Resistant Lactuca spp. genotypes can efficiently modulate levels of S-nitrosothiols as reactive nitrogen species derived from nitric oxide in their defence mechanism against invading biotrophic pathogens including lettuce downy mildew. S-Nitrosylation belongs to principal signalling pathways of nitric oxide in plant development and stress responses. Protein S-nitrosylation is regulated by S-nitrosoglutathione reductase (GSNOR) as a key catabolic enzyme of S-nitrosoglutathione (GSNO), the major intracellular S-nitrosothiol. GSNOR expression, level and activity were studied in leaves of selected genotypes of lettuce (Lactuca sativa) and wild Lactuca spp. during interactions with biotrophic mildews, Bremia lactucae (lettuce downy mildew), Golovinomyces cichoracearum (lettuce powdery mildew) and non-pathogen Pseudoidium neolycopersici (tomato powdery mildew) during 168 h post inoculation (hpi). GSNOR expression was increased in all genotypes both in the early phase at 6 hpi and later phase at 72 hpi, with a high increase observed in L. sativa UCDM2 responses to all three pathogens. GSNOR protein also showed two-phase increase, with highest changes in L. virosa-B. lactucae and L. sativa cv. UCDM2-G. cichoracearum pathosystems, whereas P. neolycopersici induced GSNOR protein at 72 hpi in all genotypes. Similarly, a general pattern of modulated GSNOR activities in response to biotrophic mildews involves a two-phase increase at 6 and 72 hpi. Lettuce downy mildew infection caused GSNOR activity slightly increased only in resistant L. saligna and L. virosa genotypes; however, all genotypes showed increased GSNOR activity both at 6 and 72 hpi by lettuce powdery mildew. We observed GSNOR-mediated decrease of S-nitrosothiols as a general feature of Lactuca spp. response to mildew infection, which was also confirmed by immunohistochemical detection of GSNOR and GSNO in infected plant tissues. Our results demonstrate that GSNOR is differentially modulated in interactions of susceptible and resistant Lactuca spp. genotypes with fungal mildews and uncover the role of S-nitrosylation in molecular mechanisms of plant responses to biotrophic pathogens.

• Keywords
• Bremia lactucae, Golovinomyces cichoracearum, Lettuce downy mildew, Lettuce powdery mildew, Nitric oxide, Pseudoidium neolycopersici,
• MeSH
• Aldehyde Oxidoreductases metabolism   MeSH
• Microscopy, Confocal MeSH
• Plant Diseases microbiology   MeSH
• Disease Resistance physiology   MeSH
• Oomycetes pathogenicity   MeSH
• Polymerase Chain Reaction MeSH
• Gene Expression Regulation, Plant MeSH
• S-Nitrosothiols metabolism   MeSH
• Lactuca enzymology   physiology   MeSH
• Blotting, Western MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Aldehyde Oxidoreductases MeSH
• formaldehyde dehydrogenase, glutathione-independent MeSH Browser
• S-Nitrosothiols MeSH

Protoplast cultures are remarkable examples of plant cell dedifferentiation. The state of dedifferentiation is evidenced by changes in cell morphology, genome organization, as well as by the capability of protoplasts to differentiate into multiple types of cells (depending on the type of the stimulus applied). The first change in the genome structure is connected with large-scale chromatin decondensation, affecting chromocentres involving various types of these repetitive sequences. This paper describes not only the de- and recondensation of satellite DNA type I and 5S rDNA repetitive sequences, but it also compares the recondensation level of chromatin with the levels of oxidative stress which were decreased by using an antioxidant, as well as the capabilities of the antioxidative systems within protoplasts, during the first 72 h of their culture. It is demonstrated that the treatment of protoplasts with ascorbic acid not only decreased the level of oxidative stress but also positively stimulated the expression of the ascorbate peroxidase and catalase. It also led to a greater recondensation of the chromatin (when compared to the untreated protoplasts); in addition, it supported cell proliferation. It is concluded that large-scale genome relaxation is more directly connected with oxidative stress than with large changes in the expression of genes; and further, that its recondensation is related to the start of (as well as the level of) protection by the antioxidative systems.

• MeSH
• Ascorbate Peroxidases MeSH
• Cell Nucleus enzymology   genetics   metabolism   MeSH
• Cucumis sativus enzymology   genetics   metabolism   MeSH
• Catalase genetics   metabolism   MeSH
• Microsatellite Repeats * MeSH
• Oxidative Stress * MeSH
• Peroxidases genetics   metabolism   MeSH
• Protoplasts enzymology   metabolism   MeSH
• Plant Proteins genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Ascorbate Peroxidases MeSH
• Catalase MeSH
• Peroxidases MeSH
• Plant Proteins MeSH