AUTOLYSIS AND EXTENSION OF ISOLATED WALLS FROM GROWING CUCUMBER HYPOCOTYLS

Walls isolated from cucumber hypocotyls retain autolytic activities an d the ability to extend when placed under the appropriate conditions. To test whether autolysis and extension are related, we treated the wa lls in various ways to enhance or inhibit long-term wall extension ('c reep') and measured autolysis as release of various saccharides from t he wall. Except for some non-specific inhibitors of enzymatic activity , we found no correlation between wall extension and wall autolysis. M ost notably, autolysis and extension differed strongly in their pH dep endence. We also found that exogenous cellulases and pectinases enhanc ed extension in native walls, but when applied to walls previously ina ctivated with heat or protease these enzymes caused breakage without s ustained extension. In contrast, pretreatment of walls with pectinase or cellulase, followed by boiling in methanol to inactivate the enzyme s, resulted in walls with much stronger expansin-mediated extension re sponses. Crude protein preparations from the digestive tracts of snail s enhanced extension of both native and inactivated walls, and these p reparations contained expansin-like proteins (assessed by Western blot ting). Our results indicate that the extension of isolated cucumber wa lls does not depend directly on the activity of endogenous wall-bound autolytic enzymes. The results with exogenous enzymes suggest that the hydrolysis of matrix polysaccharides may not induce wall creep by its elf, but may act synergistically with expansins to enhance wall extens ion.