Gibberellins and the Regulation of Shoot Elongation in Woody Plants

Abstract

Perennial, temperate-zone woody plants display a great variety of patterns of shoot elongation. Anatomically, height growth in trees is due to an activity of apical meristem (eumeristem) and subapical meristem (rib meristem, primary elongating meristem). The apical meristem is responsible for most of the organogenic phenomena normally associated with shoot morphogenesis, while the subapical meristem is the major site of cell division and elongation contributing to stem extension.1 Morphologically, shoot growth consists of formation of leaf and node initials and elongation of internodes. In the free growth pattern, characteristic of juvenile stages of many temperate-zone dicotyledonous as well as some coniferous species, these two processes can occur simultaneously. On the other hand, mature stages of most conifers and some deciduous trees have a fixed or determined growth pattern in which stem unit initiation and elongation are separated in time and shoot extension is a result of elongation of these preformed stem units.2,3 The growth pattern is an inherent characteristic of the plant, and species showing various combinations of free and fixed growth can also be found. In addition, the growth pattern of a species normally changes with ontogeny, from free to more or less fixed growth with increasing maturity of the plant.