Vascular Patterning

Abstract

The vascular system of the plant is a network of cells thatinterconnects all major plant organs. A vast body ofliterature describes both the patterns of vasculardevelopment and a variety of experimental approaches tostudy factors controlling vascular development (forexample (Shininger, 1979; Sachs, 1981; Aloni, 1987),however the use of molecular genetic approaches usingArabidopsis is a relatively recent entry. The vast majorityof Arabidopsis references cited in this review werepublished within the last five years, and the significance ofthis work is reflected by the publication of several recentreviews on vascular development that prominently featurework on Arabidopsis (Nelson and Dengler, 1997; Berlethand Mattsson, 2000; Berleth et al., 2000; Dengler andKang, 2001; Ye, 2002).In this review, we focus on two major aspect of veinpatterning: the apical/basal pattern (found in stems androots); and the reticulate patterns (found in all broad flatorgans) (Figure 1). The vascular system is composed oftwo tissues, xylem and phloem, which function totransport water and solutes, or sugars, respectively. Eachof these tissues is composed of multiple specialized celltypes. In comparison to information gained from thezinnia in vitro system for tracheary element differentiationfrom leaf mesophyll cells (see Fukuda, 1997; Roberts andMcCann, 2000) for review), work to date usingArabidopsis has not contributed greatly to our knowledgeof vascular cell type differentiation. Consequently, only abrief description of vascular cell types is included (below)It is considered that the molecular genetic analysis ofvascular cell type differentiation is likely to be a productivearea of future work involving Arabidopsis.