Reduction of Water Loss during ex vitro Acclimatization of Micropropagated Digitalis lanata Clone Plants

In-vitro-grown shoots and clone plants of Digitalis lanata showed high rates of transpiration if placed in dry air. The easy loss of water was due to morphological and physiological abnormalities. Leaves of in-vitro-grown shoots and plants had a much thinner cuticle than greenhouse-grown plants and had less epicuticular lipids. Guard cell walls were not flexible enough to allow closure of the stomata. Stimuli like the withdrawal of K⁺ and BA, or the application of A1³⁺ and ABA caused a reduction of the stomaaal aperture, but not complete closure. No change in aperture was obtained after the application of CO² or the withdrawal of light. Stomata of vitrified leaves showed no response to any of the stimuli examined. The leaves formed in vitro were unable to develop further ex vitro. After a few weeks in the greenhouse they were replaced by newly formed physiologically normal leaves.