Regulation of cell division and cell enlargement by turgor pressure.

Isolated radish (Raphanus sativus L., var. Red Prince) cotyledons were incubated in growth medium plus graded concentrations of mannitol (-1 to -16 bars) for 28 hours. At the end of the incubation period, turgor pressures were measured using thermocouple psychrometers. Cell division, as measured by DNA increase, was greatly stimulated by increasing turgor from 5 to 6 bars. Cell enlargement was stimulated as turgor increased above 3 bars. The critical turgor pressure for increased cell division thus appeared significantly greater than that for increased cell enlargement.