Pyricularia

Chivukula M, Renganathan V (1995) Phenolic azo dye oxidation by laccase from Pyricularia oryzae. Appl Environ Microbiol 61 4374-4377... 

Iron toxicity is a syndrome of disorders associated with large concentrations of Fe + in the soil solution. It is only found in flooded soils. A wide range of concentrations produce the symptoms, from 1000 to only 10mgL in soils with poor nutrient status—especially of P or K—or with respiration inhibitors such as H2S. There are large differences in tolerance between rice varieties. The effects include internal damage of tissues due to excessive uptake of Fe + impaired nutrient uptake, especially of P, K, Ca and Mg and increased diseases associated with imbalanced nutrition, such as brown leaf spot (caused by Helminthospo-rium oryzae), sheath blight (caused by Rhizoctonia solani) and blast (caused by Pyricularia oryzae). 

Palmore et al. first demonstrated the use of ABTS in a biofuel cell cathode, combining it with laccase from Pyricularia oryzae ABTS was dissolved at 2 mM in oxygen-saturated 0.2 M acetate buffer, pH 4, 25 °C. With a glassy carbon working electrode, an open-circuit potential of 0.53 V vs SCE was observed, reflecting the presence of HABTS in low-pH solution. Protonation of ABTS shifts the redox potential to 0.57 V vs SCE. With negligible stirring, current densities of 100 / A/cm were achieved at an electrode potential of 0.4 V vs SCE. 

In 1990, researchers at Bristol-Myers Squibb reported the isolation of Bmy-41950 (322) from S. staurosporeus strain R10069 (ATCC 55006). This isolate showed in vitro activity against human colon cancer cells (HCT-116) (307). Two years later, Isono et al. reported the isolation of the same natural product from a different Streptomyces sp., S. platensis subsp. malvinus RK-1409 and named it RK-1409 (7-oxostaurosporine) (322) (308,309). In nature, this isolate was obtained in its optically active form [ Id + 38.3 (c 0.06, CHCI3) (309). The PKC inhibitor RK-1409 (7-oxostaurosporine) inhibited the morphological change of a human erythroleukemia cell line, K-562, induced by phorbol 12,13-dibutyrate (PDBu), and also showed a weak antimicrobial activity against Chlorella vulgaris and Pyricularia oryzae (308). 

With respect to five-membered lactones fused to hexopyranose units, some approaches have been reported so far and the exploitation of their synthetic potential has led to the access of new carbohydrate derivatives. Bicyclic derivatives of this type are key intermediates in the synthesis of the epimer at C-3 of the sugar moiety contained in miharamycins [212, 213]. The latter are antibiotics known to inhibit strongly Pyricularia oryzae, which produces the rice blast disease. These compounds are also considered to be a potential bioterrorism agent (Scheme 42). Hence, the 3,3-spiroepoxide 176 was converted into the 3-C-cyanomethyl derivative 177, the hydrolysis of which led to spontaneous cyclization in the presence of... 

OS123 Kono, Y., S. Takeuchi, O. Kodama, and T. Akatsuka. Absolute configuration of Oryzalexin A and structures of its related phytoalexins isolated from rice blast leaves infected with Pyricularia oryzae. Agr Biol Chem 1984 48(1) 253-255. 

Monosubstituted pyrrolo[2,3- ]pyridine derivatives substituted at positions 2 or 6 of the ring system, 26, exhibit antifungal activity against Pyricularia oryzae, a fungus that causes rice blast <1997JFA2345>. 

Isolated from the fungi Ceratocystis [2], Pyricularia oryzae [5], Plectophomella. 

Edifenphos, O-ethyl 5,5-diphenyl phosphorodithioate, was announced in 1968 and introduced commercially by Bayer AG for the control of rice blast, Pyricularia oryzae. Iprobenfos, 5-benzyl 0,0-diisopropyl phosphorothioate, was introduced by Kumiai Chemical... 

Melanin is a collective term for brown or black pigments. They are condensates of phenolics and are widely distributed in nature, examples of this diverse chemistry being found in animals, plants and fungi. They perform various roles but in some fungi, notably Pyricularia oryzae and Colletotrichum spp., melanin biosynthesis is an essential feature in pathogenicity, the biosynthesis of melanin in appressorial walls being a requirement for the development of infection hyphae and subsequent penetration of the host epidermis. For example, melanin-deficient mutants of P. oryzae are not pathogenic. 

Probenazole is used for the control of Pyricularia oryzae in rice (Figure 4.40). Interestingly, probenazole is ineffective against P. oryzae as a pathogen of barley, implying a dependence upon the metabolism of the natural host, rice, or a different SAR response. 

In this section, tetramic acids with an acyl group substituent at C-3 are discussed. The simplest of the naturally occurring 3-acyl tetramic acids, tenuazonic acid (6), was first isolated from the culture filtrate of Alter-naria tenuis [18] and, subsequently, from other fungal species (A. alternate, A. longipes, Pyricularia oryzae) [19,20]. Species of Altemaria are known to produce more than 70 secondary metabolites, many of which, particularly those from the Altemaria altemata complex, are mycotoxins [19]. The absolute stereochemistry of 6 (55,65) was deduced from the formation of L-isoleucine on ozonolysis followed by acid hydrolysis [21]. 

The organisms Pyricularia oryzae, which causes rice blast, and Helminthosporium oryzae, which causes brown leaf spot, can be controlled with complexes of the ligands 1-phenyl-3-methyl-4-nitroso-2-pyrazolin-5-one (36) and 3-methyl-4-nitroso-2-pyrazolin-5-one (37). The complexes were of the type ML Xj (L = 36, 37 X = C1-, Br, N03 ) or [ML2]Y2 (Y = C104 ). The former were assigned an octahedral or distorted octahedral structure and the latter are tetrahedral. The most active nickel complex was (38).92... 

The zinc analogue of complex (38) is effective against Pyricularia oryzae and Helminthosporium oryzae,92 and the zinc analogue of complex (42) is active against the latter organism.106... 

Another group of fungicides interferes with cell wall formation. Two examples of this group include 1) the polyoxines, which prevent chitin formation by competitively inhibiting chitin-synthase, the final enzyme involved in chitin biosynthesis, and 2) melanine biosynthesis inhibitors, especially in Pyricularia oryzae. Examples of... 

When we started to look for the mode of action of different EBI s, we decided to use several pathogens as test organisms. These were Pyricularia oryzae, Botrytis cinerea, Cercospora musae, Fusarium nivale, and Drechslera teres. To get rapid information about the possible antimycotic efficacy of a test compound, we also used a non-pathogenic yeast, Saccharomycopsis lipolytica. 

In the next part of our research on EBI-fungicides, we restricted ourselves to Pyricularia oryzae since from our point of view the In vitro results with that organism are representative and the test procedure is rather simple. The test chemical is applied in a suitable concentration to the culture medium which is then inoculated from an untreated pre-culture. After a 24-hour fermentation, the cells are separated from the culture filtrate by centrifugation, resuspended in a chloroform/methanol-mixture and homogenized using an ultraturrax treatment. After this extraction procedure, the sterol-conjugates are split to free sterols by a potassium-hydroxide treatment. Adsorption of the sterols to a Sep-pak column and step-wise desorption leads to a sterol fraction which can be analyzed directly by gas chromatography on a SE-30 capillary column. 

Gas chromatography of sterols from Pyricularia treated with triadimenol. 

Figure 9. Distribution of sterols in Pyricularia oryzae after application of triadimenol.

Figure 10. Biosynthetic pathway of ergosterol in Pyricularia oryzae indicating the site of inhibition by azoles and pyrimidines.

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