Further studies on the relationship between the rates of nitrate uptake, growth and conductivity changes in the medium of plant cell suspension cultures

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Abstract
The changes in packed cell volume and in nitrate content and conductivity of the medium during the growth cycle of cell suspension cultures from Petroselinum hortense Hoffm., Glycine max Merr., and Haplopappus gracilis A. Grey in a chemically defined medium were compared. In all three cases sigmoidal curves obtained for large decreases in the conductivity were paralleled by similar curves for the rates of nitrate depletion from the medium until this nutrient was completely exhausted. Further decreases in the conductivity subsequent to nitrogen starvation proceeded at relatively slow rates and ceased when the cultures entered into the stationary phase of the growth cycle. Thus the previously reported method of deriving growth curves indirectly from conductivity measurements (Hahlbrock and Kuhlen, Planta 108: 271–278, 1972; Hahlbrock et al., Planta 118: 75–84, 1974) might be generally applicable for this particular medium. The method seems to be based on a continuous uptake by the cells of ionic constituents throughout all stages of actual growth, even beyond the stage of nitrate exhaustion. Cell suspension cultures from Cicer arietinum L. and Acer pseudoplatanus L. in two different, more complex media were used for similar experiments, in which the changes in packed cell volume and in the conductivity of the medium were recorded. As with the results obtained with the fully synthetic medium, the mirror-images of the curves obtained for the decline in conductivity initially paralleled the growth curves. However, the two curves became incongruous after a certain growth stage was reached. These results are discussed with respect to the composition of the media used and to the apparent limitations of the method of determining specific growth stages by monitoring conductivity changes in the medium.