Studies on the Growth in Culture of Plant Cells I. GROWTH PATTERNS IN BATCH PROPAGATED

Techniques are described for following increases in total cell number, fresh weight and dry weight, and changes in mean cell size, and in the relative number of free cells to cell aggregates during the growth of batch-propagated suspension cultures of tissues derived from several species of angiosperms. When total cell number is plotted against time it is seen that there can be distinguished in sequence a lag phase, phases of acceleration, maximum rate, and negative acceleration of cell division and, finally, a stationary phase. Studies with Partheno cissus tricuspidata crown-gall tissue, growing in a synthetic liquid medium, have shown that the total cell production per culture in the first instance is limited by nitrate supply rather than by the supply of other inorganic ions, sucrose supply, aeration, or the release of endogenous inhibitors. Studies, particularly with Acer pseudoplatanus tissue, have shown that during the period of high cell division rate, mean cell size reaches its minimum value and average number of cells per cell aggregate its maximum value. Cell separation does not occur to a signi ficant extent until cell-division activity has almost ceased and it is dependent upon cell expansion. The balance between cell division and cell expansion determines the 'cellular unit' composition of the cultures. Refinement of the control of growth patterns in plant suspension cultures calls for further study of the 'condi tioning' of media, of factors which limit the duration of the period of high mitotic activity, and of the conditions necessary for full and rapid cell expansion.