The Influence of Water Stress and Abscisic Acid on the Root Development ofChrysanthemum MorifoliumCuttings During Propagation

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Abstract
Abscisic acid (± ABA), at 10-4 M, induced almost complete stomatal closure in isolated epidermal strips of Chrysanthemum morifolium, and in cut shoots when taken up in the transpiration stream. ABA sprayed onto intact leaves was less effective. In the greenhouse ABA reduced the water loss of cuttings under conditions of low humidity, and stimulated root growth, although the hormone did not improve either the water content or rooting performance of cuttings under mist. It was not clear whether the stimulation of root growth by ABA, in the absence of mist, was due to a direct influence of the hormone on root development or to its action as an antitranspirant, since highly stressed cuttings demonstrated a rooting performance equivalent to the most effective ABA treatment, despite differences in relative water content. Since ABA and other endogenous growth regulators can be produced in water-stressed tissue, their influence on root development during the propagation of leafy cuttings is briefly discussed.