Anatomical Changes and Immunolocalization of Cellulase during Abscission as Observed on Nitrocellulose Tissue Prints

A fundamental event in abscission is the breakdown of cell wall material in a discrete zone of cells known as the separation layer. Three dimensional images produced by viewing tissue prints of abscission zones on nitrocellulose (NC) membranes with incident illumination showed changes in the tissue integrity taking place in the separation layer as the process of abscission proceeded. The cell softening which occurs due to the dissolution of the cell wall appeared in the tissue prints as a diffuse line at the anatomical transition between the pulvinus and petiole and was easily observed on NC tissue prints of either longitudinal or serial cross-sections through abscission zones. In bean leaf abscission the dissolution of cell walls has been correlated with the appearance of a form of cellulase with an isoelectric point of pH 9.5. Antibodies specific for this enzyme were used to study the localization of 9.5 cellulase in the distal abscission zone of Phaseolus vulgaris L., cv Red Kidney after tissue printing on NC. It was found that 9.5 cellulase was localized in the separation layer but also occurred in the vascular tissue of the adjacent pulvinus. No antibody binding was observed in nonabscising tissue or preimmune controls. These results confirm previous biochemical studies and demonstrate that immunostaining of nitrocellulose tissue prints is a fast and reliable method to localize proteins or enzymes in plant tissue.