Mobilization of Seed Indole-3-Acetic Acid Reserves During Germination

Abstract

Seeds contain conjugates of indole-3-acetic acid (IAA), the gibberellins, the cytokinins, and abscisic acid. Hormones other than IAA will not be reviewed in this work and have, been reviewed elsewhere (e.g. Ref. 2). In addition, seeds contain auxins other than IAA as, for example, phenylacetic acid² and the 4-chloroindole-3-acetic acid of Gander and Nitsch et al, Marumo et al, and Engvild et al, and have been previously reviewed^2–4 and will not be considered here. Further, the bulk of this work will be addressed to the seedling of Zea mays since this has been the major subject of our research. It is hoped that by means of these omissions that greater attention and concentration may be centered on the many mysteries and uncertainties concerning the seed as a source of IAA for the growing vegetative tissue of the shoot. The greatest mysteries, of course, are those that have frequently been mentioned throughout this volume including how the shoot “tells” the seed at what rate the reserves should be mobilized and transported, and in the case of the monocotyledonous seedling how materials are moved from the endosperm into the scutellum, from the scutellum into the vascular stele, and from the stele into the vegetative tissue. We can only allude to these important determinants of the early stages of shoot growth in the hope they receive further attention. In the spirit of this belief I hope you will tolerate an introduction that is almost as long as the body of the text.