Identification of polypeptides specific to rachis abscission zone cells of Sambucus nigra

Abstract

Specific polypeptides and antigenic determinants in abscission zone cells of the leaf rachis of Sambucus nigra L. (elderberry) were identified. Extracts from abscission zone tissue (OZ) and from ethylene‐treated abscission zone tissue after separation (Zone) were probed, using sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and immunological techniques, for unique peptide components absent from neighbouring non‐zone mid‐rachis tissue (MR). Ouchterlony immuno‐diffusion revealed differences in the spectrum of antigenic determinants possessed by each tissue type when challenged with antiserum raised against OZ. Immuno‐electrophoresis showed a basic polypeptide which is expressed preferentially in the abscission zone.Immune‐competition of OZ, MR and Zone extracts using immuno‐affinity column chromatography has identified polypeptides of ca 34, ca 32, and ca 28 kDa which are (up to the limits of detection) abscission‐cell specific. An antibody raised against the ca 34 kDa polypeptide recognises a peptide of ca 34 kDa present in OZ and Zone. This peptide is absent from MR.These results suggest that the specific positional differentiation of ethylene‐responsive target cells which constitute the leaf rachis abscission zone in S. nigra is accompanied by the expression of zone‐cell‐specific antigenic determinants which are not expressed by non‐target neighbouring tissue.