Department of Plant Pathology, University of Wisconsin, Madison, Wisconsin 53706.
Plant Physiol. 1978 May;61(5):796-802. doi: 10.1104/pp.61.5.796.
Cyclic hydroxamic acids present in some species of Gramineae have been reported to be important in resistance of these plants to fungi and insects. Since the nonglucosylated forms of these acids are unstable in aqueous solution, in vitro methods for the measurement of their antibiotic properties have been difficult. Kinetics of the decomposition of 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), the major hydroxamate in corn (Zea mays L.) extracts, were studied in buffered aqueous solutions from pH 5 to 7.5 at temperatures from 20 to 80 C. Kinetics were apparently first order under all conditions tested; energies of activation (24 to 28 kcal/mol) were nearly pH-independent. DIMBOA decomposed rapidly (half-life = 5.3 hours at 28 C, pH 6.75) relative to the time required for many procedures which have been used to demonstrate the biological activity of DIMBOA. The rate of disappearance of inhibitory activity of DIMBOA toward Erwinia carotovora was indistinguishable from the rate of decomposition of DIMBOA. Contrary to reports, yields of 6-methoxy-2-benzoxazolinone (MBOA) were not quantitative. Gas-liquid chromatography analytical procedures were developed for quantitation of trimethylsilyl and acetyl derivatives of MBOA. As measured by ultraviolet spectroscopy and/or gas-liquid chromatography, conversion of DIMBOA to MBOA ranged from 40 to 75% of theoretical in aqueous buffers, bacterial growth medium, and ethyl acetate extracts of corn tissue resuspended in buffer. Yields varied with temperature, pH, and constituents in the medium.
某些禾本科植物中存在的环状羟肟酸被报道对这些植物的抗真菌和抗昆虫性具有重要作用。由于这些酸的非糖基化形式在水溶液中不稳定，因此难以在体外测量它们的抗生素特性。在 pH 值为 5 至 7.5 的缓冲水溶液中，于 20 至 80°C 的温度下，研究了玉米（Zea mays L.）提取物中主要羟肟酸 2,4-二羟基-7-甲氧基-2H-1,4-苯并恶嗪-3(4H)-酮（DIMBOA）的分解动力学。在所有测试条件下，动力学显然是一级反应；活化能（24 至 28 kcal/mol）几乎与 pH 无关。DIMBOA 相对于已被用于证明 DIMBOA 生物活性的许多程序所需的时间，迅速分解（半衰期= 28°C、pH 6.75 时为 5.3 小时）。DIMBOA 对欧文氏菌（Erwinia carotovora）的抑制活性的消失速度与 DIMBOA 的分解速度相同。与报道相反，6-甲氧基-2-苯并恶唑啉酮（MBOA）的产率不是定量的。开发了用于定量 MBOA 的三甲基硅烷基和乙酰基衍生物的气相色谱分析程序。通过紫外光谱法和/或气相色谱法测量，在水溶液缓冲液、细菌生长培养基和玉米组织在缓冲液中重新悬浮的乙酸乙酯提取物中，DIMBOA 转化为 MBOA 的转化率为理论值的 40%至 75%。产率随温度、pH 值和培养基中的成分而变化。
