Relationship of respiratory pathways in soybean cell suspensions to growth of the cells at various glucose concentrations

Abstract

Green soybean cells (Glycine max L.) were grown in suspension culture on B₅-medium containing various glucose concentrations (2%, 4% or 8% glucose and 2% glucose + 2% or 6% mannitol). Respiratory parameters have been determined in these cells in relation to growth.

The length of the growth phase and the amount of dry weight produced increased with higher glucose concentrations. In cells cultured in the presence of 2% glucose, 4% glucose or 2% glucose + 2% mannitol, the activity of the cytochrome pathway (V _cyt )and the capacity of the alternative pathway (V _alt )were not significantly different. Also the contribution of the alternative pathway to total respiration was essentially the same.

The glucose content of cells grown in 2% or 4% glucose was roughly equal, which might explain the absence of any effect of the increased glucose concentration on the respiratory parameters.

In cells grown in 8% glucose or on 2% glucose + 6% mannitol, both the activity of the cytochrome pathway and the capacity of the alternative pathway were lower. High values of ρ (approaching 1) were found in these cells, meaning that the alternative pathway is nearly fully operative. This is probably caused by the impairment of the cytochrome pathway due to the high osmotic value of the medium.

ATP-production per batch per day has been calculated from oxygen uptake data, integrated and compared with cellular dry weight production to give values of 13-15.3 g dry weight produced mole ATP^-1.

The described experiments produce no direct evidence for a function of the alternative pathway as ‘energy overflow’ in soybean cells. The higher alternative pathway activity in the lag phase might be attributed to the great demand for intermediates during this phase.