Division of Weed Research, ARO, Newe-Ya'ar Research Center, 30095 Ramat-Yishay, Israel.
Phytochemistry. 2011 May;72(7):624-34. doi: 10.1016/j.phytochem.2011.01.037. Epub 2011 Feb 24.
The germination of the obligate root parasites of the Orobanchaceae depends on the perception of chemical stimuli from host roots. Several compounds, collectively termed strigolactones, stimulate the germination of the various Orobanche species, but do not significantly elicit germination of Orobanche cumana, a specific parasite of sunflower. Phosphate starvation markedly decreased the stimulatory activity of sunflower root exudates toward O. cumana, and fluridone - an inhibitor of the carotenoid biosynthesis pathway - did not inhibit the production of the germination stimulant in both shoots and roots of young sunflower plants, indicating that the stimulant is not a strigolactone. We identified the natural germination stimulant from sunflower root exudates by bioassay-driven purification. Its chemical structure was elucidated as the guaianolide sesquiterpene lactone dehydrocostus lactone (DCL). Low DCL concentrations effectively stimulate the germination of O. cumana seeds but not of Phelipanche aegyptiaca (syn. Orobanche aegyptiaca). DCL and other sesquiterpene lactones were found in various plant organs, but were previously not known to be exuded to the rhizosphere where they can interact with other organisms.
列当科的专性根寄生植物的萌发依赖于对宿主根释放的化学刺激的感知。一些被统称为独脚金内酯的化合物可刺激各种列当属植物的萌发，但对向日葵列当，即向日葵的特定寄生植物，却没有明显的刺激萌发作用。磷酸盐饥饿显著降低了向日葵根系分泌物对向日葵列当的刺激活性，并且氟啶酮——类胡萝卜素生物合成途径的抑制剂——在向日葵幼苗的地上部和根部都没有抑制萌发刺激物的产生，这表明该刺激物不是独脚金内酯。我们通过基于生物测定的纯化从向日葵根系分泌物中鉴定出天然的萌发刺激物。其化学结构被阐明为环阿屯醇型倍半萜内酯去氢土沉香内酯（DCL）。低浓度的 DCL 可有效刺激向日葵列当种子的萌发，但不能刺激 Phelipanche aegyptiaca（即 Orobanche aegyptiaca）种子的萌发。DCL 和其他倍半萜内酯存在于各种植物器官中，但以前并不认为它们会被分泌到根际，在那里它们可以与其他生物体相互作用。
