Behaviour of enzymatic activities and root elongation in Argiudoll soils from the Argentine Humid Pampa treated with biosolids.

The incorporation of biosolids to soil is a strategy aiming at the re-location of these materials in the environment with a useful end: soil fertilization. In this work, the response of two Argiudoll soils (one with more than 100 years of agriculture and the other, a virgin one) to biosolid incorporation was studied under laboratory conditions. To measure this response, soil enzymatic biodescriptors, such as dehydrogenase and urease activities, and tests related to plant physiology (the root elongation test) were employed. The addition of the biosolid to both soils had a stimulating effect though different on each soil according to the added dose. Adjustment of the regression line for dehydrogenase activity with root elongation was positive and statistically significant (p<0.001). Results suggest that biodescriptors employed were suitable for studying the impact of amended biosolids on different soils.

Behaviour of enzymatic activities and root elongation in Argiudoll soils from the Argentine Humid Pampa treated with biosolids / Comportamiento de actividades enzimáticas y elongación de raíces en suelos Argiudoles de la Pampa Húmeda, Argentina, tratados con biosólidos

The incorporation of biosolids to soil is a strategy aiming at the re-location of these materials in the environment with a useful end: soil fertilization. In this work, the response of two Argiudoll soils (one with more than 100 years of agriculture and the other, a virgin one) to biosolid incorporation was studied under laboratory conditions. To measure this response, soil enzymatic biodescriptors, such as dehydrogenase and urease activities, and tests related to plant physiology (the root elongation test) were employed. The addition of the biosolid to both soils had a stimulating effect though different on each soil according to the added dose. Adjustment of the regression line for dehydrogenase activity with root elongation was positive and statistically significant (p<0.001). Results suggest that biodescriptors employed were suitable for studying the impact of amended biosolids on different soils.

La incorporación de biosólidos al suelo es una estrategia que tiene como objetivo la reubicación de estos materiales en el ambiente con un fin útil, como es la fertilización del suelo. En este trabajo se estudió, en condiciones controladas de laboratorio, la respuesta de dos suelos Argiudoles (uno con más de 100 años de agricultura y otro virgen) frente a la perturbación físico-química y biótica que genera la incorporación de un biosólido. Para medir esta respuesta se emplearon dos biodescriptores edáficos (las actividades deshidrogenasa y ureasa) y un tercero referido a la fisiología vegetal, la prueba de elongación de raíces. La incorporación del biosólido en ambos suelos, en general no deprimió el funcionamiento de las actividades enzimáticas estudiadas; contrariamente, según la dosis aportada tuvo un efecto estimulante, aunque diferente, entre ambos suelos. El ajuste de la recta de regresión de la actividad deshidrogenasa con la elongación de las plántulas fue positivo y altamente significativo, lo que indica la complementaridad de ambos descriptores. Los resultados obtenidos sugieren que los biodescriptores empleados resultaron aptos para estudiar el impacto que produce la incorporación de biosólidos a suelos agrícolas.

[Pseudomonas fluorescens survival in soils with different contents of organic matter]. / Supervivencia de Pseudomonas fluorescens en suelos con diferente contenido de materia orgánica.

Pseudomonas fluorescens are plant growth promoting rhizobacteria (PGPR). The survival of this inoculated heterotrophic bacterium may be affected by soil organic matter content (SOM). To confirm this hypothesis, three strains of P. fluorescens: UP61, C7R12 y P190 (native of Balcarce, Buenos Aires) were inoculated, in laboratory conditions, into three argentine rhizospheric soils: two Argiudolls (Balcarce, and Zavalla, Santa Fe) and a Torrifluvens (Cipolletti, Río Negro) with different SOM: 7.2; 4.3; and 2.6%, respectibily. The results indicated that the all three isolates survival in general was not different. The slopes of the regression curves in Zavalla soil were very similars, while in the Balcarce soil the strains behaviour were very different. CO2 production was superior in the Balcarce than the Zavalla soil. These results suggest that the situations that affected the survival in the Balcarce soil may be associated with the presence of a larger number of functional microflora compared with Zavalla soil. The survival in the Cipolietti soil was the lowest; independently of the protective effect of the SOM in relation with the capability of survival of the inoculated bacteria, the scarcity of survival in this soil, specially after the great fall observed, is not attributable to the low SOM content, it might be related with its high electric conductivity. The UP61 had the best survival rate in all soils.

Supervivencia de Pseudomonas fluorescens en suelos con diferente contenido de materia orgánica / Pseudomonas fluorescens survival in soils with different contents of organic matter

Pseudomonas fluorescens es una bacteria PGPR (plant growth promoting rhizobacteria), heterótrofa, capaz de combatir fitopatógenos edáficos. Su supervivencia podría estar favorecida por el elevado contenido de materia orgánica del suelo (MOS). Para probarlo, se inocularon, en condiciones de laboratorio, tres cepas de P. fluorescens: UP61, C7R12, y P190 (nativa de Balcarce, Buenos Aires) en suelos rizosféricos de tomate representativos de diferentes zonas de Argentina: suelo Argiudol (Balcarce, y Zavalla, Santa Fe) y suelo Torrifluvens (Cipolletti, Río Negro) (MOS %: 7,2; 4,3 y 2,6 respectivamente). Los resultados indicaron que la supervivencia de P. fluorescens en los suelos Argiudoles fue similar; aunque las pendientes de las curvas de supervivencia en el suelo de Zavalla fueron menores que las observadas en el suelo de Balcarce. La producción de CO2 fue superior en el suelo de Balcarce que en el suelo de Zavalla (4,3 y 2,8 mmol.g-1suelo), esta diferencia podría ser explicada por la existencia de una mayor presión competitiva por parte de la microflora nativa. La supervivencia en el suelo Torrifluvens resultó mínima, lo que sería atribuible a su elevada conductividad eléctrica más que al menor contenido de MOS. La cepa UP61 presentó en todos los casos la mejor supervivencia.

Pseudomonas fluorescens are plant growth promoting rhizobacteria (PGPR). The survival of this inoculated heterotrophic bacterium may be affected by soil organic matter content (SOM). To confirm this hypothesis, three strains of P. fluorescens: UP61, C7R12 y P190 (native of Balcarce, Buenos Aires) were inoculated, in laboratory conditions, into three argentine rhizospheric soils: two Argiudolls (Balcarce, and Zavalla, Santa Fe) and a Torrifluvens (Cipolletti, Río Negro) with different SOM: 7,2; 4,3; and 2,6%, respectibily. The results indicated that the all three isolates survival in general was not different. The slopes of the regression curves in Zavalla soil were very similars, while in the Balcarce soil the strains behaviour were very different. CO2 production was superior in the Balcarce than the Zavalla soil. These results suggest that the situations that affected the survival in the Balcarce soil may be associated with the presence of a larger number of functional microflora compared with Zavalla soil. The survival in the Cipolletti soil was the lowest; independently of the protective effect of the SOM in relation with the capability of survival of the inoculated bacteria, the scarcity of survival in this soil, specially after the great fall observed, is not attributable to the low SOM content, it might be related with its high electric conductivity. The UP61 had the best survival rate in all soils.

Supervivencia de Pseudomonas fluorescens en suelos con diferente contenido de materia orgánica. / [Pseudomonas fluorescens survival in soils with different contents of organic matter]

Pseudomonas fluorescens are plant growth promoting rhizobacteria (PGPR). The survival of this inoculated heterotrophic bacterium may be affected by soil organic matter content (SOM). To confirm this hypothesis, three strains of P. fluorescens: UP61, C7R12 y P190 (native of Balcarce, Buenos Aires) were inoculated, in laboratory conditions, into three argentine rhizospheric soils: two Argiudolls (Balcarce, and Zavalla, Santa Fe) and a Torrifluvens (Cipolletti, Río Negro) with different SOM: 7.2; 4.3; and 2.6

, respectibily. The results indicated that the all three isolates survival in general was not different. The slopes of the regression curves in Zavalla soil were very similars, while in the Balcarce soil the strains behaviour were very different. CO2 production was superior in the Balcarce than the Zavalla soil. These results suggest that the situations that affected the survival in the Balcarce soil may be associated with the presence of a larger number of functional microflora compared with Zavalla soil. The survival in the Cipolietti soil was the lowest; independently of the protective effect of the SOM in relation with the capability of survival of the inoculated bacteria, the scarcity of survival in this soil, specially after the great fall observed, is not attributable to the low SOM content, it might be related with its high electric conductivity. The UP61 had the best survival rate in all soils.

Developmental genetics of gametophytic apomixis.

Some higher plants reproduce asexually by apomixis, a natural way of cloning through seeds. Apomictic plants produce progeny that are an exact genetic replica of the mother plant. The replication is achieved through changes in the female reproductive pathway such that female gametes develop without meiosis and embryos develop without fertilization. Although apomixis is a complex developmental process, genetic evidence suggests that it might be inherited as a simple mendelian trait - a paradox that could be explained by recent data derived from apomictic species and model sexual organisms. The data suggest that apomixis might rely more on a global deregulation of sexual reproductive development than on truly new functions, and molecular mechanisms for such a global deregulation can be proposed. This new understanding has direct consequences for the engineering of apomixis in sexual crop species, an application that could have an immense impact on agriculture.

Effect of Azospirillum brasilense inoculation on urease activity in soil and gamma-sterilized soil.

Azospirillum spp. is considered a PGPR (plant growth promoting rhyzobacteria) bacterium, besides this interest, there is little information about its effects on other functional microbial groups or on soil enzymes. In this paper, the impact that A. brasilense 7001 inoculation has on urease activity expression in a Typic Argiudoll was studied. Evolution of urease activity of soil and of gamma-irradiation (25 KGy) sterilized soil, and the inoculated strain survival were tested. The relation between soil urease activity and soil NH4(+)-N was also determined. In gamma-sterilized soil, urease activity of inoculated soil increased with time, showing significant differences with regard to the control soil without inoculum at day 15. In non-sterile soil, urease activity decreased during the studied period in all treatments; in inoculated soil, it showed higher or lower values than the control depending on sampling time. Azospirillum survival was important and different according to soil conditions. The negative relation between NH4(+)-N concentration and soil urease activity (r2 = 0.62) was not observed in inoculated soil. The role of the addition of autoclaved inoculum in the urease activity expression is discussed. The research proves that in both studied situations Azospirillum modified soil urease activity, and that the competition with native microorganisms and soil NH4(+)-N may affect this bacterium capacity.

Effect of Azospirillum brasilense inoculation on urease activity in soil and gamma-sterilized soil

Azospirillum spp. is considered a PGPR (plant growth promoting rhyzobacteria) bacterium, besides this interest, there is little information about its effects on other functional microbial groups or on soil enzymes. In this paper, the impact that A. brasilense 7001 inoculation has on urease activity expression in a Typic Argiudoll was studied. Evolution of urease activity of soil and of gamma-irradiation (25 KGy) sterilized soil, and the inoculated strain survival were tested. The relation between soil urease activity and soil NH4(+)-N was also determined. In gamma-sterilized soil, urease activity of inoculated soil increased with time, showing significant differences with regard to the control soil without inoculum at day 15. In non-sterile soil, urease activity decreased during the studied period in all treatments; in inoculated soil, it showed higher or lower values than the control depending on sampling time. Azospirillum survival was important and different according to soil conditions. The negative relation between NH4(+)-N concentration and soil urease activity (r2 = 0.62) was not observed in inoculated soil. The role of the addition of autoclaved inoculum in the urease activity expression is discussed. The research proves that in both studied situations Azospirillum modified soil urease activity, and that the competition with native microorganisms and soil NH4(+)-N may affect this bacterium capacity.

Effect of Azospirillum brasilense inoculation on urease activity in soil and gamma-sterilized soil.

Azospirillum spp. is considered a PGPR (plant growth promoting rhyzobacteria) bacterium, besides this interest, there is little information about its effects on other functional microbial groups or on soil enzymes. In this paper, the impact that A. brasilense 7001 inoculation has on urease activity expression in a Typic Argiudoll was studied. Evolution of urease activity of soil and of gamma-irradiation (25 KGy) sterilized soil, and the inoculated strain survival were tested. The relation between soil urease activity and soil NH4(+)-N was also determined. In gamma-sterilized soil, urease activity of inoculated soil increased with time, showing significant differences with regard to the control soil without inoculum at day 15. In non-sterile soil, urease activity decreased during the studied period in all treatments; in inoculated soil, it showed higher or lower values than the control depending on sampling time. Azospirillum survival was important and different according to soil conditions. The negative relation between NH4(+)-N concentration and soil urease activity (r2 = 0.62) was not observed in inoculated soil. The role of the addition of autoclaved inoculum in the urease activity expression is discussed. The research proves that in both studied situations Azospirillum modified soil urease activity, and that the competition with native microorganisms and soil NH4(+)-N may affect this bacterium capacity.

Mapping diplosporous apomixis in tetraploid Tripsacum: one gene or several genes?

Polyploids in Tripsacum, a wild relative of maize, reproduce through the diplosporous type of apomixis, an asexual mode of reproduction through seeds. Diplosporous apomixis involves both the failure of meiosis and the parthenogenetic development of the unreduced gametes, resulting in progenies that are exact genetic copies of the mother plant. Apomixis is believed to be controlled by one single dominant allele, responsible for the whole developmental process. Construction of a linkage map for the chromosome controlling diplosporous apomixis in Tripsacum was carried out in both tetraploid-apomictic and diploid-sexual Tripsacum species using maize restriction fragment length polymorphism (RFLP) probes. A high level of collinearity was observed between the Tripsacum chromosome carrying the control of apomixis and a duplicated segment in the maize genome. In the apomictic tetraploid, there was a strong restriction to recombination, as compared to the corresponding genomic segment in sexual plants and maize. This suggests that apomixis, although inherited as a single Mendelian allele, might really be controlled by a cluster of linked loci. The analysis also revealed the tetrasomic nature of the inheritance of the chromosomal segment controlling apomixis, which contradicts the usually accepted hypothesis of an allopolyploid origin of apomictic species. The implications of these data for the transfer of apomixis into cultivated crops are discussed, and a new approach to studying the genetics of apomixis, based on comparative mapping, is proposed.

Non-Mendelian transmission of apomixis in maize-Tripsacum hybrids caused by a transmission ratio distortion.

Apomixis is a mode of asexual reproduction through seeds. The apomictic process bypasses both meiosis and egg cell fertilization, producing offspring that are exact genetic replicas of the mother plant. In the Tripsacum agamic complex, all polyploids reproduce through the diplosporous type of apomixis, and diploids are sexual. In this paper, molecular markers linked with diplospory were used to analyse various generations of maize-Tripsacum hybrids and backcross derivatives and to derive a model for the inheritance of diplosporous reproduction. The results suggest that the gene or genes controlling apomixis in Tripsacum are linked with a segregation distorter-type system promoting the elimination of the apomixis alleles when transmitted through haploid gametes. Hence, this model offers an explanation of the relationship between apomixis and polyploidy. The evolutionary importance of this mechanism, which protects the diploid level from being invaded by apomixis, is discussed.

Allosteric regulation by Mg2+ of the vacuolar H(+)-PPase from Acer pseudoplatanus cells. Ca2+/Mg2+ interactions.

The tonoplast H(+)-PPase was previously characterized in Acer pseudoplatanus cells (Pugin et al (1991) Plant Sci 73, 23-34; Fraichard et al (1993) Plant Physiol Biochem 31, 349-359). Tonoplast vesicles were obtained from vacuoles isolated from protoplasts of A pseudoplatanus suspension cultures and used to study kinetic effects of Mg2+ and Ca2+ on PPi hydrolysis. The concentrations of ionic species (free Mg2+, free PPi, and MgPPi complexes) were calculated with apparent dissociation constants of 55.3 microM for MgPPi and 59.6 microM for CaPPi. Our results indicated that the substrate of the tonoplast PPase was a MgPPi complex and that free Mg2+ was essential for PPi hydrolysis. With fixed free Mg2+ concentrations, PPase activity showed Michaelis-Menten kinetics with respect to MgPPi. Moreover, free Mg2+ acted as an allosteric activator with a Hill coefficient of 2.4, indicating at least two Mg2+ binding sites on the enzyme. The Mg-imidodiphosphate complex was a competitive inhibitor of the substrate MgPPi but did not change significantly the allosteric activation by free Mg2+. This result confirmed the presence of Mg2+ regulatory sites. Ca2+ acted as an uncompetitive inhibitor of MgPPi hydrolysis. Furthermore, the sensitivity of the H(+)-PPase to Ca2+ increased with decrease in free Mg2+ concentration. Therefore, Ca2+ and Mg2+ may compete for a common binding site. Taken together, our results confirm that activation by free Mg2+ and inhibition by Ca2+ could be involved in the regulation of the PPase activity in vivo.

[Survival of Azospirillum in the rhizosphere of Festuca arundinacea]. / Superviviencia de Azospirillum en rizósfera de Festuca arundinacea.

In two experiments Festuca seeds (4 or 20 seeds/pot in first or second experiment respectively) were inoculated with Azospirillum strains (sp 7, mutant streptomycin resistant and G strain) in controlled laboratory conditions. Two illumination regimes were employed (197 and 274 microE. m-2.s-1, respectively). sp 7 cell number was determined during both experiments. The total number of diazotrophic bacteria was also determined on different dates. In both experiments the control pots received the same number of autoclaving bacteria. The results suggested that: (i) sp 7 number decreased in both experiments to 4 - 5% from initial number in 22 and 23 day after inoculation. This suggests that the plant density and illumination range employed did not affect the inoculum survival; (ii) the evolution of the number of different native diazotrophics strains, along the experiment, showed that this microbial number decrease in inoculated and control pots was related to the initial number.

Superviviencia de Azospirillum en rizósfera de Festuca arundinacea / Azospirillum survivial in rhizosphere of Festuca arundinacea

En dos ensayos de inoculación de plántulas de Festuca arundinacea (4 plantas/pote y 20 plantas/pote), con dos cepas de Azospirillum spp. (sp7, ATCC 29145 y cepa G) en condiciones controladas de laboratorio y con dos niveles de iluminación (197 y 274 micronE. m-2.s-1) se estudió la supervivencia de la cepa introducida sp 7 y la evolución del número de microorganismos posibles fijadores de N2 que aparecieron a lo largo del período experimental. Como controles se utilizaron plántulas inoculadas con el mismo número de células autoclavadas. Los resultados muestran que: (i) la densidade de la cepa introducida decrece en ambos ensayos en forma similar observándose a los 22-23 días entre el 4 y el 5% de la densidad inicial, lo que sugiere que las diferentes densidades de plantas e intensidad de iluminación no afectan significativamente la supervivencia del inóculo; (ii) la densidad de dizótrofos posibles totales a los 22-23 días es similar en ambos ensayos. El seguimiento de estas poblaciones realizado en uno de los ensayos sugiere que pueden existir interacciones de distinto tipo con el inóculo y con el inóculo autoclavado, que varían durante el período estudiado. El análisis de los resultados obtenidos destaca el interés de evaluar este tipo de interacciones microbianas durante la ontogenia de la planta

Superviviencia de Azospirillum en rizósfera de Festuca arundinacea / Azospirillum survivial in rhizosphere of Festuca arundinacea

En dos ensayos de inoculación de plántulas de Festuca arundinacea (4 plantas/pote y 20 plantas/pote), con dos cepas de Azospirillum spp. (sp7, ATCC 29145 y cepa G) en condiciones controladas de laboratorio y con dos niveles de iluminación (197 y 274 micronE. m-2.s-1) se estudió la supervivencia de la cepa introducida sp 7 y la evolución del número de microorganismos posibles fijadores de N2 que aparecieron a lo largo del período experimental. Como controles se utilizaron plántulas inoculadas con el mismo número de células autoclavadas. Los resultados muestran que: (i) la densidade de la cepa introducida decrece en ambos ensayos en forma similar observándose a los 22-23 días entre el 4 y el 5% de la densidad inicial, lo que sugiere que las diferentes densidades de plantas e intensidad de iluminación no afectan significativamente la supervivencia del inóculo; (ii) la densidad de dizótrofos posibles totales a los 22-23 días es similar en ambos ensayos. El seguimiento de estas poblaciones realizado en uno de los ensayos sugiere que pueden existir interacciones de distinto tipo con el inóculo y con el inóculo autoclavado, que varían durante el período estudiado. El análisis de los resultados obtenidos destaca el interés de evaluar este tipo de interacciones microbianas durante la ontogenia de la planta (AU)

Superviviencia de Azospirillum en rizósfera de Festuca arundinacea. / [Survival of Azospirillum in the rhizosphere of Festuca arundinacea]

In two experiments Festuca seeds (4 or 20 seeds/pot in first or second experiment respectively) were inoculated with Azospirillum strains (sp 7, mutant streptomycin resistant and G strain) in controlled laboratory conditions. Two illumination regimes were employed (197 and 274 microE. m-2.s-1, respectively). sp 7 cell number was determined during both experiments. The total number of diazotrophic bacteria was also determined on different dates. In both experiments the control pots received the same number of autoclaving bacteria. The results suggested that: (i) sp 7 number decreased in both experiments to 4 - 5

from initial number in 22 and 23 day after inoculation. This suggests that the plant density and illumination range employed did not affect the inoculum survival; (ii) the evolution of the number of different native diazotrophics strains, along the experiment, showed that this microbial number decrease in inoculated and control pots was related to the initial number.