AUXIN DESTRUCTION AND GROWTH IN JAPANESE MORNING GLORY STEMS *

The Japanese morning glory, Pliarbitis nil Choisy, has been a source of beauty and inspiration to Japanese gardeners for centuries. It is not surprising, therefore, that, following the rediscovery of Mendel’s work, Japanese scientists turned to the many horticultural varieties of this plant as a natural object for the study of inherited traits. During subsequent decades a great body of genetic knowledge accumulated which included the characterization of numerous mutants affecting growth (see for example Takenaka, 1958). In 1960 workers at the National Institute of Genetics in Mishima received seeds of some new horticultural varieties among which were discovered two tumor-forming strains. A genetic analysis by Takenaka and Yoneda (1963, 1965) indicated that tumors were formed as a result of the presence of several mutant genes, each of which alone induced growth abnormalities. The mutations that appeared to contribute most significantly to tumor formation were a dominant gene, “Blown” (B), and two recessive genes, “feathered” (fe) and “delicate” (dl) . The fact that it is possible to study the effects of each of the mutations affecting growth separately as well as in combination has led us to undertake an investigation on the nature of the physiological changes brought about by these, and other, mutants, in the hope that such an investigation will elucidate the mechanisms concerned with both normal and pathological growth. Stems of plants possessing either the feathered, or the delicate, gene exhibit an irregularly diminished ability to elongate. Our preliminary experiments ascertained that it was sometimes possible to reverse this diminished ability to elongate by applying indoleacetic acid (IAA), or gibberellin. This suggested that, associated with these two mutations, is an abnormal growth hormone metabolism. In order to understand the mutant pattern, we felt it necessary to first study the pattern observed in a wild-type strain. It is this study which led to the discovery of a group of substances which appear to be paramount in regulating auxin metabolism in Japanese morning glory stems and which probably occur widely in nature, Much of this work has been published elsewhere (Yoneda & Stonier, 1966; Stonier & Yoneda, 1966) and will thus be reviewed here only briefly.