A novel root inducer, 4-(3-indolyl)-4-butanolide (IBL), is formed at an early stage in Bupleurum falcatum L. root cultures containing indole-3-butyric acid (IBA)

We found a novel indolebutyric acid (IBA) derivative, 4-(3-indolyl) butanolide (IBL), produced at an early stage during Bupleurum falcatum L. (known as Saiko in Japan) root culturing. Another IBA derivative, 4-[3-(2-oxo-indolyl)]butyric acid, was also detected, but this compound appeared to have an abiotic origin. Synthetic IBL induced rooting in cultured roots of B. falcatum and induced rooting in cuttings of Vigna radiata. The root-inducing characteristics of IBA and IBL were different. IBA induced considerable thickening of the original roots of B. falcatum, because of marked cell expansion and division in the cortical tissue, before new roots emerged, a typical response to auxin. IBL, on the other hand, did not cause cell expansion, but it induced cell division in the cortical tissue as strongly as IBA did. IBL has the potential to become an excellent, industrially used root inducer, and it serves as valuable tool for research on root induction, because of its unique root-inducing activity.