The effect of inoculum size on the growth of cell and root cultures of Hyoscyamus muticus: Implications for reactor inoculation

Cell suspensions inoculated at low cell concentrations displayed a typical growth reduction, whereas root cultures displayed an improvement in growth. Specific growth rate of Hyoscyamus muticus cell suspensions decreased from 0.25 to 0.12 d^-1 as inoculum concentration was reduced from 4.0 to 0.02 g fresh weight per liter. In contrast, roots show an increase in growth rate from 0.24 to 0.43 d^-1. These contrasting growth patterns can be explained as the result of: a) the high specific surface area of cells as compared to roots and, b) the differentiated structure of roots. The dispersed nature of cell suspensions makes them more prone to leakage of key growth factors/cellular contents to medium. The results of this work indicate that cell cultures require substantially higher inoculum concentrations. In contrast, roots can be inoculated at very low concentrations. These facts imply that whereas seed vessels must be employed by cell suspensions, their use for root cultures is a compromise between an easier handling of an entwined root mass and the reduction of the contamination risk of large medium volumes.