THE DIFFERENTIATION OF EMERGENCES INTO ADVENTITIOUS SHOOTS IN PEANUT,ARACHIS-HYPOGEA (L)

In vitro regeneration of peanut may be useful in gene transfer researc h to develop transgenic peanut plants. The purpose of this study was t o determine the feasibility of developing adventitious shoots from eme rgences. Three different types of explants, viz: whole embryo, whole l eaf and hypocotyl were compared for the regeneration potential of thei r emergences. Segments of explants, including emergences in various st ages of differentiation into adventitious shoots, were studied using b rightfield and scanning electron microscopy. Emergences, multicellular structures that resemble multicellular trichomes, were observed at th e cotyledonary node, petiole base, and on the rachis of the leaf where folioles are attached. Of these sites, the greatest number of emergen ces was found at the cotyledonary node. Explants grown on a medium con taining 10 mg/l thidiazuron (TDZ) for 3 weeks exhibited progressive mo rphological changes of emergences when compared to controls. Emergence s differentiated into three types of adventitious structures with one type resembling radially concentric shoots. These adventitious shoots had an organized apex region from which flattened leaf-like appendages emerged, a central core of procambium that differentiated into vascul ar tissue, and stomates borne in the epidermal layer. The greatest ext ent of shoot differentiation occurred at the cotyledonary node. A tota l of 11% of these shoots developed roots and grew to maturity in a gre enhouse. The ability of emergences to form adventitious shoots has imp ortant implications for gene transfer research because of their superf icial origin in epidermal and subepidermal tissues that would be direc tly exposed to particle bombardment. (C) 1997 Elsevier Science Ireland Ltd.