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Effect of Eucalyptus Growth Regulators on the Water Loss from Plant Leaves

Department of Botany, Australian National University, Canberra, A.C.T., 2600, Australia

Three closely related growth regulators (G) that are present in some myrtaceous plants were examined for possible anti-transpirant effects. The bioassay material involved cuttings of mung bean and Eucalyptus rupicola. Stomatal resistance was determined by a diffusion porometer. Water loss was equated with water uptake by the cutting over a 24-hour period.

In both bioassays, G reduced water loss. The reduced water loss was associated with stomatal closure. This anti-transpirant effect of G was five to ten times less than that of abscisic acid. The stomatal resistance to the diffusion of water vapor from mung bean leaves increased within 1 hour of application of G. Marked stomatal closure occurred after 6 hours when 5 to 7 micrograms of G had accumulated in the leaves.

These results and earlier evidence, suggest that G growth regulators are involved in the water economy of Eucalyptus and perhaps other related genera.