Different responses of two tobacco cultivars and their cell suspension cultures to quercinin, a novel elicitin from Phytophthora quercina

In this study we describe the response of two tobacco cultivars (Nicotiana tabacum L. cv. Bel B and Bel W3) and their cell suspension cultures to quercinin, a novel elicitin produced by the oak pathogen Phytophthora quercina. N-terminal sequencing of the purified protein proved that it belongs to the basic β-elicitins with threonine on position 13. Both tobacco leaves and cells of the cultivar Bel W3 showed hypersensitive cell death after quercinin treatment. Leaves of Bel B also developed quercinin-induced necrosis but higher concentrations of quercinin were necessary as compared to Bel W3. Also Bel B cells showed cell death induction only at the highest quercinin concentration (20 nM). In cell suspension experiments we also measured the quercinin-induced oxidative burst, which occurred in both cultivars. H2O2 production in Bel B increased with increasing quercinin concentration and was inhibited only at the highest elicitin concentration (20 nM) whereas the oxidative burst in Bel W3 was completely abolished by 5 nM quercinin. Furthermore we demonstrated that neither H2O2 nor superoxide were responsible for cell death induction since neither the inhibitor diphenyleneiodonium (DPI) nor the enzymes catalase (CAT) and superoxide dismutase (SOD) influenced the hypersensitive reaction (HR) in Bel W3 cells. Due to the different response of Bel W3 and Bel B towards the P. quercina elicitin, our system represents an interesting tool to elucidate signaling pathways in tobacco leading to hypersensitive cell death.