[EN] An efficient plant regeneration protocol has been established for two hybrid clones of Populus deltoides, MC (P. x euramericana) and UNAL (P. x interamericana). The culture of internode segments on MS medium with 0.5 μM α-Napthalene acetic acid (NAA) and 4 μM N6 -Benzyladenine for 7 weeks –2 in absence of activated charcoal and 5 in its presence—gave the highest frequency of shoot regeneration (100% for MC and 82% for UNAL). Good results also were achieved using leaves as explants, but only if they remained 5 weeks in the first medium. The 100% of regenerated shoots longer than 2 cm were rooted on ½ MS medium, independently of the addition of 0.1 μM NAA. Nevertheless, shoots developed better-formed roots in NAA-free medium, which had a positive effect in the acclimatization of plants. To know the cellular processes underlying in vitro shoot organogenesis, a histological study was made in UNAL internodes. Results revealed that in vitro culture caused swelling around the cut off zones in all explants, but only those undergoing organogenesis formed proliferation centers under subepidermal cells, which lead to bud primordia. Moreover, in vivo tissues and explants with different in vitro response showed different immunolabelling patterns when they were treated with fluorescent-monoclonal antibodies against several pectin-polysaccharides of the cell wall. Results allow us to point homogalactouronan (HG) with high degree of methyl-esterification and α-1,5-L- arabinan side chains of ramnogalactouronan-I as markers for cell division and growth, and HG with low degree of methyl-esterification as a marker for bud primordia initiation.

SI