Occurrence of 2,4-Dihydroxy-7-methoxy-l,4-benzoxazin-3-one (DIMBOA) and a ß-Glucosidase Specific for Its Glucoside in Maize Seedlings

Kenkichi Ebisui, Atsushi Ishihara, Nobuhiro Hirai and Hajime Iwamura Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan, and CREST, Japan Science and Technology Corporation (JST) Z. Naturforsch. 53c, 793-798 (1998); received April 14/May 18, 1998 Benzoxazinones, Zea mays, Gramineae, ß-Glucosidase 2,4-Dihydroxy-7-methoxy-l,4-benzoxazin-3-one (DIMBOA) and its glucoside, DIMBOA G, appeared concurrently with germination in maize (Zea mays L.), and their concentrations per fresh weight reached a maximum 24-36 hr after germination. The aglycone then de­ creased to disappear as the plants began autotrophic growth, and the glucoside to a concen­ tration half that of the maximum. The level of DIMBOA-G was always higher than that of the aglycone. A ß-glucosidase activity which hydrolyzes DIM BOA-G to DIMBOA and glu­ cose was detected in crude enzyme extracts from the seedlings. Its activity per fresh weight varied concurrently with the occurrence of DIMBOA. The purification was performed to an apparent homogeneity by cryoprecipitation followed by cation exchange chromatography and gel filtration. The K m value for DIMBOA-G was 0.07 m M , whereas that for DIBOA-G, that was substantially absent in the seedlings of the cultivar studied, was 0.52 m M . The activity on salicin and esculin was too low to be detected. The set of results suggested that free DIMBOA occurs constitutively or in a programmed manner as defense compound at a seed­ ling stage of growth, and a specific glucosidase is involved in this process.