THE ELICITATION OF ETHYLENE BIOSYNTHESIS BY A TRICHODERMA XYLANASE ISNOT RELATED TO THE CELL-WALL DEGRADATION ACTIVITY OF THE ENZYME

A 6-1,4-endoxylanase (EIX) isolated from Trichoderma viride elicits pl ant defense responses in certain tobacco (Nicotiana tabacum L.) cultiv ars in addition to its xylan degradation activity. It was not clear wh ether elicitation occurs by cell wall fragments released by the enzymi c activity or by the xylanase protein interacting directly with the pl ant cells. We used protoplasts isolated from tobacco leaves to test wh ether the cell wall is required for the stimulation of ethylene biosyn thesis by EIX. Protoplasts of tobacco (cv Xanthi) responded to treatme nt with the EIX, as indicated by an increased production of ethylene a nd the loss of protoplast viability. Protoplasts prepared from ethylen e-pretreated leaves produced more ethylene and had higher rates of cel l death in response to EIX than protoplasts prepared from nonethylene- treated leaves. Protoplasts of an EIX-insensitive cultivar of tobacco (Hicks) were insensitive to high concentrations of EIX. The addition o f a crude cell wall preparation to protoplasts during incubation with EIX did not enhance the induction of ethylene biosynthesis by nonsatur ating as well as saturating concentrations of EIX. These data indicate that the xylanase activity of EIX is unrelated to the elicitation of ethylene biosynthesis through the production of some cell wall fragmen t, since the protein per se appears capable of eliciting ethylene bios ynthesis in protoplasts.