Root-stimulating activity from various gelling agents used in tissue culture.
Extracts of gelling agents have been shown to stimulate rooting and this study was initiated to investigate the presence of root stimulating substances in gelling agents. After screening a number of gelling agents, four were selected, namely; Agar Bacteriological, Agar Commercial Gel, Difco Bacto Agar and Gelrite were selected and examined for the presence of root-stimulating substances using mungbean bioassay. Water extracts of Agar Bacteriological, Agar Commercial Gel and Difco Bactol Agar stimulated rooting of mungbean cuttings. Addition of Charcoal neither reduced nor increased rooting produced by the water extract of the first two agars but when added in conjunction with Difco Bacto Agar rooting was reduced. Autoclaving, however reduced rooting in extracts of the gelling agents. The possibility that root-stimulating substances may not be the same in all the gelling agents can not be excluded. Extraction of Gelrite with water was problematical and was therefore excluded. IBA solution and water extracts of the gelling agents separately promoted good rooting in mungbeans cuttings. Rooting in extracts of autoclaved frozen-thawed gelling agents was poor, however, IBA + gelling agents gave high rooting at the 100% concentration and this could possibly be due to an additive effect of the IBA. Addition of charcoal reduced rooting significantly in extracts of IBA + gelling agents. Using 80% acidic methanol, reasonable levels of rooting substances were obtained from the residue extract of this complex (IBA + gelling agent+charcoal) of all the gelling agents except Gelrite indicating that root-promoting substances were adsorbed by charcoal. The low rooting in the presence of the Gelrite extract was attributed to the matrix of the polymer of the Gelrite. Ethyl acetate fractionated extracts (EA-pH 8.0; EA-pH 3.0; and Aqueous) obtained from the four gelling agents stimulated rooting indicating the presence of numerous root promoting substances. Gelrite gave good rooting with both the 50 and 100% concentrations of all the fractions. Purified water and ethanol extracts of the gelling agents exhibited auxin-like activity when separated by paper chromatography and compared with IBA and IAA standards. Using HPLC, IAA was quantified in all the gelling agents with Difco Bacto Agar and Agar Commercial Gel having the highest IAA concentration and Gelrite the lowest IAA concentration. IAA concentration in Agar Bacteriological was a third of the level detected in Difco Bacto Agar. The information from this work may enable researchers to consider gelling agents as sources of auxin-like compounds and other plant hormones as well as support media for use in tissue culture procedures and also increase the enthuse for further research into the nutrient types and levels in gelling agents.