Hormonal control of radial and longitudinal growth in the tree stem

TLDR: A review of the evidence implicating the currently recognized hormone classes in the regulation of radial and longitudinal growth in the stem and shoots of woody species can be found in this paper.

Abstract: Publisher Summary This chapter reviews the evidence implicating the currently recognized hormone classes in the regulation of radial and longitudinal growth in the stem and shoots of woody species. Emphasis is placed on investigations that used temperate-zone tree species as the experimental material, and modern physicochemical or immunoassay techniques to identify and measure endogenous hormone levels. Understanding the roles of hormones, and the mechanisms regulating their absolute and relative levels, not only would significantly increase our basic knowledge about how trees grow and develop, but could also have practical applications, for example, in the development of methods for early screening of inherently fast growth in breeding programs, and for using genetic engineering to alter traits such as wood quantity, and quality and tree form. Auxins, gibberellins, cytokinins, and abscisic acid have been conclusively identified, typically, by combined gas chromatography–mass spectrometry either in whole shoots or more specifically in buds, leaves, stem, cambial region, or xylem sap. The significance of hormones in the regulation of cambial and longitudinal growth in woody shoots is still unknown, although at least some of them most likely play key roles. The use of genotypes with different growth capacity and crown form is increasing and should help in defining the role of each hormone. It seems likey that IAA and GAs are essential for the division of cambial cells and the differentiation of their derivatives; that CKs are necessary for bud expansion; with GAs and optimal levels of IAA being required for rapid shoot elongation.