[Hormonal regulation of petiolar abscission in Coleus rehneltianus explants : II. The possible role of abscisic acid in the abscission process].

In extracts of Coleus rehneltianus shoots abscisic acid was identified by thin layer chromatography and by spectropolarimetry.Diffusates from the petiole of isolated leaves were tested in an abscission test. According to previous results (Part I) these experiments allow conclusions concerning the hormonal flux from the lamina.The next step was to separate the diffusates by paper chromatography. The relative amounts of IAA and ABA were estimated on the basis of a biological assay. Young leaves yield ten times as much IAA to an agar receptor as green adult leaves and twenty times as much as yellow senescent leaves. On the other hand young leaves do not transmit detectable amounts of ABA to the receptor. Diffusates from adult leaves contain only a small amount of ABA, whereas those of senescent leaves contain a considerable amount.Evidently the induction of leaf abscission is not effected by a strong decrease of the IAA content during the development of a young leaf into an adult leaf. One is lead to assume that the rapid increase of the ABA flux during senescence is responsible for the induction of the abscission process.