RESUMEN
The fungal pathogen Pyricularia grisea has been studied to evaluate its production of phytotoxins for the biocontrol of the buffelgrass (Cenchrus ciliaris L.) weed. A first investigation allowed to isolate several new and known phytotoxic metabolites. However, the further investigation on the organic extract obtained from the fungus liquid culture showed the presence of other metabolites possibly contributing to its phytotoxicity. Thus, four known metabolites were isolated and identified by spectroscopic (nuclear magnetic resonance [NMR] and high-resolution electrospray ionization mass spectrometry [HRESIMS]) methods as dihydropyriculol (1), epi-dihydropyriculol (2), 3-methoxy-6,8-dihydroxy-3-methyl-3,4-dihydroisocoumarin (3), and (R)-mevalonolactone (4). The absolute configuration of 1-3 was determined for the first time by a computational analysis of their electronic circular dichroism (ECD) spectra. When the isolated compounds were bioassayed at a concentration of 5 × 10-3 M in a buffelgrass coleoptile and radicle elongation test no toxicity was detected. On the contrary, compounds 1 and 3 showed a significant stimulating effect of radical elongation. Furthermore, the difference in growth stimulation between 1 and its epimer 2 highlights the tight relationship between absolute configuration and biological activity of these fungal metabolites.
Asunto(s)
Cenchrus/microbiología , Pyricularia grisea/metabolismo , Bioensayo , Espectroscopía de Resonancia Magnética con Carbono-13 , Estructura Molecular , Espectroscopía de Protones por Resonancia Magnética , Espectrometría de Masa por Ionización de Electrospray , EstereoisomerismoRESUMEN
Pyricularia grisea has been identified as a foliar pathogen on buffelgrass (Cenchrus ciliaris) in North America and was studied as a potential source of phytotoxins for buffelgrass control. Two monosubstituted hex-4-ene-2,3-diols, named pyriculins A and B, were isolated from its culture filtrate organic extract together with (10S,11S)-(-)-epipyriculol, trans-3,4-dihydro-3,4,8-trihydroxy-1(2H)-napthalenone, and (4S)-(+)-isosclerone. Pyriculins A and B were characterized by spectroscopic (essentially nuclear magnetic resonance [NMR], High-resolution electrospray ionization mass spectrometry [HRESIMS]) and chemical methods such as (4E)-1-(4-hydroxy-1,3-dihydroisobenzofuran-1-yl)hex-4-ene-2,3-diols. The relative and absolute configuration of these compounds was determined by a combination of spectroscopic (NMR, electronic circular dichroism [ECD]) and computational tools. When bioassayed in a buffelgrass coleoptile and radicle elongation test, (10S,11S)-(-)-epipyriculol proved to be the most toxic compound. Seed germination was much reduced and slowed with respect to the control and radicles failed to elongate. All five compounds delayed germination, but only (10S,11S)-(-)-epipyriculol was able to prevent radicle development of buffelgrass seedlings. It had no effect on coleoptile elongation, while the other four compounds caused significantly increased coleoptile development relative to the control.
Asunto(s)
Cenchrus/microbiología , Glicoles/química , Glicoles/metabolismo , Pyricularia grisea/metabolismo , Glicoles/toxicidad , Pyricularia grisea/fisiologíaRESUMEN
Phenylalanine ammonia lyase (PAL)-specific activity levels were measured in suspension-cultured cells of six rice cultivars following treatment with cell wall hydrolysates prepared from seven Pyricularia grisea strains. Early after elicitation, even low hydrolysate concentrations were able to induce a significant increase in enzyme levels. However, neither rice genotypes showing differential sensitivity to blast reacted differently, nor did elicitors obtained from various pathotypes induce different reactions. At a later stage, higher hydrolysate concentrations were required to trigger maximal enzyme induction. Also in this case, only slight variations were detected in suspension cultures of a given cultivar treated with different elicitors. On the contrary, highly significant differences were observed among plant genotypes. A clear relationship was evident between the mean increase in PAL activity and the overall resistance to blast at the plant level. This trait could therefore represent a useful tool in selection for increased blast tolerance.