ON HORMONES AND WEEPING: ASYMMETRIC HORMONE DISTRIBUTION AND THE PENDULOUS GROWTH HABIT OF THE WEEPING MULBERRY, MORUS ALBA VAR. PENDULA

Abstract

The possibility that asymmetric hormone distribution causes downward bending of weeping mulberry (Morus alba var. pendula) twigs was investigated. By extraction, bioassay and gas chromatography it was shown that while upper and lower twig sections had no differences in auxin activity, the two sides differed considerably in content of GA and ABA. The lower side contained high levels of endogenous GA while the upper side had higher concentrations of ABA. The significance of these results and their possible role in the weeping habit of tree growth are discussed. It is suggested that the high GA levels coupled to low ABA content induce greater lignification on the lower side of the twig and that this tissue is less sensitive to auxin and has a lower growth response than the upper side of the twig thus causing a downward inclination of growth. Copyright © 1974, Wiley Blackwell. All rights reserved