Totipotence du péricycle des organes souterrains et aériens de Rorippa sylvestris. II Régénération de racines et de bourgeons à partir de feuilles détachées ou de fragments foliaires cultivés in vitro

Abstract

When detached and placed on water, leaves of Rorippa sylvestris (Brassicaceae) can rapidly initiate roots and subsequently buds at their proximal end. This ability can be modulated through in vitro culture of leaf explants with exogenous growth hormones. Indoleacetic acid enhances both rhizogenesis and caulogenesis with optimal responses at 10 mg∙L−1. Kinetin inhibits the two processes when applied at low concentration (0.05 mg∙L−1) and leads to necrosis above 0.1 mg∙L−1. When applied simultaneously or as a short pretreatment (48 h), indoleacetic acid cancels the toxic effects of kinetin and increases budding. Budding always occurs after rhizogenesis. In all the experiments, roots and buds arise from reactivation of cells belonging to the pericycle surrounding the vascular bundle and located near the protoxylem vessels. Sequential treatments applied in order to induce early morphogenetic reorientations in this totipotent layer are also presented. The double organogenetic ability of the pericycle is discussed as well as the absence of interconversion between root and shoot meristems.