van Spronsen P C, van Brussel A A, Kijne J W
Institute of Molecular Plant Sciences, Leiden University, The Netherlands.
Eur J Cell Biol. 1995 Dec;68(4):463-9.
Vicia sativa ssp. nigra plants develop the "Thick short root" (Tsr) phenotype when both (i) the roots are inoculated with the root nodule inducing bacterium Rhizobium leguminosarum biovar viciae, and (ii) the plants, including the roots, are grown in the light. Tsr roots have a reduced length, are locally twice as thick as normal roots and have an increased number of root hairs. Development of the Tsr phenotype is correlated with the presence of nod (nodulation) genes in the rhizobia. Nod factors (lipochitin oligosaccharides), products of these nod genes, can induce the Tsr phenotype in the absence of rhizobia. The Tsr phenotype can be mimicked by addition of the ethylene-releasing compound ethephon. Using several microscopical techniques, we compared roots showing the Tsr phenotype (Tsr roots) with normal roots and roots grown in the presence of the ethylene inhibitor aminoethoxyvinylglycine (AVG). The thickening of Tsr roots appeared to be caused by a swelling of the cortical cells, which corresponded with (i) a reorientation of the interphase cortical microtubules from a transverse to a longitudinal direction, (ii) general cell wall modifications, (iii) frequent absence of middle lamellae, and (iv) local maceration. The same changes could be induced by ethephon and were inhibited by AVG. This strongly suggests that the Tsr phenotype is caused by excessive ethylene production. The ethylene-related changes mentioned above are also seen during infection thread formation, but only very locally. Apparently, Vicia roots when grown in the light overrespond to Nod factors leading to overproduction of ethylene and to a non-local "ripening" process. These phenomena inhibit nodulation of the main root by preventing formation of pre-infected threads and by reducing formation of root nodule primordia. Local controlled production of ethylene, as induced by Nod factors, may, however, be an essential element of the nodulation process.
当满足以下两个条件时，黑巢菜植株会呈现出“粗短根”（Tsr）表型：（i）根部接种能诱导根瘤形成的豌豆根瘤菌蚕豆生物型；（ii）包括根部在内的植株在光照条件下生长。Tsr根长度缩短，局部粗度是正常根的两倍，且根毛数量增加。Tsr表型的形成与根瘤菌中nod（结瘤）基因的存在相关。这些nod基因的产物——结瘤因子（脂壳寡糖），在没有根瘤菌的情况下也能诱导Tsr表型。添加能释放乙烯的化合物乙烯利可模拟Tsr表型。我们运用多种显微技术，将呈现Tsr表型的根（Tsr根）与正常根以及在乙烯抑制剂氨基乙氧基乙烯基甘氨酸（AVG）存在下生长的根进行了比较。Tsr根的加粗似乎是由皮层细胞肿胀所致，这与以下情况相对应：（i）间期皮层微管从横向重新定向为纵向；（ii）细胞壁普遍发生修饰；（iii）中层常常缺失；（iv）局部组织离析。乙烯利可诱导相同的变化，而AVG能抑制这些变化。这有力地表明，Tsr表型是由乙烯过量产生引起的。上述与乙烯相关的变化在侵染线形成过程中也会出现，但仅在非常局部的区域。显然，黑巢菜根在光照下生长时对结瘤因子反应过度，导致乙烯过量产生并引发非局部的“成熟”过程。这些现象通过阻止预侵染线的形成以及减少根瘤原基的形成来抑制主根结瘤。然而，由结瘤因子诱导的局部可控乙烯产生可能是结瘤过程的一个关键要素。
