Changes in the Activities and Polypeptide Levels of Exo- and Endoglucanases in Cell Walls during Developmental Growth of Zea mays Coleoptiles

Exo- and endoglucanases present in cereal coleoptile cell wallsare capable of mediating hydrolysis of non-cellulosic rß-(l,3)(l,4)-glucanin situ. To assess the relationship with cell elongation, glucanaseactivities and the respective polypeptide abundance were determinedas a function of Zea mays coleoptile development. Both exo-and endoglucanase activities were quite low initially, but increasedto achieve maximum levels by days 5 or 6. Western blots revealedthat the density of the protein bands increased with coleoptiledevelopment generally in correspondence to activity levels.However, in bioassays with 3 d old coleoptile segments we foundthat auxin stimulation of glucanase activities did not resultfrom increased glucanase polypeptide levels. Hence, there wasno evidence for de novo protein synthesis in excised coleoptilesin response to added auxin. While glucanase antibodies stronglyinhibited IAA-induced elongation of coleoptile segments on days2–4, these same antibodies had little effect on day 1.We conclude that glucanases contribute to auxin mediated coleoptilegrowth only during a limited developmental interval. We proposethat when elongation is dominate, the physical properties ofthe cell wall adjust in response to metabolism of cell wallrß-(l,3)(l,4)-glucans but the enhancement of suchactivity is governed by factors other than glucanase proteinlevels. (Received December 24, 1997; Accepted April 30, 1998)