Propagation by tissue culture is effective for many woody ornamental plants, but propagules often become desiccated and die during the acclimatization period. This loss is due in part to stomata that fail to close in response to the reduced humidity outside of the culture environment. KCl was used in in vitro treatments to determine if an additional K supply would improve microshoot stomatal function and water status during acclimatization. The effects of the KCl treatments upon subsequent microshoot rooting and percent fresh weight gain were also evaluated.

In preliminary experiments, microshoots of the flame azalea (Rhododendron calendulaceum) were subcultured onto modified Woody Plant Medium amended with a wide range of KCl concentrations for various time periods. It was determined that microshoots did not grow well when cultured at in vitro KCl levels above 50 mM, so treatments were adjusted to 0, 30, and 60 mM KC1, with 9 days of in vitro exposure. After treatment, percent tissue K was determined by atomic absorption spectrophotometry and microshoot water potentials were measured by thermocouple psychrometry.

The capacity for the microshoots to resist desiccation after in vitro KCl treatment was determined by percent rooting and fresh weight gain after exposure to dehydration stress, and by gravimetric weight loss of microshoots placed in isopiestic tubes. In addition, microshoots from in vitro KCl treatments were evaluated for percent stomatal closure and water potential during a 38-day acclimatization period.

In vitro KCl treatments induced elevated tissue K levels in microshoots and reduced microshoot water potentials, but it could not be shown that these effects specifically enabled the microshoots to resist desiccation. Rooting and percent fresh weight gain were not affected by in vitro treatments, nor was gravimetric weight loss. Microshoot maturation, as a function of days out of culture, had the greatest effect upon increased stomatal function, which, coupled with the onset of rooting, improved microshoot water status.