Differential resistance among host and non-host species underlies the variable success of the hemi-parasitic plant Rhinanthus minor.
OBJECTIVE
Rhinanthus minor is a root hemiparasitic plant that attacks a wide range of host species which are severely damaged by the parasite. Rhinanthus minor also attempts unsuccessfully to form connections to a range of non-hosts which in contrast are not damaged by the parasite; however, the underlying physiological basis of these differences is not fully understood.


METHODS
Biomass of host-parasite combinations was studied, and histology, electron microscopy and FT-IR microspectroscopy were used to determine the cellular-level interactions between Rhinanthus haustoria (the parasite's connective structure) and the roots of a range of potential host species.


RESULTS
Two distinct defence responses were observed in the non-host forbs Plantago lanceolata and Leucanthemum vulgare. Firstly, L. vulgare was able to encapsulate the parasite's invading structures preventing it from gaining access to the stele. This was supported by FT-IR microspectroscopy, used to monitor lignification in response to Rhinanthus haustoria. Secondly, host cell fragmentation was observed at the interface between the parasite and P. lanceolata. Growth data confirmed the non-host status of the two forbs whilst, in contrast, grasses and a legume which were good hosts showed no evidence of defence at the host/parasite interface.


CONCLUSIONS
Variable resistance to Rhinanthus is shown for the first time to be controlled by cellular-level resistance to haustoria by either cell fragmentation or lignification at the host/parasite interface.
Cameron
Duncan D
DD
School of Biological Science (Plant and Soil Science), University of Aberdeen Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK. d.cameron@sheffield.ac.uk
Coats
Alison M
AM
Seel
Wendy E
WE
D018533:Biomass; D019684:Magnoliopsida / Q000469:parasitology* / Q000648:ultrastructure; D018517:Plant Roots / Q000469:parasitology* / Q000648:ultrastructure