The Effect of Indole-3-Butyric Acid and Riboflavin on the Morphogenesis of Adventitious Roots ofEucalyptus ficifoliaF. Muell. GrownIn Vitro

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Abstract
Shoot explants from seedling-derived culture of Eucalyptus ficifolia F. Muell. cultured on a rooting medium free from indole-3-butyric acid (IBA) develop a root system (Type I) consisting of a few comparatively long roots and only small amounts of callus. IBA at 5.0 μM in a rooting medium free from riboflavin induces the development, on the shoot explants, of a compact root system (Type II) consisting of callus and many short roots. Riboflavin when exposed to light, is able to photo-oxidize IBA; the degree of photo-oxidation depends on the photon fluence of the light received. The rooting response of the cultures reflects the degree of photo-oxidation of IBA: concentrations of IBA from about 10−4M to 10−6M in the rooting medium induce formation of the Type II root system whilst photo-oxidation of the auxin to concentrations of about 10−8M or lower induces the formation of the Type I root system. Thus, exogenous riboflavin and exogenous IBA are linked in a distinct light-induced, riboflavin-mediated change in root morphogenesis. The anatomy of root development in the Type I and Type II root systems was studied and factors affecting the development were defined. Characteristics of riboflavin and IBA breakdown in various light regimes were determined and related to root morphogenesis. The results and their implications are discussed.