Solute fluxes from tobacco to the parasitic angiosperm Orobanche cernua and the influence of infection on host carbon and nitrogen relations.
Direct measurements of xylem sap solute concentrations and water fluxes were used, together with a modelling procedure, to calculate element fluxes within an association between O. cernua and its tobacco host. Infection of tobacco by O. cernua markedly influenced carbon acquisition and partitioning; net fixation of carbon was 20% higher in infected tobacco compared with controls. O. cernua caused an 84% increase in net carbon flux moving downward from the tobacco shoot and 73% of this carbon was intercepted by O. cernua, almost entirely through the phloem (>99%). Further, O. cernua also exerted a large impact on the nitrogen relations of the plant, notably nitrate uptake was stimulated and the amino acid content of xylem sap was lowered. O. cernua also relied heavily on host phloem for the supply of other resources, with only 5 to 15% of nitrogen and 16% of potassium, 23% of sodium, 63% of magnesium and 13% of sulphur being derived from the xylem.