Truitt Christopher L, Wei Han-Xun, Paré Paul W
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, USA.
Plant Cell. 2004 Feb;16(2):523-32. doi: 10.1105/tpc.017723. Epub 2004 Jan 16.
Volicitin (17-hydroxylinolenoyl-l-Gln) present in the regurgitant of Spodoptera exigua (beet armyworm caterpillars) activates the emission of volatile organic compounds (VOCs) when in contact with damaged Zea mays cv Delprim (maize) leaves. VOC emissions in turn serve as a signaling defense for the plant by attracting female parasitic wasps that prey on herbivore larvae. A tritiated form of volicitin was synthesized and shown to induce volatiles in the same fashion as the biological form. [(3)H]-l-volicitin rapidly, reversibly, and saturably bound to enriched plasma membrane fractions isolated from Z. mays leaves with an apparent K(d) of 1.3 nM and a Hill coefficient of 1.07. Analog studies showed that the l-Gln and hydroxy moieties of volicitin play an important role in binding. Treatment of plants with methyl jasmonate (MeJA) increased the total binding of [(3)H]-l-volicitin to the enriched plasma membrane more than threefold, suggesting that MeJA activates transcription of the gene encoding the binding protein. S. exigua feeding also increased total binding fourfold. Cycloheximide pretreatment of plants significantly decreased binding of radiolabeled volicitin to the enriched plasma membrane. These data provide the first experimental evidence that initiation of plant defenses in response to herbivore damage can be mediated by a binding protein-ligand interaction.
甜菜夜蛾（Spodoptera exigua）（甜菜夜蛾幼虫）反刍液中的volicitin（17-羟基亚麻酰-l-谷氨酰胺）与受损的玉米品种Delprim（玉米）叶片接触时，会激活挥发性有机化合物（VOCs）的释放。VOCs的释放反过来又通过吸引捕食草食性幼虫的雌性寄生蜂，作为植物的一种信号防御机制。合成了一种氚标记形式的volicitin，并证明其能以与生物形式相同的方式诱导挥发性物质。[(3)H]-l-volicitin能快速、可逆且饱和地与从玉米叶片中分离出的富含质膜的部分结合，其表观解离常数K(d)为1.3 nM，希尔系数为1.07。类似物研究表明，volicitin的l-谷氨酰胺和羟基部分在结合中起重要作用。用茉莉酸甲酯（MeJA）处理植物，使[(3)H]-l-volicitin与富含质膜的总结合量增加了三倍多，这表明MeJA激活了编码结合蛋白的基因的转录。甜菜夜蛾取食也使总结合量增加了四倍。用环己酰亚胺预处理植物显著降低了放射性标记的volicitin与富含质膜的结合。这些数据提供了首个实验证据，表明植物对草食动物损伤做出的防御反应可由结合蛋白-配体相互作用介导。
