Occurrence of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and a beta-glucosidase specific for its glucoside in maize seedlings

摘要

2,4-Dihydroxy-7-methoxy-1,4-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 decreased to disappear as the plants began autotrophic growth, and the glucoside to a concentration half that of the maximum. The level of DIMBOA-G was always higher than that of the aglycone. A beta-glucosidase activity which hydrolyzes DIMBOA-G to DIMBOA and glucose was detected in crude enzyme extracts from the seedlings. Lts 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 mM, whereas that for DIBOA-G, that was substantially absent in the seedlings of the cultivar studied, was 0.52 mM. 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 seedling stage of growth, and a specific glucosidase is involved in this process. [References: 15]