The Induction of Vascular Tissues by Auxin

Abstract

The vascular tissues of the plant connect the leaves and other parts of the shoot with the roots. The vascular system is composed of two kinds of conducting tissues: the phloem, through which organic materials are transported and the xylem, which is the conduit for water and soil nutrients. Vascular development in the plant is an open type of differentiation, it continues as long as the plant grows by apical and lateral meristems. Thus, there is a continuous development of new vascular tissues that are in dynamic relationship to one another. In spite of the complexity of structure and development of the vascular tissues, there is evidence that the auxin, indole-3-acetic acid (IAA), is the main limiting and controlling factor for both phloem and xylem differentiation (1, 12, 13). This fact raises a major problem of development, which is, what are the mechanisms by which one stimulus controls the differentiation of complex patterns of phloem and xylem? However, it should be emphasized that other growth regulators may also be involved in vascular differentiation. They are beyond the scope of this article and the reader is directed to recent reviews on this topic (e.g., 19, 21).