JXB Advance Access published online on February 10, 2006
Journal of Experimental Botany, doi:10.1093/jxb/erj078
1 CSIC, Instituto de Agricultura Sostenible, Apdo. 4084, E-14080 Córdoba, Spain
* To whom correspondence should be addressed. 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.
Received September 19, 2005
Accepted November 29, 2005
RESEARCH PAPER
Mucilage production during the incompatible interaction between Orobanche crenata and Vicia sativa
Alejandro Pérez-de-Luque 1 *,
M. Dolores Lozano 1,
José I. Cubero 2,
Pablo González-Melendi 3,
M. Carmen Risueño 3,
and
Diego Rubiales 1
2 ETSIAM-UCO, Dep. Genética, Apdo. 3048, E-14080 Córdoba, Spain
3 CSIC, Centro de Investigaciones Biológicas, Dep. Plant Development and Nuclear Organization, Ramiro de Maeztu 9, E-28040 Madrid, Spain
Alejandro Pérez-de-Luque, E-mail: bb2pelua{at}uco.es
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