Peroxidase in healthy and diseased elm trees investigated by the benzidine histochemical technique

Abstract

Peroxidase activity was localized in the xylem of healthy and diseased American elm trees by the benzidine test. The activity in the cell walls resulted in a violet-brown color, while the activity in the protoplasm produced a blue reaction. The localization of the enzyme in healthy trees was much improved by impregnation of tissues with celloidin before sectioning; this procedure reduced the diffusion of peroxidase from the tissues into the incubation solution. The cambium region of both healthy and diseased trees showed a very strong peroxidase activity; such activity was also detected in ray and axial parenchyma cells. Only in infected trees was the activity found in fibers and vessels. The role of peroxidase in the pathological alteration of xylem tissues is discussed.