Plants of the hemiparasite Odontites verna (red bartsia) benefited markedly through association with barley (Hordeum vulgare L.) or white clover (Trifolium repens L.). Benefit commenced after the establishment of haustorial connections on the roots of a host.
Compounds containing labelled carbon moved through haustoria into the hemiparasite following feeding of [14C]urea or 14C-labelled carbon dioxide to shoots of a range of host species. The reverse movement from hemiparasite to host was of a very small proportion although the hemiparasite was clearly capable of transferring assimilates from its leaves to all parts of its root system.
A bleeding sap technique was used to study the common metabolites released from the roots of Odontites, barley and white clover and to determine those organic compounds involved in transfer from each host to the hemiparasite. After a short exposure of the host shoot to 14CO2, it was possible to recover labelled amides, amino acids, organic acids and sugars in sap exuding from the cut root stumps of host and hemiparasite, and in the ethanol-soluble fractions of host roots and hemiparasite tissues. Labelled sucrose was not detected in the bleeding sap or tissues of the hemiparasite although it was the main labelled compound to be translocated to the host root. The hemiparasite root appeared to metabolize a proportion of the assimilates that it received from a host plant.
Odontites grown alone was capable of a limited rate of synthesis of amino acids in its own roots. When grown in association with a suitable host, assimilation of nitrate by roots of the hemiparasite was supplemented by absorption of amides, amino acids and other metabolites elaborated in the host. The spectra of compounds entering the hemiparasite varied greatly with the host species, these differences being reflected in the composition of the pool of soluble compounds in the mature hemiparasite.