INDUCTION OF CHITINASES, 1,3-BETA-GLUCANASES AND OTHER PATHOGENESIS-RELATED PROTEINS IN SUGAR-BEET LEAVES UPON INFECTION WITH CERCOSPORA-BETICOLA

Pathogenesis-related (PR) proteins have been studied extensively in solanaceous species such as tobacco, and only very little in other families such as Chenopodiaceae. In tobacco many of them are still of unknown biological function, while a significant proportion exhibit glycanhydrolase (chitinase, EC 3.2.1.14 and 1,3-beta-glucanase, EC 3.2.1.39) activity and, therefore, can be related to an antimicrobial defence response. In this study, the most prominent tobacco PR-proteins belonging to the 4 major serological groups were used as a reference system to investigate the induction or accumulation of PR-proteins in sugar beet (Beta vulgaris) leaves during the necrotizing infection with the fungus Cercospora beticola. A basic and an acidic protein fraction obtained by successive cation- and anion-exchange chromatographies were analyzed separately by polyacrylamide gel electrophoresis under both denaturing and non-denaturing conditions. Proteins were revealed by staining and tentatively further characterized by their enzymatic activity and/or by immunodetection with antibodies raised against known tobacco PR-proteins. Among the 19 PR-proteins detected in sugar beet, 6 were identified as chitinases of molecular mass approximately 30 kDa (2 acidic and 4 basic enzymes) and 3 as 1,3-beta-glucanases of molecular mass approximately 35 kDa (2 acidic and one basic enzymes) and found to be serologically related to the tobacco chitinases and glucanases, respectively. No sugar beet PR-protein (including the 2 most prominent of molecular mass approximately 20 kDa) was apparently serologically related to the PR-1 and thaumatin-like group of tobacco.