Studies in Dormancy of Sycamore I. Seasonal Changes in the Growth-substance Content of the Shoot

Abstract

The growth substances present in buds and leaves of sycamore (Acer pseudoplatanus) have been studied throughout the annual cycle, in relation to the growth and dormancy of the shoot. Extracts made with 8o per cent. methyl alcohol of the apical region and mature leaves were chromatographed and assayed with wheat coleoptile sections, lettuce seeds, cress-roots, and leaf-disks of 8ycamore. An inhibitor was present in all extracts, running at approximately Rf 0.7 on chrornatograms developed in isopropanol/ammonia. This was found to show various quantitative changes during the course of the year. Extracts of the apical region showed greatest inhibiting activity in the early winter, and least when active growth was taking place in May—June. There appeared to be a gradual decrease in inhibitor content of the terminal-bud during the course of the winter. During late summer and early autumn the inhibitor content of the apex increased. Extracts of the mature leaves made during summer and autumn showed that the inhibitor content of the leaves increased until late August, and then decreased to zero. This latter change is thought to be associated with the senescence of the leaves prior to ab8cission. Indirect evidence suggests that the inhibitor is formed in the leaves and transported to the apex, where it accumulates. The inhibitor was found to inhibit the growth of sycamore tissue itself. Growth-promoting activity was found on most of the chromatograms, and it was shown that this was attributable to sugar rather than auxin.