Suppression of arbuscular mycorrhizal colonization and nodulation in split‐root systems of alfalfa after pre‐inoculation and treatment with Nod factors

Roots of legumes establish symbiosis with arbuscular mycorrhizal fungi (AMF) and nodule‐inducing rhizobia. The existing nodules systemically suppress subsequent nodule formation in other parts of the root, a phenomenon termed autoregulation. Similarly, mycorrhizal roots reduce further AMF colonization on other parts of the root system. In this work, split‐ root systems of alfalfa (Medicago sativa) were used to study the autoregulation of symbiosis with Sinorhizobium meliloti and the mycorrhizal fungus Glomus mosseae. It is shown that nodulation systemically influences AMF root colonization and vice versa. Nodules on one half of the split‐root system suppressed subsequent AMF colonization on the other half. Conversely, root systems pre‐colonized on one side by AMF exhibited reduced nodule formation on the other side. An inhibition effect was also observed with Nod factors (lipo‐chito‐oligosaccharides). NodSm‐IV(C16:2, S) purified from S. meliloti systemically suppressed both nodule formation and AMF colonization. The application of Nod factors, however, did not influence the allocation of 14C within the split‐root system, excluding competition for carbohydrates as the regulatory mechanism. These results indicate a systemic regulatory mechanism in the rhizobial and the arbuscular mycorrhizal association, which is similar in both symbiose

Development of arbuscular mycorrhizal fungi in the presence of different patterns of Trifolium repens shoot flavonoids

We tested the effects of the flavonoid 3-methoxi-5,6,7,8-hydroxy-4'hydroxy flavone (NMHTV) isolated from shoots of non arbuscular mycorrhizal (AM) inoculated clover, and of the flavonoids 5,6,7,8-hydroxy-3-methoxy flavone (MH-1); 5,6,7,8-hydroxy-4'- hydroxy flavone (MH-2); and 5,7-hydroxy-3,4'-methoxy flavone (MH-3); isolated from AM clover (Trifolium repens) shoots, on spore germination, hyphal length, hyphal branches and the number of cluster of auxiliary cells or the number of secondary spores (Presymbiotic stage) and on the number of entry points and the percentage of AM colonized root of tomato (Lycopersicum esculentum) by the AM fungi Gigaspora rosea, Giaspora margarita, Glomus mosseae and Glomus intraradices (Symbiotic stage). Non significant effects of the flavonoids isolated from the shoot of mycorrhizal colonized clover on the presymbiotic and symbiotic stages of Gigaspora and Glomus endophytes were found. The flavonoid NMHTV isolated from non AM clover shoot, did not affect the percentage of germination of spores but significantly increased (P < 0.05) the other steps of the presymbiotic stage of Gi. margarita spores when 2 μM concentration was used. The symbiotic stage of Gi. margarita was also significantly increased when 2 μM of the flavonoid NMHTV was applied. This flavonoid had no effect on the presymbiotic development of G. mosseae, G. intraradices and Gi. rosea except when 8 μM concentration was used, which inhibited the hyphal length of Gi. rosea. These results suggest the possible implication of the flavonoid NMHTV in the susceptibility of tomato roots to the AM formation by Gi. margarita. The absence of stimulation of the AM presymbiotic and symbiotic stages in tomato by exogenous application of the newly synthesized flavonoids MH-1, MH-2, and MH-3, in clover shoots after AM colonization, indicated that the autorregulation of the AM symbiosis can be, at least partially, due to the disappearance of flavonoids in AM colonized plants that stimulated the AM symbiosis.Fil: Scervino, Jose Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Ponce, María Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Della Mónica, Ivana Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Vierheilig, Horst. Universitat Fur Bodenkultur Wien; Austria. Consejo Superior de Investigaciones Científicas. Estación Experimental del Zaidín; EspañaFil: Ocampo, Juan Antonio. Consejo Superior de Investigaciones Científicas. Estación Experimental del Zaidín; EspañaFil: Godeas, Alicia Margarita. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Alteraciones de las actividades de enzimas antioxidantes no son características generales del proceso de colonización por hongos micorrízicos arbusculares

Antioxidant system is involved in arbuscular mycorrhizal symbiosis, but its role during the colonization process is still poorly understood. To gain new insights into the role of antioxidant system during root colonization by arbuscular mycorrhizal fungi, the activities of key antioxidant enzymes were evaluated in tomato (Solanum lycopersicum L.) roots inoculated with six strains of different genera and species: two Glomus mosseae, Glomus cubense, Glomus intraradices, Glomus sp. and Acaulospora scrobiculata. Glomus cubense and A. scrobiculata strains reached the highest infectivity levels with maximum values of colonization frequency and intensity of 29-10.88% and 18-9.20%, respectively; G. mosseae strains showed an intermediate infectivity, both with 15% of colonization frequency and maximum intensities of 7.64- 7.06%, respectively; while the infectivity levels of Glomus sp. and G. intraradices strains were the lowest with colonization frequency- 13% and intensities- 5.07 and 5.41, respectively. Some activity patterns of peroxidase, superoxide dismutase, and polyphenol oxidase enzymes were not specific for early or late colonization stages neither for the colonization level and type of strain. However, a unique superoxide dismutase-band presents at early colonization and the low level of guaiacolperoxidase activity at later stages presents in all inoculated roots indicate that these antioxidant responses are independent of colonization degree and strain. Taking together, our data suggest that alterations of the antioxidant enzyme activities are not general characteristics of the colonization process by arbuscular mycorrhizal fungi, probably having the key role on those responses the specific feature of each strain rather than colonization per se.El sistema antioxidante está involucrado en la simbiosis micorrízico-arbuscular, pero su rol durante el proceso de colonización es aún escasamente comprendido. Para esclarecer el papel del sistema antioxidante durante la colonización radical por los hongos micorrízicos arbusculares, se evaluaron las actividades de enzimas antioxidantes claves en raíces de tomate (Solanum lycopersicum L.) inoculadas con seis cepas diferentes: dos Glomus mosseae, Glomus cubense, Glomus intraradices, Glomus sp. y A. scrobiculata. Las cepas G. cubense y A. scrobiculata alcanzaron los niveles de infectividad superiores con valores máximos de colonización e intensidad de 29-10,88% y 18-9,20%, respectivamente; las cepas G. mosseae mostraron una infectividad intermedia, ambas con 15% de colonización e intensidades máximas de 7,64-7,06%, respectivamente; mientras que los niveles de infectividad de las cepas Glomus sp. y G. intraradices fueron inferiores con colonización del 13% e intensidades de 5,07 y 5,41, respectivamente. Algunos patrones de actividad de las enzimas peroxidasa, superóxido dismutasa y polifenol oxidasa no resultaron específicos para los niveles y estadios de colonización, temprano o tardío, ni tipo de cepa. No obstante, la única banda de superóxido dismutasa presente en la colonización temprana y el bajo nivel de actividad guayacol-peroxidasa en estadio tardío presente en todos los tratamientos micorrizados indican que estas respuestas antioxidantes son independientes de la cepa y el grado de colonización. En conjunto, los datos sugieren que las alteraciones de las actividades enzimáticas antioxidantes no son características generales del proceso de colonización por los hongos micorrízicos arbusculares, teniendo probablemente el rol clave sobre estas respuestas las características específicas de cada cepa más que la colonización per se.Instituto de Fisiología Vegetal, Universidad Nacional de La Plat

ALTERATIONS OF THE ANTIOXIDANT ENZYME ACTIVITIES ARE NOT GENERAL CHARACTERISTICS OF THE COLONIZATION PROCESS BY ARBUSCULAR MYCORRHIZAL FUNGI

Antioxidant system is involved in arbuscular mycorrhizal symbiosis, but its role during the colonization process is still poorly understood. To gain new insights into the role of antioxidant system during root colonization by arbuscular mycorrhizal fungi, the activities of key antioxidant enzymes were evaluated in tomato ( Solanum lycopersicum L.) roots inoculated with six strains of different genera and species: two Glomus mosseae , Glomus cubense , Glomus intraradices , Glomus sp. and Acaulospora scrobiculata . Glomus cubense and A. scrobiculata strains reached the highest infectivity levels with maximum values of colonization frequency and intensity of 29-10.88% and 18-9.20%, respectively; G. mosseae strains showed an intermediate infectivity, both with 15% of colonization frequency and maximum intensities of 7.64- 7.06%, respectively; while the infectivity levels of Glomus sp. and G. intraradices strains were the lowest with colonization frequency- 13% and intensities- 5.07 and 5.41, respectively. Some activity patterns of peroxidase, superoxide dismutase, and polyphenol oxidase enzymes were not specific for early or late colonization stages neither for the colonization level and type of strain. However, a unique superoxide dismutase-band presents at early colonization and the low level of guaiacolperoxidase activity at later stages presents in all inoculated roots indicate that these antioxidant responses are independent of colonization degree and strain. Taking together, our data suggest that alterations of the antioxidant enzyme activities are not general characteristics of the colonization process by arbuscular mycorrhizal fungi, probably having the key role on those responses the specific feature of each strain rather than colonization per se

Alteraciones de las actividades de enzimas antioxidantes no son características generales del proceso de colonización por hongos micorrízicos arbusculares

Antioxidant system is involved in arbuscular mycorrhizal symbiosis, but its role during the colonization process is still poorly understood. To gain new insights into the role of antioxidant system during root colonization by arbuscular mycorrhizal fungi, the activities of key antioxidant enzymes were evaluated in tomato (Solanum lycopersicum L.) roots inoculated with six strains of different genera and species: two Glomus mosseae, Glomus cubense, Glomus intraradices, Glomus sp. and Acaulospora scrobiculata. Glomus cubense and A. scrobiculata strains reached the highest infectivity levels with maximum values of colonization frequency and intensity of 29-10.88% and 18-9.20%, respectively; G. mosseae strains showed an intermediate infectivity, both with 15% of colonization frequency and maximum intensities of 7.64- 7.06%, respectively; while the infectivity levels of Glomus sp. and G. intraradices strains were the lowest with colonization frequency- 13% and intensities- 5.07 and 5.41, respectively. Some activity patterns of peroxidase, superoxide dismutase, and polyphenol oxidase enzymes were not specific for early or late colonization stages neither for the colonization level and type of strain. However, a unique superoxide dismutase-band presents at early colonization and the low level of guaiacolperoxidase activity at later stages presents in all inoculated roots indicate that these antioxidant responses are independent of colonization degree and strain. Taking together, our data suggest that alterations of the antioxidant enzyme activities are not general characteristics of the colonization process by arbuscular mycorrhizal fungi, probably having the key role on those responses the specific feature of each strain rather than colonization per se.El sistema antioxidante está involucrado en la simbiosis micorrízico-arbuscular, pero su rol durante el proceso de colonización es aún escasamente comprendido. Para esclarecer el papel del sistema antioxidante durante la colonización radical por los hongos micorrízicos arbusculares, se evaluaron las actividades de enzimas antioxidantes claves en raíces de tomate (Solanum lycopersicum L.) inoculadas con seis cepas diferentes: dos Glomus mosseae, Glomus cubense, Glomus intraradices, Glomus sp. y A. scrobiculata. Las cepas G. cubense y A. scrobiculata alcanzaron los niveles de infectividad superiores con valores máximos de colonización e intensidad de 29-10,88% y 18-9,20%, respectivamente; las cepas G. mosseae mostraron una infectividad intermedia, ambas con 15% de colonización e intensidades máximas de 7,64-7,06%, respectivamente; mientras que los niveles de infectividad de las cepas Glomus sp. y G. intraradices fueron inferiores con colonización del 13% e intensidades de 5,07 y 5,41, respectivamente. Algunos patrones de actividad de las enzimas peroxidasa, superóxido dismutasa y polifenol oxidasa no resultaron específicos para los niveles y estadios de colonización, temprano o tardío, ni tipo de cepa. No obstante, la única banda de superóxido dismutasa presente en la colonización temprana y el bajo nivel de actividad guayacol-peroxidasa en estadio tardío presente en todos los tratamientos micorrizados indican que estas respuestas antioxidantes son independientes de la cepa y el grado de colonización. En conjunto, los datos sugieren que las alteraciones de las actividades enzimáticas antioxidantes no son características generales del proceso de colonización por los hongos micorrízicos arbusculares, teniendo probablemente el rol clave sobre estas respuestas las características específicas de cada cepa más que la colonización per se.Instituto de Fisiología Vegetal, Universidad Nacional de La Plat