ABSOLUTE MEASUREMENT OF CELL EXPANSION IN PLANT-CELL SUSPENSION-CULTURES

A method is described for the measurement of intracellular volume (V(i)) in cell cultures. In principle, any stable compound that neither penetrates the plasma membrane nor binds to the cells can be used to trace the total extracellular (apoplastic) volume and hence to estimate the intracellular volume. No suitable coloured or UV-absorbing compound could be found among those tested; the main problems were binding to the cell surface and/or instability in the medium. However, [C-14]mannitol was an acceptable apoplastic marker, by use of which we showed that 21-47% of total packed cell volume (PCV) was intracellular, and 14-33% of total settled cell volume (SCV) was intracellular. Therefore, measurements of PCV and SCV misrepresent cell expansion to a variable extent. Cultures of Acer, Rosa, Spinacia and Zea achieved final symplastic volumes of only approximately 9, approximately 14, approximately 6 and approximately 6%, respectively, of the total suspension culture volume.