ABSTRACT
The antifungal activities of chitosan and oligochitosan have been used to control postharvest decay of the fruits. The effect of chitosan and oligochitosan on mycelium growth, spore germination, and mitochondrial function of Rhizopus stolonifer was evaluated in order to establish a connection between fungus development and the main organelle in charge to provide energy to the cell. The mycelium growth of R. stolonifer was significantly reduced on minimum media amended with chitosan or oligochitosan. The highest antifungal indexes were obtained on media containing chitosan or oligochitosan at 2.0 mg ml(-1). Microscopic observation showed that chitosan and oligochitosan affected the spore germination and hyphae morphology. Both polymers increased oxygen consumption of R. stolonifer. Respiratory activity was restored with NADH in permeabilized treated and untreated cells, and was inhibited with rotenone and flavones. Complex III and IV were inhibited by antimycin A and cyanide, respectively, in treated and untreated cells. Chitosan and oligochitosan increased NADH dehydrogenase activity in isolated mitochondria. However, there were not changes in the cytochrome c oxidase and ATPase activities by effect of these polymers. These results suggest that both chitosan and oligochitosan affect the development of R. stolonifer and might be implicated in the mitochondrial dysfunction.
Subject(s)
Antifungal Agents/metabolism , Chitosan/metabolism , Mitochondria/drug effects , Mitochondria/physiology , Rhizopus/drug effects , Rhizopus/growth & development , Adenosine Triphosphatases/metabolism , Culture Media/chemistry , Electron Transport Complex IV/metabolism , Microscopy , Mycelium/cytology , Mycelium/drug effects , Mycelium/growth & development , NAD/metabolism , Oxygen/metabolism , Rhizopus/cytology , Spores, Fungal/cytology , Spores, Fungal/drug effects , Spores, Fungal/growth & developmentABSTRACT
Rhizopus stolonifer (Ehrenb.:Fr.) Vuill mitochondria contain the complete system for oxidative phosphorylation, formed by the classical components of the electron transport chain (complexes I, II, III, and IV) and the F(1)F(0)-ATP synthase (complex V). Using the native gel electrophoresis, we have shown the existence of supramolecular associations of the respiratory complexes. The composition and stoichiometry of the oxidative phosphorylation complexes were similar to those found in other organisms. Additionally, two alternative routes for the oxidation of cytosolic NADH were identified: the alternative NADH dehydrogenase and the glycerol-3-phosphate shuttles. Residual respiratory activity after inhibition of complex IV by cyanide was inhibited by low concentrations of n-octyl gallate, indicating the presence of an alternative oxidase. The K(0.5) for the respiratory substrates NADH, succinate, and glycerol-3-phosphate in permeabilized cells was higher than in isolated mitochondria, suggesting that interactions of mitochondria with other cellular elements might be important for the function of this organelle.
Subject(s)
Electron Transport/physiology , Mitochondria/metabolism , Rhizopus/metabolism , Fungal Proteins/metabolism , Mitochondrial Membranes/metabolism , Oxygen/metabolismABSTRACT
Rhizopus stolonifer es el agente causal de la pudrición blanda, enfermedad poscosecha que ocasiona pérdidas económicas importantes. Se han empleado fungicidas sintéticos como el dicloran para controlar a este microorganismo, sin embargo, se ha demostrado que los fungicidas representan un riesgo para el ambiente y la salud humana. Actualmente se buscan alternativas naturales para el control de las pudriciones poscosecha. Se evaluó in vitro e in situ el efecto antifúngico del quitosano y de los aceites esenciales de canela (Cinnamomum zeylanicum), clavo (Syzygium aromaticum) y tomillo (Thymus vulgaris) y dicloran sobre Rhizopus stolonifer. Los tratamientos más efectivos para inhibir in vitro a Rhizopus stolonifer fueron obtenidos con quitosano a 10 mg mL-1, con los tres aceites esenciales probados a la concentración de 0,3 mg mL-1, las mezclas de quitosano a 10 mg mL-1 con los aceites a 0,3 mg mL-1 y el dicloran a 1 mg mL-1. Los experimentos in situ mostraron que el tratamiento individual con quitosano fue el mejor para reducir el porcentaje de infección de los frutos de tomate (Lycopersicon esculentum) inoculados con Rhizopus stolonifer y que la mezcla de quitosano con aceites esenciales no mejora la actividad antifúngica. El quitosano y el dicloran fueron los mejores tratamientos para reducir la pérdida de peso de los frutos. Los tratamientos individuales con quitosano representan una alternativa natural para controlar la pudrición blanda en frutos de tomate.
Rhizopus stolonifer is the causal agent of soft rot, postharvest disease that causes important economic losses. Synthetic fungicides such as dichloran have been used to control this microorganism; however, it has been shown that fungicides represent a risk for the environment and human health. Actually, natural alternatives are looked for the control of postharvest rotting. In vitro and in situ experiments the antifungal effect of chitosan, essential oils of cinnamon (Cinnamomum zeylanicum), clove (Syzygium aromaticum), and thyme (Thymus vulgaris) and dichloran on Rhizopus stolonifer were evaluated. The most effective treatments for in vitro inhibition of Rhizopus stolonifer were obtained by quitosano to 10 mg mL-1, with the three essential oils proved to the concentration of 0.3 mg mL-1, the mixtures chitosan to 10 mg mL-1 with the oils at 0.3 mg mL-1 and dichloran at 1 mg mL-1. In situ experiments showed that the individual treatment with chitosan was the best to reduce the infection percentage of the tomato (Lycopersicon esculentum) fruits inoculated with Rhizopus stolonifer and chitosan mixture with essential oils did not improve its antifungal activity. Chitosan and dichloran were the best treatments to reduce the weight loss of the fruits. Individual treatments with chitosan represent a natural alternative for the control of soft rot on tomato fruits.
Subject(s)
Rhizopus/enzymology , Rhizopus/pathogenicityABSTRACT
El arroz es fuente de alimento para una gran parte de la población mundial, con alto promedio de consumo anual. En este cultivo las enfermedades de origen microbiano constituyen uno de los factores que inciden en la obtención de bajos rendimientos y calidad de los granos. La piriculariosis o añublo del arroz, causada por Pyricularia grisea, es la enfermedad más importante en este cultivo en América Latina, ya que puede provocar hasta el 100% de reducción de los rendimientos. Como parte de la estrategia de agricultura sostenible, se trata de controlar estos patógenos y lograr altos rendimientos del cultivo mediante una combinación adecuada de fertilizantes químicos y productos biológicos. En este sentido, la aplicación de inoculantes bacterianos constituidos por bacterias promotoras del crecimiento vegetal (Plant Growth- Promoting Bacteria, PGPB, por sus siglas en inglés) ha constituido una alternativa ecológica que favorece la conservación del medioambiente y el ecosistema. Este trabajo tiene como objetivo abordar el estado actual y las perspectivas de uso de bacterias rizosféricas en el control de Pyricularia grisea en el cultivo del arroz, tratando algunos temas relevantes, como son las principales enfermedades que afectan al cultivo, los géneros de PGPB más utilizados para el control de las mismas y sus principales mecanismos de acción.
Rice is an important food supply for a large part of the world population and its consumption rates are very high. Microbial diseases are one of the main causes that provoke low yields and low-quality spotted grains. Although fungi, bacteria and viruses are mostly the responsible for these losses, fungal diseases strike more frequently. Among fungi, Pyricularia grisea, the blast fungus is responsible for up to 100% of reduction in yields, being the blast the most important rice disease in Latin America. To control this pathogen, a strategy of sustainable agriculture might be developed, combining accurately chemical and biological products. PGPB based bioproducts have been considered as an eco-friendly alternative, which favours environment preservation. This work was aimed to approach the current status and outlook of the use of rhizobacteria in the biocontrol of Pyricularia grisea on rice. Main diseases attacking rice, most beneficial PGPB and its mechanisms of action will be discussed too in this review.
