AN OAT COLEOPTILE WALL PROTEIN THAT INDUCES WALL EXTENSION IN-VITRO AND THAT IS ANTIGENICALLY RELATED TO A SIMILAR PROTEIN FROM CUCUMBER HYPOCOTYLS

Plant cell walls expand considerably during cell enlargement, but the biochemical reactions leading to wall expansion are unknown. McQueen-M ason et al. (1992, Plant Cell 4, 1425) recently identified two protein s from cucumber (Cucumis sativus L.) that induced extension in walls i solated from dicotyledons, but were relatively ineffective on grass co leoptile walls. Here we report the identification and partial characte rization of an oat (Avena sativa L.) coleoptile wall protein with simi lar properties. The oat protein has an apparent molecular mass of 29 k Da as revealed by sodium dodecyl sulfate-polyacrylamide gel eletrophor esis. Activity was optimal between pH 4.5 and 5.0, which makes it a su itable candidate for ''acid growth'' responses of plant cell walls. Th e oat protein induced extension in walls from oat coleoptiles, cucumbe r hypocotyls and pea (Pisum sativum L.) epicotyls and was specifically recognized by an antibody raised against the 29-kDa wall-extension-in ducing protein from cucumber hypocotyls. Contrary to the situation in cucumber walls, the acid-extension response in heat-inactivated oat wa lls was only partially restored by oat or cucumber wall-extension prot eins. Our results show that an antigenically conserved protein in the walls of cucumber and oat seedlings is able to mediate a form of acid- induced wall extension. This implies that dicotyledons and grasses sha re a common biochemical mechanism for at least part of acid-induced wa ll extensions, despite the significant differences in wall composition between these two classes of plants.