The induction of vascular tissues by auxin

The vascular system connects the shoot organs with the roots and enables efficient long-distance transport between them. In higher plants it is composed of two kinds of conducting tissues: the phloem, through which organic materials are transported and the xylem, which is the pathway for water and soil nutrients. In angiosperms, the functional conduits of the phloem are the sieve tubes, and the most specialized conduits of the xylem are the vessels (2). Vascular development in a plant is an open type of differentiation, continuing as long as the plant grows from apical and lateral meristems. The continuous development of new vascular tissues enables regeneration of the plant and its adaptation to changes in the environment. The differentiation of vascular tissues along the plant is induced and controlled by longitudinal streams of inductive signals (4, 52).