Origine et degrés de ploïdie des méristèmes racinaires régénérés in vitro sur des disques foliaires issus de plantes haploïdes, diploïdes et tétraploïdes de Nicotiana tabacum (variétés 'Wisconsin 38' et 'Xanthi')

Abstract

In order to define the relation existing between the ploidy levels of the regenerated root meristems and those of the initial explants in vitro cultures of foliar discs arising from tobacco plants of different kinds of ploidy levels have been performed on the gelified medium of Murashige and Skoog modified with addition of sucrose, glutamine and indoleacetic acid. Under such conditions, numerous roots were always initiated. Foliar discs were excised from two varieties of Nicotiana tabacum L., each variety possibly being under two forms: cv. Wisconsin 38: haploid (n) androgenetic plants, diploid (2n) plants arising from seeds; cv. Xanthi: diploid (2n) plants arising from seeds, tetraploid (4n) plants previously regenerated in vitro.The histological origin of the neoformed roots was established, then the DNA contents were measured by means of a microspectrophotometer. For every kind of initial explant, ploidy levels were successively examined at the level of the apical meristem of the mother plant, in the foliar explants, and in the neoformed root meristems. Regenerated roots arose from the perifascicular cells of the leaf veins, dedifferentiation being induced by the auxin. Root meristems were directly formed without any previous callus. DNA contents in the vegetative shoot apices of the mother plants revealed their haploid, diploid, or tetraploid condition, but polyploid nuclei were found in the leaves. On the contrary, ploidy levels of the regenerated root meristems were always analogous to those of the apical meristems of the mother plants. The significance of these results in regard to the determinism of adventitious rhizogenesis was discussed.