Pérez-de-Luque Alejandro, Lozano M Dolores, Cubero José I, González-Melendi Pablo, Risueño M Carmen, Rubiales Diego
CSIC, Instituto de Agricultura Sostenible, Apdo. 4084, E-14080 Córdoba, Spain.
J Exp Bot. 2006;57(4):931-42. doi: 10.1093/jxb/erj078. Epub 2006 Feb 10.
Orobanche spp. (broomrapes) are holoparasites lacking in chlorophyll and totally dependent on their host for their supply of nutrients. O. crenata is a severe constraint to legumes cultivation and breeding for resistance remains as one of the best available methods of control. However, little is known about the basis of host resistance to broomrapes. It is a multicomponent event, and resistance based on hampering development and necrosis of broomrape tubercles has been reported. In the present work, the formation of mucilage and occlusion of host xylem vessels associated with the death of O. crenata tubercles were studied histologically. Samples of necrotic O. crenata tubercles established on resistant and susceptible vetch genotypes were collected. The samples were fixed, sectioned and stained using different procedures. The sections were observed at the light microscopy level, either under bright field, epi-fluorescence or confocal laser scanning microscopy. A higher proportion of necrotic tubercles was found on the resistant genotype and this was associated with a higher percentage of occluded vessels. Mucilage is composed mainly by carbohydrates (non-esterified pectins) and the presence of polyphenols was also detected. The mucilage and other substances composed by parasite secretions and host-degraded products was found to block host vessels and obstruct the parasite supply channel, being a quantitative defensive response against O. crenata in vetch, and probably also in other legumes and plants. The presence of foreign substances (i.e. parasite secretions) and host-degraded products (i.e. carbohydrates from cell walls) inside host vessels seems to activate this response and leads to xylem occlusion and further death of established Orobanche tubercles.
列当属植物（列当）是缺乏叶绿素的全寄生植物，完全依赖寄主提供养分。刺萼列当严重制约着豆类作物的种植，培育抗性品种仍是现有的最佳防治方法之一。然而，对于寄主对列当的抗性基础知之甚少。这是一个多因素事件，已有报道称存在基于阻碍列当瘤发育和坏死的抗性。在本研究中，从组织学角度研究了与刺萼列当瘤死亡相关的黏液形成及寄主木质部导管堵塞情况。采集了在抗性和感病野豌豆基因型上形成的坏死刺萼列当瘤样本。对样本进行固定、切片，并采用不同方法染色。切片在光学显微镜下观察，观察条件为明场、落射荧光或共聚焦激光扫描显微镜。在抗性基因型上发现坏死瘤的比例更高，这与堵塞导管的百分比更高有关。黏液主要由碳水化合物（非酯化果胶）组成，还检测到了多酚的存在。发现由寄生植物分泌物和寄主降解产物组成的黏液及其他物质会堵塞寄主导管，阻碍寄生植物的养分供应通道，这是野豌豆对刺萼列当的一种定量防御反应，可能在其他豆类和植物中也存在。寄主导管内异物（即寄生植物分泌物）和寄主降解产物（即细胞壁中的碳水化合物）的存在似乎激活了这种反应，导致木质部堵塞以及已形成的列当瘤进一步死亡。
