Bipolaris sorokiniana

Overview & Synopsis

2.1. Detection of inducible metabolites in wheat leaves infected by B. sorokinianaB. sorokiniana conidia were inoculated to the third leaves of 3-week-old wheat seedlings. We extracted metabolites from the leaves with 80% methanol 48 h after inoculation, and subjected the extracts to HPLC analysis. As shown in Fig. 1, the accumulation of compounds 1–6 was induced in leaves inoculated with B. sorokiniana. Compounds 3–6 were collected by preparative HPLC and subjected to LC-MS analysis. 3–6 showed [M+H] + ions at m/z 251, 293, 291, and 277, respectively. Comparison of the detected ions and retention time by HPLC analysis with those of authentic compounds revealed 6 was CouAgm. LC-MS/MS analysis of 3–6 showed different fragment ions at m/z 88 in 3, m/z 130 in 4, m/z 128 in 5, and m/z 114 in 6 in addition to a commonly detected fragment ion at m/z 147 corresponding to coumaroyl moiety (Fig. S1). The fragment ion at m/z 114 in 6 corresponded to an agmatine moiety. Differences in fragment ions among 3–5 were due to the conversion of a guanidine group to amine (−42), the addition of a hydroxy group (+16), and dehydrogenation (−2) in an agmatine moiety, respectively. Accordingly, we predicted 3–5 as p -coumaric acid amides of hydroxyputrescine, hydroxyagmatine, and hydroxydehydroagmatine, respectively. The induction of these compounds was previously shown in wheat and barley. p -Coumaroyl-3-hydroxyputrescine accumulated in wheat leaves inoculated with rust fungus (Stoessl et al., 1969). p -Coumaroyl-3-hydroxyagmatine and CouAgm accumulation was induced under snow cover in wheat (Jin and Yoshida, 2000). p -Coumaroyl-3- hydroxydehydroagmatine accumulation was induced in response to powdery mildew in barley leaves (von Röpenack et al., 1998), as well as CouAgm and p -coumaroyl-3-hydroxyagmatine. Compounds 1 and 2 in the upper left inset showed [M+H] + ions at m/z 321 and m/z 305, respectively. These ions did not correspond to those of the inducible compounds previously reported in wheat.