DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) is a naturally occurring hydroxamic acid, a benzoxazinoid. DIMBOA is a powerful antibiotic present in maize, wheat, rye, and related grasses,[1]
DIMBOA was first identified in maize in 1962 as the "corn sweet substance".[2]Etiolated maize seedlings have a very sweet, almost saccharin-like taste due to their high DIMBOA content.
The biosynthesis pathway from leading from maize primary metabolism to the production of DIMBOA has been fully identified.[3][4] DIMBOA is stored as an inactive precursor, DIMBOA-glucoside, which is activated by glucosidases in response to insect feeding,[1]
In maize, DIMBOA functions as natural defense against European corn borer (Ostrinia nubilalis) larvae,[5][6] beet armyworms (Spodoptera exigua),[7] corn leaf aphids (Rhopalosiphum maidis),[8] other damaging insect pests, and pathogens, including fungi and bacteria.[1][9][10] The exact level of DIMBOA varies between individual plants,[11][12] but higher concentrations are typically found in young seedlings and the concentration decreases as the plant ages.[13] Natural variation in the Bx1 gene influences the DIMBOA content of maize seedlings.[11][14] In adult maize plants, the DIMBOA concentration is low, but it is induced rapidly in response to insect feeding.[15] The methyltransferases Bx10, Bx11, and Bx12 convert DIMBOA into HDMBOA (2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one), which can be more toxic for insect herbivores.[12][7]
In addition to serving as a direct defensive compound due to its toxicity, DIMBOA can also function as a signaling molecule, leading to the accumulation of callose in response to treatment with chitosan (a fungal elicitor) and aphid feeding.[12][16]
DIMBOA can also form complexes with iron in the rhizosphere and thereby enhance maize iron supply.[17]
Specialized insect pests such as the western corn rootworm (Diabrotica virgifera virgifera) can detect complexes between DIMBOA and iron and use these complexes for host identification and foraging.[17]
^ abcNiemeyer HM (1988). "Hydroxamic acids (4-hydroxy-1,4-benzoxazin-3-ones), defence chemicals in the gramineae". Phytochemistry. 27 (11): 3349–3358. doi:10.1016/0031-9422(88)80731-3.
^Hamilton RH, Bandurski RS, Reusch WH (1962). "Isolation and characterization of a cyclic hydroxamate from Zea mays". Cereal Chemistry. 39: 107–113.
^Klun JA, Guthrie WD, Hallauer AR, Russell WA (1970). "Genetic Nature of the Concentration of 2,4-dihydroxy-7-methoxy 2H-l,4-benzoxazin- 3(4H)-one and Resistance to the European Corn Borer in a Diallel Set of Eleven Maize Inbreds1". Crop Science. 10 (1): 87–90. doi:10.2135/cropsci1970.0011183X001000010032x.
^Cambier V, Hance T, de Hoffmann E (January 2000). "Variation of DIMBOA and related compounds content in relation to the age and plant organ in maize". Phytochemistry. 53 (2): 223–9. doi:10.1016/S0031-9422(99)00498-7. PMID10680175.