Induction Patterns of Chitinases in Yam Callus by Inoculation with Autoclaved Fusarium oxysporum, Ethylene, and Chitin and Chitosan Oligosaccharides.

Chitinase involved in plant self-defense was investigated by inoculation of yam (Dioscorea opposita Thunb) callus with autoclaved mycelia of Fusarium oxysporum Schl. f. sp. raphani Kend. et Snyd., ethylene, and chitin and chitosan oligosaccharides. The induction of chitinase was followed by measuring the enzyme activity, and the isozyme pattern was also analyzed by activity staining and immunoblotting after disc- and SDS-PAGE. Autoclaved Fusarium oxysporum induced acidic chitinases named El and E3 with MW 33, 500 in the callus, while ethylene and oligosaccharides of chitin and chitosan induced some chitinases more basic than E1 and E3, in addition to E1 and E3. These included large chitinases with MW 38, 000 and immunologically different chitinases from E1 and E3. In total, nine chitinases were induced. Isozyme patterns of chitinase induced were different among the elicitors used, although E1 and E3 were commonly induced in all cases. Oligosaccharides of chitin and chitosan showed different chain-length dependences on the induction of chitinase activity. In a series of chitin oligosaccharides, the induction time was more shortened by longer chain-length saccharide, although the highest levels of the activity were almost the same. In a series of chitosan oligosaccharides, the activity level was most induced by mono-saccharide, followed by hexa-, di-, tri-, tetra-, and hepta-saccharides, although the induction times were almost the same. In all cases, as the concentration of the elicitor increased, the induction time was shorter. The results of this study suggest that the plant cells response to various elicitors, and then produce different chitinase isozymes in a specific induction pattern.