Dayan Franck E, Howell J'Lynn, Weidenhamer Jeffrey D
United States Department of Agriculture, Agricultural Research Service, Natural Products Utilization Research Unit, University, MS 38677, USA.
J Exp Bot. 2009;60(7):2107-17. doi: 10.1093/jxb/erp082. Epub 2009 Apr 8.
The oily droplets exuded from the root hairs of sorghum are composed of a 1:1 ratio of sorgoleone and its lipid resorcinol analogue. The production of these droplets appears to be suppressed when c. 20 microg of exudate mg(-1) root dry weight accumulates at the tip of the root hairs. However, more exudate is produced following gentle washing of the roots with water, suggesting that the biosynthesis of lipid benzoquinones and resorcinols is a dynamic process. Sorgoleone interferes with several molecular target sites, including photosynthetic electron transport, in in vitro assays. However, the in planta mechanism of action of sorgoleone remains controversial because it is not clear whether this lipid benzoquinone exuding from the roots of sorghum is taken up by roots of the receiving plants and translocated to their foliage where it must enter the chloroplast and inhibit PSII in the thylakoid membrane. Experiments designed to test the in planta mode of action of sorgoleone demonstrated that it has no effect on the photosynthesis of older plants, but inhibits photosynthesis in germinating seedlings. Sorgoleone is not translocated acropetally in older plants, but can be absorbed through the hypocotyl and cotyledonary tissues. Therefore, the mode of action of sorgoleone may be the result of inhibition of photosynthesis in young seedlings in concert with inhibition of its other molecular target sites in older plants.
高粱根毛分泌出的油滴由高粱醌及其脂质间苯二酚类似物按1:1的比例组成。当根毛尖端积累约20微克渗出物/毫克根干重时，这些油滴的产生似乎受到抑制。然而，用水轻轻冲洗根部后会产生更多的渗出物，这表明脂质苯醌和间苯二酚的生物合成是一个动态过程。在体外试验中，高粱醌会干扰几个分子靶点，包括光合电子传递。然而，高粱醌在植物体内的作用机制仍存在争议，因为尚不清楚从高粱根部渗出的这种脂质苯醌是否会被受体植物的根吸收并转运到其叶片中，在叶片中它必须进入叶绿体并抑制类囊体膜中的PSII。旨在测试高粱醌在植物体内作用方式的实验表明，它对成熟植物的光合作用没有影响，但会抑制发芽幼苗的光合作用。在成熟植物中，高粱醌不会向顶端运输，但可以通过下胚轴和子叶组织吸收。因此，高粱醌的作用方式可能是抑制幼嫩幼苗的光合作用，并与抑制成熟植物中的其他分子靶点协同作用的结果。
