Enhanced bud regeneration in aspen (Populus tremula L.) roots cultured in liquid media

The regeneration potential of excised aspen (Populus tremula L.) roots cult ivated in liquid medium, as affected by plant growth regulators and by the position of the isolated root explant on the main root, was investigated. T he effect of various levels of benzyladenine (BA) and thidiazuron (TDZ) on bud regeneration in root explants was studied. TDZ in the medium had a mark ed effect on bud development as compared with BA, inducing a tenfold increa se in the number of buds regenerated from various root explants. TDZ enhanc ed both root and root-borne shoot biomass production but reduced further sh oot development and elongation. The position of the isolated root sections on the main root affected regeneration, the proximal sections further away from the root tip producing the highest number of buds per explant in both BA and TDZ treatments. Buds regenerated in close proximity to the site of l ateral roots in BA-treated roots, while in TDZ-treated root sections, the b uds formed all over the root regardless of the presence of lateral roots. T he buds developed from inner cortical and sub-epidermal cell layers, disrup ting the epidermis and the inner layers. Root biomass production and growth was greatly enhanced in well-aerated bioreactor culture in the presence of 4.5 x 10(-2) muM TDZ. A high number of the root-borne shoots could be root ed and converted to plantlets. However, while shoots regenerated in a mediu m with BA rooted well in a growth regulator-free medium, shoots formed in a medium with TDZ required auxin for rooting. Roots cultured in the presence of ancymidol, a gibberellin biosynthesis inhibitor, regenerated non-hyperh ydric bud clusters and hyperhydric shoots. These were separated mechanicall y, subcultured to growth and rooting medium and transplanted ex vitro resul ting in phenotypically true-to-type plantlets. The potential of liquid cult ures for aspen shoot biomass production from roots is discussed.