Effects of pectin lyase from Monilinia fructigena on viability, ultrastructure and localization of acid phosphatase of cultured apple cells

Cultured apple cells leaked ions as soon as they were exposed to purified pectin lyase (PL) from Monilinia fructigena. Under standardized conditions the rate and extent of this ion efflux—and consequent cell death—was related to the PL concentration. Lyase treatment also released acid phosphatase from cells, decreasing total activity in homogenates and increasing cell permeability to phosphatase substrates. Despite greater inhibition of acid phosphatase by glutaraldehyde fixation in lyase-treated cells compared with healthy ones, the cytoplasm of injured cells contained more reaction product from Gomori-type ultrastructural localizations of the phosphatase. Severe cell injury was also indicated by pseudoplasmolysis of protoplasts, conspicuous modification of the cytoplasm and organelles, and frequent degradation of the cell walls. Less severe injury was indicated by vesiculation of. the endoplasmic reticulum and slight retraction of the plasmalemma from the walls in some areas. Walls of these cells generally appeared unaltered, and although the tonoplast and plasmalemma were less osmiophilic, their unit structure was retained. Attempts to correlate phosphatase localization, ultrastructure and injury were complicated by the range of responses exhibited by apparently similar cells treated with the same enzyme concentration. The primary causes of injury remained unidentified.