Stelmach B A, Müller A, Hennig P, Gebhardt S, Schubert-Zsilavecz M, Weiler E W
Lehrstuhl für Pflanzenphysiologie, Ruhr-Universität, D-44780 Bochum, Germany.
J Biol Chem. 2001 Apr 20;276(16):12832-8. doi: 10.1074/jbc.M010743200. Epub 2001 Jan 25.
The cyclic derivative of 13(S)-hydroperoxolinolenic acid, 12-oxophytodienoic acid, serves as a signal transducer in higher plants, mediating mechanotransductory processes and plant defenses against a variety of pathogens, and also serves as a precursor for the biosynthesis of jasmonic acid, a mediator of plant herbivore defense. Biosynthesis of 12-oxophytodienoic acid from alpha-linolenic acid occurs in plastids, mainly in chloroplasts, and is thought to start with free linolenic acid liberated from membrane lipids by lipase action. In Arabidopsis thaliana, the glycerolipid fraction contains esterified 12-oxophytodienoic acid, which can be released enzymatically by sn1-specific, but not by sn2-specific, lipases. The 12-oxophytodienoyl glycerolipid fraction was isolated, purified, and characterized. Enzymatic, mass spectrometric, and NMR spectroscopic data allowed us to establish the structure of the novel oxylipin as sn1-O-(12-oxophytodienoyl)-sn2-O-(hexadecatrienoyl)-monogalactosyl diglyceride. The novel class of lipids is localized in plastids. Purified monogalactosyl diglyceride was not converted to the sn1-(12-oxophytodienoyl) derivative by the combined action of (soybean) lipoxygenase and (A. thaliana) allene oxide synthase, an enzyme ensemble that converts free alpha-linolenic acid to free 12-oxophytodienoic acid. When leaves were wounded, a significant and transient increase in the level of (12-oxophytodienoyl)-monogalactosyl diglyceride was observed. In A. thaliana, the major fraction of 12-oxophytodienoic acid occurs esterified at the sn1 position of the plastid-specific glycerolipid, monogalactosyl diglyceride.
13(S)-氢过氧化亚麻酸的环化衍生物12-氧代植物二烯酸，在高等植物中作为信号转导分子，介导机械转导过程以及植物对多种病原体的防御，并且还是茉莉酸生物合成的前体，茉莉酸是植物抵御食草动物的介质。从α-亚麻酸生物合成12-氧代植物二烯酸发生在质体中，主要是在叶绿体中，并且被认为起始于通过脂肪酶作用从膜脂中释放出的游离亚麻酸。在拟南芥中，甘油脂部分含有酯化的12-氧代植物二烯酸，其可通过sn1特异性脂肪酶而非sn2特异性脂肪酶酶促释放。分离、纯化并表征了12-氧代植物二烯酰甘油脂部分。酶学、质谱和核磁共振光谱数据使我们能够确定这种新型氧化脂质的结构为sn1-O-(12-氧代植物二烯酰)-sn2-O-(十六碳三烯酰)-单半乳糖基甘油二酯。这种新型脂质类定位于质体中。纯化的单半乳糖基甘油二酯不会通过（大豆）脂氧合酶和（拟南芥）丙二烯氧化物合酶的联合作用转化为sn1-(12-氧代植物二烯酰)衍生物，这两种酶共同作用可将游离的α-亚麻酸转化为游离的12-氧代植物二烯酸。当叶片受到损伤时，观察到(12-氧代植物二烯酰)-单半乳糖基甘油二酯水平显著且短暂升高。在拟南芥中，12-氧代植物二烯酸的主要部分以酯化形式存在于质体特异性甘油脂单半乳糖基甘油二酯的sn1位置。
