AUXIN DISTRIBUTION IN A TRANSVERSE ROOT SECTION

Abstract

Plants differ in the types of the root central cylinder: diarch, triarch, tetrarch, pentarch, or polyarch. The type of the symmetry is the reflection of the relative positions of xylem and phloem bundles in a cross section of the root. The mechanisms forming different types of symmetries in the central cylinder remain poorly understood. It is assumed that vasculature differentiation is triggered and controlled by plant hormone auxin (Sachs, 1969). We have developed a model that describes auxin flow through a cell layer, imitating a cross section of the vascular cylinder in a root. We have studied the stationary distributions of auxin in the cell layer depending on the model parameters. It is shown that the nonlinear processes of auxin transport regulation are responsible for the formation of asymmetric auxin distributions, which may be interpreted as the positional information for development of the diarch structure of the vascular cylinder. However, these distributions always coexist with uniform stationary distributions, not providing positional information. It is hypothesized that the most likely factor in the formation of the final auxin distribution in a root section is an appropriate geometry of the auxin flow from the shoot to the root.

Keywords

• mathematical modeling
• morphogen
• auxin
• root
• vascular tissue differentiation
• phloem
• xylem