COMPARATIVE ULTRASTRUCTURE OF LETTUCE COTYLEDONS INFECTED WITH BOTRYTIS-CINEREA AND BREMIA-LACTUCAE AND THE HISTOCHEMICAL-LOCALIZATION OF ACID-PHOSPHATASE

The ultrastructure of the compatible interactions between lettuce cotyledons and Botrytis cinerea and Bremia lactucae were compared. Infection by Botrytis cinerea was achieved, following direct penetration through the cuticle, by growth of intramural and intracellular hyphae and was associated with rapid and widespread destruction of host tissue. Using a modified Gomori lead-salt precipitation method acid phosphatase activity was localized in the modified epidermal cell wall surrounding the penetration site of B. cinerea, at various vesicular locations in infected plant cells and dispersed throughout the disorganized cytoplasm of cells at an advanced stage of necrosis. Infection by Bremia lactucae caused no apparent adverse reaction in the cytoplasm of infected plant cells and acid phosphatase activity was largely confined to those sites, such as the dictyosomes, which were typical of healthy tissue. However, intense enzyme activity was localized within the walls of intruding haustoria and with the collar of apposition material deposited by the host around the necks of these fungus structures. Acid phosphatase was also a conspicuous feature of the apposition material deposited by lettuce in response to infection by Botrytis cinerea.