Root‐promoting Substances in Salix alba

Abstract

AbstractRoot‐promoting substances were extracted from softwood cuttings of Salix alba L. by centrifuging them with water or by shaking the ground freeze‐dried stems with water. Rooting substances were partitioned by paper chromatography or chemical fractionation and their rooting activity was tested by mung bean cuttings. Both extracts indicated three major root ‐promoting fractions at Rf 0‐0.1, 0.7‐0.8, and 0.3‐0.4 in a decreasing order of their activities when paper chromatographed with isopropanol:ammonia:water 8:1:1 v/v. The strongest one indicated an apparent synergistic rooting effect with indol‐3yl‐acetic acid (IAA) regardless of the extraction method. These results indicate that water can extract from freeze ‐dried sample the similar rooting substances found in the centrifugal diffusates. The Rf 0–0.1 fraction consisted of at least four fractions and the strongest one did not move from the starting line on the chromatogram when isopropanol:ammonia:water 8:1:1 was used. This starting line fraction was extremely strong in rooting activity and its highest concentration resulted in 8.7 times as many roots as controls. More thain additive rooting effect between IAA and the fraction was found only at the highest concentration. The fraction was very soluble in water but insoluble in chloroform or ethyl ether and only stimulated rooting of mung bean cuttings when it was applied within 3 days after cuttings were made. It had no effect in lengthening roots. The starting line fraction was further found to have four root‐promoting subfractions at Rf 0.05, 0.35, 0.65, and 0.85 when it was chromatographed in 60 % isopropanol. Among these four, the subfractions at Rf 0.65 and 0.35 were strongly root promotive and displayed more than additive root promotion with IAA at the highest concentrations studied.