Relationship of cell death in plant tissue treated with a homogeneous endopectate lyase to cell wall degradation

Abstract

A homogeneous endopectate lyase (EC ef 1 lyase) from Erwinia chrysanthemi solubilized the pectic fraction in isolated potato and tobacco pith cell walls. This enzyme rapidly released unsaturated uronide from intact plant tissue, and caused both tissue maceration and cell death. The ratio of the rate of electrolyte loss from tissue (cell injury) to the rate of uronide release from tissue (cell wall breakdown) was constant when lyase concentration, tissue (substrate) concentration or temperature was varied. Both cell injury and breakdown were greatly decreased upon removal of lyase from tissue at intervals prior to death of all the cells in treated tissue. Plasmolysis of tissue protected the protoplasts from injury by EC ef 1 lyase although cell wall breakdown was not retarded. When EC ef 1 lyase was removed from wall-degraded, plasmolyzed tissue and the tissue subjected to deplasmolysis, cell death occurred immediately; all electrolytes in the tissue were lost at a rate ofequal to the rate of depletion of electrolytes from free space. Mere contact of the plasmalemma with lyase-degraded cell walls did not result in membrane damage; damage to protoplasts in lyase-treated tissue occurred only when the protoplasts were subjected to osmotic stress. The results of this study support the hypothesis that injury to cells in plant tissue treated with pectic enzymes results from a loss in the ability of enzymatically degraded cell walls to support the limiting membrane (plasmalemma) of living cells.