Identification of methoxylchalcones produced in response to CuCl₂ treatment and pathogen infection in barley

Changes in specialized metabolites were analyzed in barley (Hordeum vulgare) leaves treated with CuCl₂ solution as an elicitor. LC-MS analysis of the CuCl₂-treated leaves showed the induced accumulation of three compounds. Among them, two were purified by silica gel and ODS column chromatography and preparative HPLC and were identified as 2',3,4,4',6'-pentamethoxychalcone and 2'-hydroxy-3,4,4',6'-tetramethoxychalcone by spectroscopic analyses. The remaining compound was determined as 12-oxo-phytodienoic acid (OPDA), a major oxylipin in plants, by comparing its spectrum and retention time from LC-MS/MS analysis with those of the authentic compound. The accumulation of these compounds was reproduced in leaves inoculated with Bipolaris sorokiniana, the causal agent of spot blotch of the Poaceae species. This inoculation increased the amounts of other oxylipins, including jasmonic acid (JA), JA-Ile, 9-oxooctadeca-10,12-dienoic acid (9-KODE), and 13-oxooctadeca-9,11-dienoic acid (13-KODE). The treatments of the barley leaves with JA and OPDA induced the accumulation of methoxylchalcones, but treatment with 9-KODE did not. These methoxylchalcones inhibited conidial germination of B. sorokiniana and Fusarium graminearum, thereby indicating that these compounds possessed antifungal activity. Consequently, they are considered to be involved in the chemical defense processes as phytoalexins in barley. Accumulation of methoxylchalcones in response to JA treatment was observed in all seven barley cultivars tested, but was not detected in other wild Hordeum species, wheat, and rice, thus indicating that their production was specific to cultivated barley.