Morphogenetic sequences of the rooting process after in vitro culture or Agrobacterium rhizogenes inoculation

Abstract

After a brief review dealing with the factors inducing adventitious rhizogenesis, the morphogenetic patterns of the rooting process induced by in vitro culture or after Agrobacterium rhizogenes inoculations are described. In vitro cultures of Nicotiana tabacum, Datura innoxia and Crepis capillaris leaf explants on Murashige and Skoog's medium supplemented with sucrose and IAA or NAA have been used in order to identify the target cells for direct and indirect rooting. The structural and functional features of the prerhizogenetic cells are described and the ploidy levels of both direct and indirect root meristems are examined by means of DNA microspectrophotometry. Data on the synergistic effects between auxin, sucrose and amino acids (particularly L-ornithine) for the reactivation of the prerhizogenetic cells are also given.

Transformed roots from carrct root discs or pea epicotyls after Agrobacterium rhizogenes inoculation arise indirectly from cambium-like layers differentiated inside a previously formed callus. Numerous auxin-like symptoms at the cell level are detected after the inoculation, suggesting modifications in the endogenous contents of auxin prior to the rooting process. It is also shown that initially non-susceptible cells (fully differentiated tobacco pith) can be induced to become susceptible by in vitro treatments resulting in cell reactivation before inoculation with the bacteria. Further work is in progress to extend these observations to non-susceptible species in order to check, via the occurrence of transformed roots, their ability to react positively to foreign Ri T-DNA.