Salinity effect on Cuscuta campestris Yunck. parasitism on Arabidopsis thaliana L.
Stem holoparasitic flowering plants of the genus Cuscuta are globally distributed invasive species and agricultural pests. The present research represents the combined effect of salt stress (e.g. abiotic stress) and Cuscuta campestris infection (e.g. biotic stress) on the model host plant Arabidopsis thaliana and the response of the parasite to salinity. The response of these parasites to abiotic stress conditions including salinity is poorly studied. Arabidopsis plants were continuously irrigated with 0, 50 and 150 mM NaCl and subjected to C. campestris infection. The influence of both abiotic and biotic stresses on the major osmoprotectant L-proline and three antioxidant enzymes - catalase, superoxide dismutase and guaiacol peroxidase, was assessed in both the parasite and the host plant. All four biochemical markers were differentially affected by stress, showing that the influence of C. campestris parasitism and its interaction with salinity is mostly in the site of infection (direct response) and also in roots (indirect vertical response) rather than on non-infected leaves of infected plants (indirect horizontal response). Despite its absence of soil contact, C. campestris was also significantly affected by salinity (indirect response). The mutual adaptation of the parasite-host pair to salinity slightly altered the regular response to abiotic stress of A. thaliana, but no detrimental additive effect of biotic and abiotic stress was observed.