Metabolism of avenanthramide phytoalexins in oats
Metabolism of avenanthramide phytoalexins in oats
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DOI：
10.1111/j.1365-313x.2004.02163.x
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发表时间：
2004-08-01
期刊：
影响因子：
7.2
通讯作者：
Iwamura, H
中科院分区：
文献类型：
--
作者：
Okazaki, Y;Isobe, T;Iwamura, H
燕麦叶会产生植物抗毒素、燕麦生物碱，以应对病原体感染或诱导子治疗。使用低分子量、部分脱乙酰基甲壳素作为诱导剂研究了燕麦生物碱的代谢。当燕麦叶段漂浮在激发子溶液上时，燕麦生物碱在溶液中积聚。将引发的燕麦叶转移到含有稳定同位素标记的燕麦生物碱的溶液中导致标记的燕麦生物碱快速减少，表明燕麦生物碱的代谢。诱导剂处理可增强减少速率，并且取决于燕麦生物碱的种类，其中燕麦生物碱 B 减少最快。使用同位素标记动力学模型测量燕麦生物碱 A 和 B 的生物合成和代谢速率。研究发现，燕麦生物碱 B 比燕麦生物碱 A 的生物合成和代谢更加活跃。放射性标记的燕麦生物碱 B 被掺入细胞壁部分，并通过碱处理释放 99% 的掺入活性。凝胶过滤表明，碱处理后可释放源自燕麦生物碱 B 的高分子量化合物。过氧化氢酶、水杨异羟肟酸和抗坏血酸钠抑制了稳定同位素标记的燕麦生物碱的减少，表明过氧化物酶参与了代谢。与此一致的是，通过激发子处理在质外体级分中诱导了接受燕麦生物碱B作为底物的过氧化物酶活性。通过用 3-氨基-9-乙基咔唑进行活性染色并结合来自激发子处理的叶子的蛋白质的等电聚焦来观察多种碱性异过氧化物酶的出现。这些发现表明积累的燕麦生物碱在燕麦叶的质外体中被诱导型异过氧化物酶进一步代谢。
Oat leaves produce phytoalexins, avenanthramides, in response to infection by pathogens or treatment with elicitors. The metabolism of avenanthramides was investigated using low molecular weight, partially deacetylated chitin as an elicitor. When oat leaf segments are floated on the elicitor solution, avenanthramides accumulate in the solution. The transfer of elicited oat leaves to solutions containing stable-isotope-labeled avenanthramides resulted in a rapid decrease in the labeled avenanthramides, suggesting the metabolism of avenanthramides. The rate of decrease was enhanced by elicitor treatment, and was dependent on the species of avenanthramides, with avenanthramide B decreasing most rapidly. The rates of biosynthesis and metabolism of avenanthramides A and B were measured using a model of isotope-labeling dynamics. Avenanthramide B was found to be more actively biosynthesized and metabolized than avenanthramide A. Radiolabeled avenanthramide B was incorporated into the cell wall fraction and 99% of incorporated activity was released by alkaline treatment. Gel filtration indicated that high-molecular-weight compounds derived from avenanthramide B were released by alkaline treatment. The decrease in stable-isotope-labeled avenanthramides was suppressed by catalase, salicylhydroxamic acid, and sodium ascorbate, suggesting the involvement of peroxidase in the metabolism. Consistent with this, peroxidase activity that accepts avenanthramide B as a substrate was induced in apoplastic fractions by elicitor treatment. The appearance of multiple basic isoperoxidases was observed by activity staining with 3-amino-9-ethylcarbazole coupled with isoelectric focusing of proteins from elicitor-treated leaves. These findings suggest that accumulated avenanthramides are further metabolized in apoplasts in oat leaves by inducible isoperoxidases.