Histological study of nodule morphogenesis fromCichorium intybus L. leaves cultivatedin vitro

Summary Chicory root, stem, and leaf tissues have the propensity to regenerate organogenetic nodules following a wounding treatment. Using histological methods, we described this phenomenon on leaves ofCichorium intybus L. cv. ‘Witloof’ cultivatedin vitro. Nodule morphogenesis and bud regeneration from nodules were characterized with the assistance of light and transmission microscopy techniques. Semithin and ultrathin sections of leaves and nodules were prepared from nodule induction to bud regeneration phases. Starch and inulin in differentiating tissues were histochemically detected in semithin and handmade sections. Our study demonstrates that nodules are formed in direct contact with vascular bundles of the leaves. The nodules consist of organized structures: a vascular center is surrounded by a large parenchyma, which is delimited by a periderm of multiple cork cell layers. Inside the vascular center near phloem tissues, a secretory network of articulated pseudolaticifers develops. From parenchymatous cells, in the vicinity of vascular centers, endogenous buds can be induced. In this region, several cords of vessel initials formed the vascular connection between neoformed buds and vascular centers. Simultaneously, transfer cell specialization occurs near the neoformed vascular strands. Vascular centers play a major role in this kind of organogenesis. Sugar metabolism appears to be closely related to nodule morphogenetic events.