Artificial elevation of glutathione contents in salicylic acid-deficient tobacco (Nicotiana tabacum cv. Xanthi NahG) reduces susceptibility to the powdery mildew pathogen Euoidium longipes

The effects of elevated glutathione levels on defence responses to powdery mildew (Euoidium longipes) were investigated in a salicylic acid-deficient tobacco (Nicotiana tabacum cv. Xanthi NahG) and wild-type cv. Xanthi plants, where salicylic acid (SA) contents are normal. Aqueous solutions of reduced glutathione (GSH) and its synthetic precursor R-2-oxothiazolidine-4-carboxylic acid (OTC) were injected into leaves of tobacco plants 3 h before powdery mildew inoculation. SA-deficient NahG tobacco was hyper-susceptible to E. longipes, as judged by significantly more severe powdery mildew symptoms and enhanced pathogen accumulation. Strikingly, elevation of GSH levels in SA-deficient NahG tobacco restored susceptibility to E. longipes to the extent seen in wild-type plants (i.e. enhanced basal resistance). However, expression of the SA-mediated pathogenesis-related gene (NtPR-1a) did not increase significantly in GSH or OTC-pretreated and powdery mildew-inoculated NahG tobacco, suggesting that the induction of this PR gene may not be directly involved in the defence responses induced by GSH. Our results demonstrate that artificial elevation of glutathione content can significantly reduce susceptibility to powdery mildew in SA-deficient tobacco

Occurrence of ascorbigen, a phytoalexin-like compound in non-stressed or uninfected cabbage in the primary leaf stage

Occurrence of ascorbigen (chemically bound L-ascorbic acid) was studied in extracts of different cultivars of cabbage in cotyledonic and primary leaf stages by thin-layer chromatography, UV-VIS spectroscopic and mass spectrometric measurements. The eventual presence of 1’-methylascorbigen was also studied. It has been shown that samples prepared from cotyledons did not contain ascorbigen, in contrast to the plants in primary leaf stage. 1’-methylascorbigen was not identified in the analysed plant samples. These results demonstrate that ascorbigen is already formed in the early (primary leaf stage) development stage of cabbage

Non-linearity of Plant Resistance to Pathogens Induced by N-methylated Compounds

The N-methylated resistance inducers act within two concentration ranges characterized by suppression of infection rates. Between these active ranges there is always an inactive range (5-7 decimal dilutions) characterized in general by a high rate of infection. This unique phenomenon is called the double immune response, which means a non-linear effect. If the time interval between pre-treatment and inoculation increases the active concentration values for the double immune response shift towards original higher dose values because of the continuous metabolism of methylated inducer in the host plant. The inactive range between the two active dose values remains the same. The multiple pre-treatment of plants with the inducer gives contrasting results: the active dose ranges shifted towards the original lower values. It seems that the two active concentrations of the inducer are always the same. Methylated inducers are potential formaldehyde (HCHO) generators. HCHO generates a time- and dose-dependent immunostimulating activity. HCHO (mainly in bound form) and H2O2 can interact and the singlet oxygen and excited HCHO can be formed. The singlet oxygen may participate in the oxidation of water molecules and in biological systems previously unknown oxidants including dihydrogen trioxide and ozone, can be generated. It seems that these reactive molecules-from HCHO to O3- form the biochemical basis of the double immune response of plants to pathogens