Myriam S. Zawoznik

Heavy metals effects on proteolytic system in sunflower leaves

Plant proteolytic system includes proteases, mainly localized inside the organelles, and the ubiquitin-proteasome pathway in both, the cytoplasm and the nucleus. It was recently demonstrated that under severe Cd stress sunflower (Helianthus annuus L.) proteasome activity is reduced and this results in accumulation of oxidized proteins. In order to test if under other heavy metal stresses sunflower proteolytic system undergoes similar changes, an hydroponic experiment was carried out. Ten days old sunflower plants were transferred to hydroponic culture solutions devoid (control) or containing 100 microM of AlCl(3), CoCl(2), CuCl(2), CrCl(3), HgCl(2), NiCl(2), PbCl(2) or ZnCl(2) and analyzed for protein oxidative damage and proteolytic activities. After 4 days of metal treatment, only Co(2+), Cu(2+), Hg(2+), and Ni(2+) were found to increase carbonyl groups content. Except for Al(3+) and Zn(2+), all metals tested significantly reduced all proteasome activities (chymotrypsin-like, trypsin-like and PGPH) and acid and neutral proteases activities. The effect on basic proteases was more variable. Abundance of 20S protein after metal treatments was similar to that obtained for control samples. Co(2+), Cu(2+), Hg(2+), Ni(2+), Cr(3+), and Pb(2+) induced accumulation of ubiquitin conjugated proteins. It is concluded that heavy metal effects on proteolytic system cannot be generalized; however, impairment of proteasome functionality and decreased proteases activities seem to be a common feature involved in metal toxicity to plants.

Effect of co-inoculation with Bradyrhizobium japonicum and Azospirillum brasilense on soybean plants

Abstract In order to assess the effects of co-inoculation with both Bradyrhizobium japonicum and Azospirillum brasilense on soybean plants, a pot experiment under growth controlled conditions was carried out. Four-week-old plants were harvested and analyzed for shoot, root and nodule dry weight, nitrogen content, nodule number and distribution, nodule protein and leghaemoglobin content, and nitrogenase and glutamine synthetase activities. Nodule number and nodule dry weight were not affected by dual inoculation; however, co-inoculated plants showed a significantly higher proportion of nodules attached to the main root and located in the upper 3 cm of the root system. Although no significant difference in total dry matter production could be detected, nitrogen content of dual inoculated plants was significantly increased (23 % over B. japonicum-single. inoculated plants). Accordingly, a strong stimulation of acetylene reduction activity was observed for this treatment. Likewise, leghaemoglobin content significantly increased (39 %). These results suggest that co-inoculation with B. japonicum and A. brasilense leads to an increased number of the most active nodules, therefore, to a greater nitrogen fixation and assimilation. In addition, an enhancement of nodule effectiveness due to A. brasilense presence in the root system is suggested.

Wheat seeds harbour bacterial endophytes with potential as plant growth promoters and biocontrol agents of Fusarium graminearum

The role of endophytic communities of seeds is still poorly characterised. The purpose of this work was to survey the presence of bacterial endophytes in the seeds of a commercial wheat cultivar widely sown in Argentina and to look for plant growth promotion features and biocontrol abilities against Fusarium graminearum among them. Six isolates were obtained from wheat seeds following a culture-dependent protocol. Four isolates were assignated to Paenibacillus genus according to their 16S rRNA sequencing. The only gammaproteobacteria isolated, presumably an Enterobactereaceae of Pantoea genus, was particularly active as IAA and siderophore producer, and also solubilised phosphate and was the only one that grew on N-free medium. Several of these isolates demonstrated ability to restrain F. graminearum growth on dual culture and in a bioassay using barley and wheat kernels. An outstanding ability to form biofilm on an inert surface was corroborated for those Paenibacillus which displayed greater biocontrol of F. graminearum, and the inoculation with one of these isolates in combination with the Pantoea isolate resulted in greater chlorophyll content in barley seedlings. Our results show a significant ecological potential of some components of the wheat seed endophytic community.

Search for endophytic diazotrophs in barley seeds

Eight endophytic isolates assigned to Pseudomonas, Azospirillum, and Bacillus genera according to pheno-genotypic features were retrieved from barley seeds under selective pressure for nitrogen-fixers. Genetic relationships among related isolates were investigated through RAPD. Six isolates displayed nitrogen-fixing ability, while all could biosynthesize indolacetic acid in vitro and showed no antibiosis effects against Azospirillum brasilense Az39, a recognized PGPR.

La comunicación científica y la práctica social de la escritura

Sabemos que nuestro desarrollo académico depende, en gran medida, de acreditar una buena productividad científica. En otras palabras, de tener publicaciones. Por eso, quienes nos movemos en el mundo de la investigación científica necesitamos generar conocimiento y publicarlo. Pero antes de poder ver la luz, nuestros escritos pasarán por la mirada crítica de un comité de expertos, quienes juzgarán la calidad de nuestro trabajo a partir de lo que nosotros mismos expongamos en esos textos. Por esta sencilla razón es importante no solo qué hacemos, sino cómo lo decimos. Hoy en día llegan a las revistas especializadas una enorme cantidad de trabajos, por lo que los editores se encuentran en la necesidad de seleccionar. Y lógicamente, a la hora de elegir, elegirán lo mejor, que no solo está dado por la investigación en sí misma, sino por el modo en que es transmitida. Con esto quiero decir que no alcanza con haber hecho un trabajo interesante, novedoso y de rigor científico, y haberlo escrito sin errores de ortografía. Esas son condiciones necesarias, pero no suficientes. También hay que ser capaz de comunicarlo de manera clara, simple, breve y amena, para que el editor considere que la publicación de ese artículo en su revista bien vale la pena. ¿Hay algo que uno pueda hacer desde la redacción para lograr eso? Decididamente, mi respuesta es «sí».

Improvement of soybean grain nutritional quality under foliar inoculation with Azospirillum brasilense strain Az39

Legumes depend on biological nitrogen fixation through symbiosis with rhizobia to meet their nitrogen requirements. Certain plant growth promoting rizobacteria such as Azospirillum may cooperate in the establishment and maintenance of effective legume-rhizobia symbiosis. The aim of this work was to assess if foliar inoculation of soybean with Azospirillum brasilense Az39 has advantages over inoculation with this bacterium at sowing in combination with Bradyrhizobium japonicum E109 inoculation. To test this, glasshouse and field experiments were carried out. Higher shoot biomass was observed at V6 and R2 stages under foliar inoculation of A. brasilense Az39 as compared to coinoculation at sowing. Additionally, increased root dry biomass and higher nodule number and nodule fresh weight per plant were found at V6. Leghemoglobin levels in nodules were significantly greater in foliar-inoculated plants at both stages (V6 and R2) as compared with seed-inoculated plants. In line with these positive effects of foliar inoculation with A. brasilense Az39 on soybean growth and nodulation, grains harvested from foliar-inoculated plants had higher nitrogen and protein contents than those harvested from plants coinoculated at sowing. This was corroborated for two soybean varieties cultivated at two different locations. Our findings may open new insights into soybean agricultural technology.