The effect of salt stress on Arabidopsis thaliana and Phelipanche ramosa interaction S DEMIRBAS*, K E VLACHONASIOS † , O ACAR* & A KALDIS † *Biology Department, Sciences and Arts Faculty, C ß anakkale Onsekiz Mart University, C ß anakkale, Turkey, and †Department of Botany, Faculty of Sciences, School of Biology, Aristotle University of Thessaloniki, Thessaloniki, Greece Received 5 June 2013 Revised version accepted 20 June 2013 Subject Editor: Maurizio Vurro, CNR, Bari, Italy Summary Salinity and Orobanche or Phelipanche spp. infection are important crop stress factors in agricultural areas. In this study, we investigated the effect of salt stress on Phelipanche ramosa seed germination and its attachment onto Arabidopsis thaliana roots. We also evaluated the effect of both stresses on the expression of genes regulated by abiotic and biotic stresses. According to our results, high concentration of NaCl delayed P. ramosa seed germination in the presence of a strigolactone analogue (GR24). A similar pattern was observed in the presence of A. thaliana plants. Furthermore, we found that salt-treated A. thaliana seedlings were more sensitive to P. ramosa attachment compared with the untreated plants, indicating that there was a positive correlation between salt sensitivity and the ability of P. ramosa to infect A. thaliana plants. At the molecular level, a synergystic effect of both salt and P. ramosa stresses was observed on the cold-regulated (COR) gene expression profile of treated A. thaliana seedlings. Our data clarify the interaction between parasitic plants and their hosts under abiotic stress conditions. Keywords: parasitic plant, salt-induced gene expres- sion, cold-regulated genes, relative gene expression level, biotic stress, abiotic stress, cross-protection. DEMIRBAS S, VLACHONASIOS KE, ACAR O&KALDIS A (2013). The effect of salt stress on Arabidopsis thaliana and Phelipanche ramosa interaction. Weed Research 53, 452–460. Introduction Plants are sessile organisms which are always exposed to a variety of biotic and abiotic stress factors. To sur- vive, they develop mechanisms both for rapid sensing of signals from a changing environment and for trans- mitting these in specific adaptive or defensive responses (Agarwal et al., 2006). Orobanche and Phelipanche spp. (broomrapes) are obligate root parasites, completely devoid of leaves and chlorophyll, whose growth and development fully depend on their hosts for a hetero- trophic supply of resources (Joel, 2000). Phelipanche ramosa (L.) Pomel (syn. O. ramosa L.) is the most widespread and destructive of broomrape species, affecting tomato, potato and tobacco mainly in the Mediterranean region and in Mediterranean-like cli- mates (Parker, 2009). These parasitic weeds are diffi- cult to control, because they are closely associated with the host root and are hidden underground for most of their life cycle (Vurro et al., 2009). The knowledge of mechanisms involved in resis- tance against the plant parasite is important for devel- oping strategies of control. Therefore, we have chosen Arabidopsis thaliana (L.) Heynh. as a P. ramosa host model plant. Even though it is not a crop, it is able to stimulate germination and parasitism of P. ramosa, Phelipanche aegyptiaca Pomel and Orobanche minor Smith seeds (Goldwasser et al., 2002). Arabidopsis Correspondence: Dr. S Demirbas, Biology Department, Sciences and Arts Faculty, C ß anakkale Onsekiz Mart University, 17100 C ß anakkale, Turkey. Tel: (+90) 286 2180018; Fax: (+90) 286 2180533; E-mail: sefer.demirbas@gmail.com © 2013 European Weed Research Society 53, 452–460 DOI: 10.1111/wre.12041