Viability of plant cell suspensions exposed to homogeneous ultrasonic fields of different energy density and wave type

Exposure of Pettunia hybrida cell suspensions to ultrasound at a frequency of 2.43 MHz in a standing wave held at an energy density of 70 J m(-3) (pressure amplitude of 0.78 MPa) decreased their mean viability to 35% after 20 min of sonication. A comparison of propagating wave and standing wave treatments at equal frequency (2.15 MHz) and energy density (8.5 J m(-3)) showed, in the first case, a rapid decline in mean viability of cells (to 30% after 10 min of sonication) and, in the second case, a retaining of the initial viability (95%), respectively. Cells sonicated 4 days after subculture were more sensitive than cells sonicated 2 or 6 days after transfer to new culture medium. It was concluded that cellular viability depends primarily on the acoustic energy density, the exposure time, and the mechanical properties of the cells determined by age. As a consequence of the trapping of cells in the anti-node planes of the standing wave, propagating wave fields reduced cellular viability compared with standing wave fields at equal energy density. (C) 2000 Elsevier Science B.V. All rights reserved.