Leaf Development

Abstract

The shoot system is the basic unit of development of seed plants andis composed of a leaf, a stem, and a lateral bud that differentiatesinto a lateral shoot. The most specialized organ in angiosperms,the flower, can be considered to be part of the same shoot systemsince floral organs, such as the sepal, petal, stamen, and carpel,are all modified leaves. Scales, bracts, and certain kinds of needleare also derived from leaves. Thus, an understanding of leaf developmentis critical to an understanding of shoot development. Moreover, leavesplay important roles in photosynthesis, respiration and photoperception.Thus, a full understanding of leaves is directly related to a fullunderstanding of seed plants.The details of leaf development remainunclear. The difficulties encountered in studies of leaf development,in particular in dicotyledonous plants such as Arabidopsis thaliana(L.) Henyn., are derived from the complex process of leaf development,during which the division and elongation of cells occur at the sametime and in the same region of the leaf primordium (Maksymowych,1963; Poethig and Sussex, 1985). Thus, we cannot divide the entireprocess into unit processes in accordance with the tenets of classicalanatomy.Genetic approaches in Arabidopsis, a model plant (Meyerowitzand Pruitt, 1985), have provided a powerful tool for studies of mechanismsof leaf development in dicotyledonous plants, and various aspectsof the mechanisms that control leaf development have been revealedin recent developmental and molecular genetic studies of Arabidopsis(for reviews, see Tsukaya, 1995 and 1998; Van Lijsebettens and Clarke,1998; Sinha, 1999; Van Volkenburgh, 1999; Tsukaya, 2000; Byrne etal., 2001; Dengler and Kang, 2001; Dengler and Tsukaya, 2001; Tsukaya,2001). In this review, we shall examine the information that is currentlyavailable about various mechanisms of leaf development in Arabidopsis.Vascular patterning is also an important factor in the determinationof leaf shape, and this topic is reviewed in this resource by Turner(see also Dengler and Kang, 2001). The interested reader is alsoreferred to work on the basic characterization of the vascular patterningin foliage leaves of Arabidopsis has been carried out by Candelaet al. (1999) and Semiarti et al. (2001). For terminology, see (Fig.1).