15 Leaf Development in Arabidopsis

Abstract

Leaves are determinate structures whose primary function is to produce carbohydrates required for plant growth and development. From a developmental standpoint, leaves are interesting because they display a wide range of genetically and developmentally regulated variation in shape, and because their morphological simplicity and accessibility make them an ideal system for the analysis of basic problems in plant development. Growth control, pattern formation, and cell and tissue differentiation can all be conveniently studied in the context of leaf development. Although many of these problems have yet to be addressed in Arabidopsis, this situation is changing rapidly. This is due in part to the advantages of Arabidopsis for genetic and molecular analysis, but the relatively small size of the Arabidopsis leaf is an equally important advantage of this species because it permits microscopic analysis of an entire leaf at all stages of development.

Like most plants, Arabidopsis exhibits subtle heteroblasty (first described by Röbbelen 1957), in that leaves produced at different stages of shoot development vary in their morphology (Fig. 1). At a gross level, there are two distinct leaf types: rosette leaves and bracts. Rosette leaves are produced early in development and have long petioles and broad blades. Bracts (sometimes referred to as cauline leaves) form at the basal nodes of each branch in the inflorescence and differ from rosette leaves in that they lack petioles and have narrower, more oblong blades.

There are additional morphological differences within each of these leaf types. Early rosette leaves are small and have...