On the histogenesis of L1-derived tissue in the leaf - empirical investigations into the mantle structuring point

In most dicot plants, the presence of L1-derived tissue in the leaves is limited to the epidermises. This means that cell division occurs only in an anticlinal direction in the single-layered epidermises of these leaves. Therefore, the leaf is-exactly like the corpus of the apex-covered by a histogenetically independent tissue mantle. In contrast, in most monocot plants L1-derived tissue regularly forms the mesophyll of the entire leaf margin. This means that epidermal cells divide regularly in a periclinal direction in the marginal area of these leaves. Nevertheless, among monocots, plants can be found in which the L1-derived part of the leaf tissue is limited to the epidermises and among dicots there are plants in which the L1-derived leaf tissue forms the entire leaf margin. A mantle structuring point of 2.44 cell units was formally predicted. This point is decisive for the genesis of a mantle layer in the leaf margin by suppressing periclinal divisions. Here, the first results of an empirical investigation into the postulated mantle structuring point are presented. Pelargonium, Mentha, Schefflera, Alstroemeria, Chlorophytum, Commelina and Tradescantia are used to demonstrate different courses in the histogenesis of L1-derived tissue in the leaves. The chosen examples of di- and monocot plants differ phenotypically with regard to the course of histogenesis of their L1-derived tissue. However, the underlying mechanism responsible is the same in all plant examples. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.