Regulation of Cytoplasmic and Vacuolar Volumes by Plant Cells in Suspension Culture

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Abstract
Quantitative microscopical measurements were made of the proportion of cell volume occupied by cytoplasm in a cell suspension culture derived from cotyledons of bush bean (Phaseolus vulgaris cv. Contender). On a 7 day culture cycle, the content of cytoplasm varies from 25% at the time of transfer to 45% at the start of the phase of rapid cell division. If the culture is continued beyond 7 days, the vacuole volume reaches 90% of cell volume by day 12. Attempts to measure relative cytoplasmic volumes by compartmental analysis of nonelectrolyte efflux were unsuccessful. The proportion of cell volume occupied by cytoplasm is roughly correlated with protein content, but shows no correlation with cell size or with intracellular concentrations of K or Na. The most striking observations is that the growth of cytoplasmic volume for the culture as a whole appears to be constant throughout the culture cycle, despite changes in the rate of cell division, cell size, rate of increase in fresh or dry weight, amount of cytoplasm per cell, the cellular concentration or fluxes of Na or K, and the rate of vacuolation. Cytoplasmic volume is apparently under the control of its own regulatory mechanism, which operates to give a constant exponential increase in cytoplasmic volume independently of most other observed cellular properties.