STUDIES ON GROWTH IN CULTURE OF PLANT CELLS .4. INITIATION OF DIVISION IN SUSPENSIONS OF STATIONARY-PHASE CELLS OF ACER PSEUDOPLATANUS L

Techniques are described whereby a culture medium can be 'conditioned' by separation from a dense cell suspension either by a sinter or by a dialysis membrane. The enhanced growth-promoting activity of the conditioned, as compared with a new medium, is revealed by using a low density of cells (15 × 103 or less cells per ml) to initiate the test cultures from a stationary-phase suspension. The optimum pH of the conditioned medium is c6.4. To obtain a conditioned medium of high activity it is necessary to use an appropriate volume ratio of culture medium to conditioning cell suspension and to limit the conditioning period. Conditioning of the culture medium reduces by a factor of 10 (i.e. down to c. 1000 cells per ml) the minimum effective cell density needed for self-sustaining growth. There therefore exists a population-dependent requirement which is not met by the conditioned medium as now prepared. The retention of the activity of the conditioned medium in various situations has been studied as a preliminary to work on the chemical basis of conditioning. © 1969 Oxford University Press.