Enhanced Mineral Uptake by Zea mays and Sorghum bicolor Roots Inoculated with Azospirillum brasilense

Inoculation of corn (Zea mays) seeds with Azospirillum brasilense strain Cd or Sp 7 significantly enhanced (30 to 50% over controls) the uptake of NO₃⁻, K⁺, and H₂PO₄⁻ into 3- to 4-day- and 2-week-old root segments. No gross changes in root morphology were observed; altered cell arrangement in the outer four or five layers of the cortex was seen in photomicrographs of cross sections of inoculated corn roots. The surface activity involved in ion uptake probably increased, as shown by the darker staining by methylene blue of the affected area. Shoot dry weight increased 20 to 30% in inoculated plants after 3 weeks, presumably by enhancement of mineral uptake. Corn and sorghum plants grown to maturity on limiting nutrients in the greenhouse showed improved growth from inoculation approaching that of plants grown on normal nutrient concentrations. Enhanced ion uptake may be a significant factor in the crop yield enhancement reported for Azospirillum inoculation.     

Les échanges de nourriture liquide entre Abeilles aux températures élevées

Conclusion Nous avons démontré des échanges assez importants du liquide entre les Abeilles aux températures élevées. Cette répartition est exprimée pour la première fois quantitativement. Nous supposons que c'est un phénomène d'une réaction thermorégulatrice sur le plan social. Nous sommes en train de vérifier si cette réaction crée un microclimat différent autour des Abeilles dans ces conditions expérimentales.     

Aerotaxis and chemotaxis ofAzospirillum brasilense: A note

Azospirillum brasilense was attracted to capillaries containing either phosphate buffer, distilled water, or saline. The number of bacteria in these capillaries was 3–4×10⁴, after 1 h of incubation. In the presence of phosphate buffer + attractants, the number of cells accumulated in the capillary increased only to 5×10⁴–1.1×10⁵ cells. It was not possible, therefore, to measure chemotaxis inA. brasilense as distinct from aerotaxis by the capillary method. Chemotaxis was observed in semi-solid agar plates and was determined by a growth band oriented towards the attractant. Positive chemotactic response was obtained with peptone, tryptone, yeast extract, amino acids, organic acids, arabinose and galactose.     

Fruit cuticle lipid composition and water loss in a diverse collection of pepper (Capsicum)

Pepper (Capsicum spp.) fruits are covered by a relatively thick coating of cuticle that limits fruit water loss, a trait previously associated with maintenance of postharvest fruit quality during commercial marketing. To shed light on the chemical‐compositional diversity of cuticles in pepper, the fruit cuticles from 50 diverse pepper genotypes from a world collection were screened for both wax and cutin monomer amount and composition. These same genotypes were also screened for fruit water loss rate and this was tested for associations with cuticle composition. Our results revealed an unexpectedly large amount of variation for the fruit cuticle lipids, with a more than 14‐fold range for total wax amounts and a more than 16‐fold range for cutin monomer amounts between the most extreme accessions. Within the major wax constituents fatty acids varied from 1 to 46%, primary alcohols from 2 to 19%, n‐alkanes from 13 to 74% and triterpenoids and sterols from 10 to 77%. Within the cutin monomers, total hexadecanoic acids ranged from 54 to 87%, total octadecanoic acids ranged from 10 to 38% and coumaric acids ranged from 0.2 to 8% of the total. We also observed considerable differences in water loss among the accessions, and unique correlations between water loss and cuticle constituents. The resources described here will be valuable for future studies of the physiological function of fruit cuticle, for the identification of genes and QTLs associated with fruit cuticle synthesis in pepper fruit, and as a starting point for breeding improved fruit quality in pepper.     

New Metabolites of Streptomyces alboniger

A mutant unable to grow under acidic conditions was isolated from the acidophilic heterotrophic bacterium Acidiphilium facilis 24R. The growth of the mutant could be fully restored by the addition of spermidine or lysine at the concentration of 100 μm. The HPLC analysis of polyamine composition showed that spermidine and putrescine were major polyamine components in the parental strain. In the mutant strain, putrescine was replaced by cadaverine. It was found that some polyamines in the cells were conjugated with the other cell components. The growth of the bacterium in the medium below pH 4.5 was inhibited in the presence of α-methylornithine or methylglyoxal-bis(guanylhydrazone), which are inhibitors of rate-limiting enzymes involved in the biosynthesis of polyamines. The growth of the bacterium that had been inhibited in the presence of inhibitors could be fully restored by the addition of putrescine or spermidine. On the basis of these results, it was concluded that polyamines have a significant role in the growth of Acidiphilium facilis 24R under acidic conditions.     

Interplay between hnRNP A1 and a cis-acting element in the 3' UTR of CYP2A5 mRNA is central for high expression of the gene

Our previous evidence suggests that heterogeneous nuclear ribonucleoprotein (hnRNP) A1 plays a part in the regulation of the Cyp2a5 gene by interacting with the 3' untranslated region (UTR) of the CYP2A5 mRNA. However, the exact role of this interaction is not clear. The aim of the present work was to gain further insight into the regulation process of Cyp2a5. For this purpose the 3' UTR of CYP2A5 was fused to the coding region of luciferase mRNA. Luciferase recombinants containing either the full length 3' UTR, or the 3' UTR lacking a previously described 71 nucleotide (nt) region (the hnRNP A1 primary binding site), were transiently expressed in cells expressing or lacking hnRNP A1. The expression of the luciferase recombinants was examined both at mRNA and enzyme activity levels. The results disclosed that the presence of hnRNP A1 was required for the high expression of the recombinant carrying the full length 3' UTR of CYP2A5. Deletion of the hnRNP A1 primary binding site dramatically modified the expression pattern: the mRNA levels and luciferase activities of the deletion mutant were independent from hnRNP A1. These results conclusively demonstrate that the 71 nt region in the 3' UTR of CYP2A5 mRNA can confer hnRNP A1-dependent regulation to a gene. In addition, comparison of RNA levels and luciferase activities suggested that regions flanking the hnRNP A1 binding site could regulate translation of the CYP2A5 mRNA. These results are consistent with a model in which the binding of hnRNP A1 to the 71 nt putative hairpin-loop region in the CYP2A5 mRNA 3' UTR upregulates mRNA levels possibly by protecting the mRNA from degradation.     

Laccase activity in melanin-producing strains of Sinorhizobium meliloti

Laccase-like activity was detected in melanin-producing strains of Sinorhizobium meliloti mainly in cells at the stationary growth phase when copper was added to the medium. The laccase showed both syringaldazine and ABTS (2,2'-azino-bis-ethylbenzthiazoline-6-sulfonic acid) oxidase activities and was activated by the addition of 1.7 mM sodium dodecyl sulfate. Activity was totally inhibited by the addition of 1.0 mM EDTA, suggesting that the enzyme is a metal-dependent one. The enzyme was found to be cytosolic having an optimum pH of 5.0, an estimated molecular mass of 95 kDa and a K(m) of 4 microM for syringaldazine. Both laccase and tyrosinase activities were detected in melanin-producing S. meliloti strains. Plant growth-promoting (PGP) effect in rice by a laccase-producing S. meliloti strain when co-inoculated with Azospirillum brasilense Cd was observed. PGP effect by co-inoculation significantly increased plant yield compared to A. brasilense by itself. To the best of our knowledge this is the first report on laccase production in rhizobia and cooperation between Azospirillum and Sinorhizobium in rice.     

A thioredoxin of Sinorhizobium meliloti CE52G is required for melanin production and symbiotic nitrogen fixation

A miniTn5-induced mutant of a melanin-producing strain of Sinorhizobium meliloti (CE52G) that does not produce melanin was mapped to a gene identified as a probable thioredoxin gene. It was proved that the thiol-reducing activity of the mutant was affected. Addition to the growth medium of substrates that induce the production of melanin (L-tyrosine, guaiacol, orcinol) increased the thioredoxin-like (trxL) mRNA level in the wild-type strain. The mutant strain was affected in the response to paraquat-induced oxidative stress, symbiotic nitrogen fixation, and both laccase and tyrosinase activities. The importance of thioredoxin in melanin production in bacteria, through the regulation of laccase or tyrosinase activities, or both, by the redox state of structural or catalytic SH groups, is discussed.     

Ischemic preconditioning decreases the reperfusion-related formation of hydroxyl radicals in a rabbit model of regional myocardial ischemia and reperfusion: the role of K(ATP) channels

The objective of this study was to assess the effects of ischemic preconditioning (IP) on hydroxyl free radical production in an in vivo rabbit model of regional ischemia and reperfusion. Another goal was to determine whether K_ATP channels are involved in these effects.

The hearts of anesthetized and mechanically ventilated New Zealand White rabbits were exposed through a left thoracotomy. After IV salicylate (100 mg/kg) administration, all animals underwent a 30-min stabilization period followed by 40 min of regional ischemia and 2 h of reperfusion. In the IP group, IP was elicited by 5 min of ischemia followed by 10 min of reperfusion (prior to the 40-min ischemia period). Glibenclamide, a K_ATP channel blocker, was administered prior to the preconditioning stimulus. Infarct size was measured by 2,3,5-triphenyl tetrazolium chloride (TTC) staining. We quantified the hydroxyl-mediated conversion of salicylate to its 2,3 and 2,5-dihydroxybenzoate derivatives during reperfusion by high performance liquid chromatography coupled with electro-chemical detection.

IP was evidenced by reduced infarct size compared to control animals: 22% vs. 58%, respectively. Glibenclamide inhibited this cardioprotective effect and infarct size was 53%. IP limited the increase in 2,3 and 2,5-dihydroxybenzoic acid to 24.3 and 23.8% above baseline, respectively. Glibenclamide abrogated this effect and the increase in 2,3 and 2,5-dihydroxybenzoic acid was 94.3 and 85% above baseline levels, respectively, similar to the increase in the control group. We demonstrated that IP decreased the formation of hydroxyl radicals during reperfusion. The fact that glibenclamide inhibited this effect, indicates that K_ATP channels play a key role in this cardioprotective effect of IP.     

Key physiological properties contributing to rhizosphere adaptation and plant growth promotion abilities of Azospirillum brasilense

Azospirillum brasilense is a plant growth promoting rhizobacterium (PGPR) that is being increasingly used in agriculture in a commercial scale. Recent research has elucidated key properties of A.?brasilense that contribute to its ability to adapt to the rhizosphere habitat and to promote plant growth. They include synthesis of the auxin indole-3-acetic acid, nitric oxide, carotenoids, and a range of cell surface components as well as the ability to undergo phenotypic variation. Storage and utilization of polybetahydroxyalkanoate polymers are important for the shelf life of the bacteria in production of inoculants, products containing bacterial cells in a suitable carrier for agricultural use. Azospirillum brasilense is able to fix nitrogen, but despite some controversy, as judging from most systems evaluated so far, contribution of fixed nitrogen by this bacterium does not seem to play a major role in plant growth promotion. In this review, we focus on recent advances in the understanding of physiological properties of A.?brasilense that are important for rhizosphere performance and successful interactions with plant roots.