Gramine increase associated with rapid and transient systemic resistance in barley seedlings induced by mechanical and biological stresses

Systemic acquired resistance (SAR) is one of the intriguing issues for stud ying the mechanism in signal transduction system in a whole plant. We found that SAR and increase of an antifungal compound were induced rapidly and t ransiently in barley (Hordeum vulgare L. cv. Goseshikoku) by mechanical and biological stresses. One of the major antifungal compounds was identified as an indole alkaloid, gramine (N,N-dimethyl-3-aminomethylindole), by mass spectrum and NMR analyses. Gramine is well known as a constitutive compound of barley, but it increased significantly in the primary and secondary lea ves of barley seedlings within 12 h after pruning or inoculating with the p owdery mildew fungi of barley (Blumeria graminis Esp. hordei) and wheat (B. graminis Esp. tritici). However, in the leaf detached from unwounded seedl ings or in the leaf inoculated with the barley powdery mildew fungus, grami ne did not increase at all. In the water droplets contacted with barley lea ves, the amount of leaked gramine increased dependently upon the time after the seedling was injured mechanically. We also found a tight correlation b etween gramine increase and enhancement of resistance to the barley powdery mildew fungus in barley leaves treated with an endogenous elicitor. Furthe rmore, such a systemic resistance was not observed in a barley cultivar Mor ex that lacks the biosynthetic pathway of gramine. From these results, we c onclude that gramine is the excellent marker in rapid and transient systemi c acquired resistance in barley.