Subcellular Localization of Chitinase and of Its Potential Substrate in Tomato Root Tissues Infected by Fusarium oxysporum f. sp. radicis-lycopersici.

Antiserum raised against a tomato (Lycopersicon esculentum Mill.) chitinase (molecular mass of 26 kilodaltons) was used as a probe to study the subcellular localization of this enzyme in tomato root tissues infected with Fusarium oxysporum f. sp. radicis-lycopersici. A time-course experiment revealed that chitinase accumulated earlier in the incompatible interaction than in the compatible one. However, in both systems, chitinase deposition was largely correlated with pathogen distribution. The enzyme was found to accumulate in areas where host walls were in close contact with fungal cells. In contrast, the enzyme could not be detected in vacuoles and intracellular spaces. The substantial amount of chitinase found at the fungus cell surface supports the view of an antifungal activity. However, the preferential association of the enzyme with altered fungal wall areas indicates that chitinase activity is either preceded by the hydrolytic action of other enzymes such as beta-1,3-glucanases or coincides with these enzymes. The possibility that fungal glucans released through the action of beta-1,3-glucanases may act as elicitors of chitinase production is discussed.