Phytoalexin accumulation in sorghum: Identification of a methyl ether of luteolinidin

Abstract

A method of HPLC analysis of 3-deoxyanthocyanidins was developed which allowed the detection of these phytoalexins by plasma desorption mass spectrometry (PDMS). In addition, the times at which samples were taken were increased to 60 h post-inoculation. As a result of the changes in protocol, a new deoxyanthocyanidin was detected. The compound was isolated and purified and found by PDMS to have a molecular weight of 285. In addition to the PDMS data, bathochromic shift analyses indicated that the structure of the compound is consistent with that of a 5-methyl ether of luteolinidin. Fungitoxicity assays demonstrated that the compound is a phytoalexin as it prevented germination by, and kiled conidia of Colletotrichum sublineolum, the sorghum anthracnose pathogen, at a concentration of 3 μM. The 5- methoxyluteolinidin exhibited greater fungitoxicity than luteolinidin, a non- methoxylated phytoalexin.