% did not significantly alter the specific alkaloid content. Biomass production was maximum and about 60% higher than in 3% sucrose medium when the initial sucrose concentration was 4–6%. The effect of sucrose concentration on growth could not be attributed to osmotic effects, starch accumulation in the roots, or sugar depletion at the lower sugar levels. No significant difference at the 0.01 level in growth rate or alkaloid yield was found between seven root clones cultured in either 3 or 6% sucrose medium. The minimum root doubling time occurred at 25°C; doubling times at 20°C, 30°C, and 37°C were between 1.1 and 3.4 times higher. Experiments with exogenous solasodine added to the medium revealed that growth is strongly inhibited by extracellular product concentrations as low as 2 mg l −1. Nett steroidal alkaloid production declined to negative values when more than 10 mg l −1 solasodine was added, indicating that degradation or conversion of solasodine occurred. As extracellular concentrations can reach at least this level in batch culture, in situ removal of product is recommended for solasodine production systems.