p-Hydroxybenzoic Acid, a Growth Regulator, Isolated from Woody Cuttings of Ribes rubrum

Woody cuttings of Ribes rubrum, an easy plant to root, were extracted with methanol. One fraction of this extract was both water and ether soluble; a part of it was only water soluble. From the water and ether soluble fraction a crystalline compound was isolated which was fully identified with p-hydroxybenzoic acid (PHB) by m.p., mixed m.p., infrared spectrum, ultraviolet absorption in neutral and alkaline methanol and chemical analyses. For Avena coleoptiles straight growth test, p-hydroxyhenzoic acid was found to have a significant growth promoting activity in the range 20–100 μg/ml. and it showed strong growth inhibition at concentrations higher than 200 μg/ml. From the same extract fraction a phenolic ester was isolated by paper chromatography which showed a weak growth inhibiting activity. This compound was identified as an ester of p-hydroxybenzoic acid by micro-scale reactions. From the extract soluble only in water further amounts of crystalline p-hydroxybenzoic acid were obtained by alkaline hydrolysis. This PHB may have arisen from the breakdown of pelargonidin glucosides.