Influence of nitric oxide and reactive oxygen species on development of lettuce downy mildew in Lactuca spp.
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The role of nitric oxide and reactive oxygen species, molecules indispensable for plant-pathogen signalling, was studied in the Lactuca spp.-Bremia lactucae pathosystem. Using a leaf disc model the translaminar effect of various compounds affecting their metabolism was studied by light microscopy. Time course studies revealed a slowdown in the development of B. lactucae (race BL16) infection structures by rutin (scavenger of reactive nitrogen and oxygen species) and SNP (NO donor) within 48 h post inoculation, followed by a retardation of sporulation. Application of the specific NO scavenger, PTIO, accelerated penetration of B. lactucae but had no further effects on the plant-pathogen interaction. Inhibitors of NO synthase (L-NAME) and nitrate reductase (sodium tungstate) did not influence pathogen development. Our results suggest that drastic change in the NO: hydrogen peroxide ratio seems to determine the pathogen’s fate. NO synthase-like activity significantly increased early after B. lactucae challenge in resistant L. virosa. Confocal laser scanning microscopy revealed the accumulation of nitric oxide in the penetrated cells, pointing to a role in the initiation of the hypersensitive reaction. The tips of germ tubes and appressoria of B. lactucae also accumulated NO, suggesting an essential role for this molecule in penetration of the biotrophic pathogen. Additionally, temporal changes in endogenous levels of rutin and quercetin in extracts from Lactuca spp. leaves will be discussed in connection to their role as part of the antioxidative machinery that influences the plants’ susceptibility/resistance to lettuce downy mildew.
KeywordsAntioxidants Bremia lactucae Lactuca sativa Lactuca saligna Lactuca virosa Oomycete Oxidative stress Quercetin Rutin Sodium nitroprusside
- DAF-FM DA
hours post inoculation
nitric oxide synthase
reactive oxygen species
reactive nitrogen species
Authors thank Mrs. Danuše Krátká and M.A. Iveta Hnízdová for proceeding of light microscopy samples, and Dr. Brigitte Mauch-Mani (Université de Neuchâtel, Switzerland) for critical reading of the manuscript. Provision of Lactuca virosa seeds by Prof. D. A. C. Pink (Warwick HRI, Warwick University, U.K.) as well as cooperation with Olympus Czech Group (Prague, Czech Republic) is gratefully acknowledged. The work was financed by the Czech Ministry of Education, Youth and Sports (grants No. MSM 6198959215 and 2E08018).
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