The participation of the cell wall hydrolytic enzymes in the initial colonization of Azospirillum brasilense on wheat roots

The effect of cellulase and pectinase on bacterial colonization of wheat was studied by three different experiments. In the first experiment, the root colonization of 3 wheat cultivars (Ghods, Roshan and Omid) by two A. brasilense strains (Sp7 and Dol) was compared using pre-treated roots with cellulase and pectinase, and non-treated with these enzymes (control). Although the root colonization varied greatly among strain-plant combinations in controls, the pre-treatment of roots with polysaccharide degrading enzymes significantly increased the bacterial count in roots, regardless of the strain-plant combination. This might be an indication that cell wall may act as an important factor in plant-Azospirillum interaction. In the second experiment, the root cellulase activity of the same wheat cultivars treated with and without the two Azospirillum brasilense, strains (Sp7 and Dol) was compared. The pre-treatment of wheat roots with Azospirillum enhanced the cellulase activity of wheat root extracts. Thus, the cellulase activity might participate in the initial colonization of wheat roots by Azospirillum. The comparison of the cellulase activity of root extracts within inoculated and non-inoculated seedlings showed that the inoculation had enhanced the cellulase activity in root extracts, but this effect was directly dependent on the strain-plant combination. Strain Sp7 stimulated the highest cellulase activity in cv. Roshan, but strain Dol induced the highest enzyme activity in cv. Ghods. In the third experiment, several growth parameters of those 3 wheat cultivars treated with and without those two bacterial strains (Sp7 and Dol) were compared. The highest magnitude of growth responses caused by Sp7 strain was in the cv Roshan, but Dol strain stimulated the highest growth in cv Ghods. Therefore, effective colonization may contribute to more growth responses.     

Yield responses of Nepalese spring wheat (Triticum aestivum L.) cultivars to inoculation with Azospirillum spp. of Nepalese origin

Azosprilla were collected in wheat fields from subtropical and temperate soils of central Nepal at various elevations. Different wheat cultivars responded positively and significantly in grain yield, grain N-yield, and total N-yield in plant shoots to the inoculation with Nepalese isolate Azospirillum 10SW. Nepalese wheat cv. Seto responded significantly better with Azospirillum 10SW than with the Brasilian isolate A. lipoferum Sp 108 st, a strain which was found highly efficient in earlier experiments with German wheat cultivars, especially cv. Turbo. Yield of Turbo was increased by inoculations of both Azospirillum strains too, but it showed no significant differences depending from the inoculum used. The higher efficacy of combining Azospirillum 10SW and Seto, both collected from the same locality, indicates the possibility of improved associations using traditional cultivars and local bacteria. ei]{gnR O D}{fnDixon}     

Development and function ofAzospirillum-inoculated roots

Summary The surface distribution ofAzospirillum on inoculated roots of maize and wheat is generally similar to that of other members of the rhizoplane microflora. During the first three days, colonization takes place mainly on the root elongation zone, on the base of root hairs and, to a lesser extent, on the surface of young root hairs.Azospirillum has been found in cortical tissues, in regions of lateral root emergence, along the inner cortex, inside xylem vessels and between pith cells. Inoculation of several cultivars of wheat, corn, sorghum and setaria with several strains ofAzospirillum caused morphological changes in root starting immediately after germination. Root length and surface area were differentially affected according to bacterial age and inoculum level. During the first three weeks after germination, the number of root hairs, root hair branches and lateral roots was increased by inoculation, but there was no change in root weight. Root biomass increased at later stages. Cross-sections of inoculated corn and wheat root showed an irregular arrangement of cells in the outer layers of the cortex. These effects on plant morphology may be due to the production of plant growth-promoting substances by the colonizing bacteria or by the plant as a reaction to colonization. Pectic enzymes may also be involved. Morphological changes had a physiological effect on inoculated roots. Specific activities of oxidative enzymes, and lipid and suberin content, were lower in extracts of inoculated roots than in uninoculated controls. This suggests that inoculated roots have a larger proportion of younger roots. The rate of NO^– ₃, K⁺ and H₂PO^– ₄ uptake was greater in inoculated seedlinds. In the field, dry matter, N, P and K accumulated at faster rates, and water content was higher inAzospirillum-inoculated corn, sorghum, wheat and setaria. The above improvements in root development and function lead in many cases to higher crop yield.     

Carbohydrate and Proline Contents in Leaves, Roots, and Apices of Salt-Tolerant and Salt-Sensitive Wheat Cultivars1

Intra-specific variations in nonstructural carbohydrates and free proline were determined in leaves, apices, roots, and maturing seeds of two salt-tolerant cultivars (CR and Kharchia-65) and one salt-sensitive cv. Ghods of spring wheat (Triticum aestivum L.) grown in sand culture at various levels of salinity (0, 100, 200, and 300 mM NaCl and CaCl₂ at 5 : 1 molar ratio) under controlled environmental conditions. The levels of leaf, apex, and root ethanol-soluble carbohydrates, fructans, starch, and proline increased in line with elevating level of salinity in all three cultivars under investigation. The contents of proline, soluble and insoluble carbohydrates in the apex increased to levels exceeding those in the leaves and roots. Soluble carbohydrate content of salt-sensitive cv. Ghods was higher in the leaves, apices, and roots and lower in the maturing seeds than in the other cultivars at all levels of salinity except at 300 mM. The results show considerable variation in the amount of soluble, insoluble sugars, and proline among plant tissues and wheat genotypes in response to salinity. Higher soluble carbohydrates and fructan in leaves, roots and maturing seeds of stressed plants indicate that their accumulation may help plant to tolerate salinity. Salt-sensitive cv. Ghods accumulated less soluble sugars in the maturing seeds and higher soluble sugars in the apices, which might be used as an indicator in screening wheat genotypes for salinity tolerance.     

Root Hair Deformation, Bacterial Attachment, and Plant Growth in Wheat-Azospirillum Associations

Seven Azospirillum strains induced more deformation of root hairs of wheat than did strains of Rhizobium leguminosarum, Azotobacter chroococcum, or Escherichia coli. Azospirillum sp. strain Sp245 caused the most deformation. Strain Sp245 (isolated from surface sterile roots of wheat) and strain Sp7 (isolated from the rhizosphere of a forage grass) were compared with regard to their effects on root hair deformation, their attachment to roots, and their effects on the growth of four wheat cultivars. The amount of deformation caused by the two strains in the four cultivars increased in the following order: cv. Tobari, cv. Tonari, cv. BH1146, cv. Lagoa. Strain Sp245 attached to the roots of all cultivars in low numbers, and attachment did not increase with time (up to 48 h). Strain Sp7 attached in higher numbers, and attachment increased with time. Inoculation of the four cultivars of wheat had pronounced effects on root mass measured at maturity. The magnitude of the effects in the four cultivars increased in the following order: Tobari, Tonari, BH1146, Lagoa; these effects were progressively more positive for strain Sp245 and progressively more negative for strain Sp7. Concentrations of N in wheat did not vary substantially between cultivars or strains. Concentrations of K and P did not vary substantially between cultivars but did vary between strains, Sp245 effecting increases and Sp7 effecting decreases.     

Alterations in membrane potential and in proton efflux in plant roots induced byAzospirillum brasilense

Inoculation of soybean seedlings withAzospirillum brasilense Cd significantly reduced the membrane potential in every root part and was being maximal in the root elongation zone. Monitoring the proton efflux pattern of inoculated wheat roots by severalA. brasilense strains and byPseudomonas sp. for prolonged periods (up to 200h) revealed a change from the bimodal pattern of proton efflux of non inoculated roots. This change was not related to root colonization ability but to bacterial capacity to induce changes in root surface area. Continuous perfusion of the plant nutrient solution with a fresh solution (from inoculation time), eliminated the enhancing effect of inoculation on proton efflux. We propose thatA. brasilense inoculation influences membrane activity and subsequently proton efflux in roots, probably through the release of an as yet unidentified bacterial signal.     

Field inoculation of sorghum and rice withAzospirillum spp. andHerbaspirillum seropedicae

Two field experiments were carried out at the UAPNPBS experimental station, Seropédica, with two sorghum and one rice cultivars. The establishment, and inoculation effects, ofAzospirillum spp. andHerbaspirillum strains marked with antibiotic resistance were investigated. One grain sorghum (BR 300) and one sugar sorghum (Br 505) cultivar were used.Azospirillum lipoferum strain S82 (isolated from surface sterilized roots of sorghum) established in both cultivars and comprised 40 to 80% of theAzospirillum spp. population in roots and stems 60 days after plant emergence (DAE).Azospirillum amazonense strain AmS91 (isolated from surface-sterilized roots of sorghum) reached only 50%. At 90 DAE, S82 almost disappeared (less than 30% of establishment) while the establishment of AmS91 remained constant in roots and stems. No establishment ofH. seropedicae strain H25 (isolated from surface-sterilized roots of sorghum) orA. lipoferum strain S65 (isolated from the root surface of sorghum) could be observed on inoculated roots. Inoculation with S82, AmS91 or S65 but not withH. seropedicae H25, increased plant dry weight of both cultivars and total N in grain of the grain sorghum. In rice,A. lipoferum Al 121 andA. brasilense Sp 245 (isolated from surface sterilized rice and wheat roots respectively) established in the roots but there was no increase inAzospirillum spp. numbers due to inoculation. None of the strains affected plant growth or rice grain yield.Azospirillum amazonense, A82 andH. seropedicae Z95, which did not establish in roots, significantly enhanced seed germination.     

Establishment of inoculatedAzospirillum spp. in the rhizosphere and in roots of field grown wheat and sorghum

Summary Four field experiments were carried out with wheat or sorghum in different regions of Brazil. The aim was to study the establishment of inoculatedAzospirillum strains, marked with resistance to various antibiotics, in the rhizosphere and in roots. The levels of the various antibiotics were chosen according to the resistance of the indigenousAzospirillum population.Azospirillum brasilense strains Sp 107 and Sp 245 could be established in all three wheat experiments and predominated within theAzospirillum population in washed, and especially in surface sterilized, roots. Strains Sp 7 and Cd established poorly in wheat roots.Azospirillum lipoferum Sp S82 represented 72% of the root isolates from sorghum inoculated with this strain. This strain and naturalAzospirillum infection became concentrated in the upper parts of the root system. Improved methods for root surface sterilization in which the absence ofAzospirillum on the root surface was established by pre-incubating roots with paraffin-capped ends in NFb medium confirmed the establishment of inoculatedAzospirillum strains within sorghum roots in the field.     

Involvement of IAA in the interaction betweenAzospirillum brasilense andPanicum miliaceum roots

The possible involvement of IAA in the effect thatAzospirillum brasilense has on the elongation and morphology ofPanicum miliaceum roots was examined by comparing in a Petri dish system the effects of inoculation with a wild strain (Cd) with those of an IAA-overproducing mutant (FT-326). Both bacterial strains produced IAA in culture in the absence of tryptophan. At the stationary growth phase, production of IAA by FT-326 wasca. 12 times greater than that of Cd. When inoculation was made with bacterial concentrations higher than, 10⁶ colony forming units ml^–1 (CFU ml^–1), both strains inhibited root elongation to the same extent. At lower concentrations Cd enhanced elongation, by 15–20%, while FT-326 was ineffective. Both strains promoted root-hair development, and root-hairs were produced nearer the root tip the higher the bacterial concentration (e. g. root elongation region was reduced). Effects of FT-326 on root-hair development were greater than those of Cd. Acidified ether extracts of Cd and FT-326 cultures had inhibitory or promoting effects on root elongation depending on the dilution applied. At low dilutions, extracts from FT-326 were more inhibitory for elongation than those from Cd. At higher dilutions root elongation was promoted, but FT-326 extracts had to be more diluted than those from Cd. Dilutions that promoted root elongation contained supra-optimal concentrations of IAA, 1–3 orders of magnitude higher than those required for optimal enhancement by synthetic IAA. It is suggested that the bacteria produce in culture an IAA-antagonist or growth inhibitor that decreases the effectiveness of IAA action. The large variability reported for the effects ofAzospirillum on root elongation could be the result of the opposite effects on root elongation of IAA and other compounds, produced by the bacteria.     

Role of bacterial cyanide production in differential reaction of plant cultivars to deleterious rhizosphere pseudomonads

Lettuce and wheat cultivars, differing in reaction to root inoculation with plant growth-inhibitory bacteria, were tested for sensitivity to (i) gaseous metabolites produced by deleterious, cyanogenic isolates of Pseudomonas fluorescens, and to (ii) pure cyanide. Reactions were read as shoot and/or root elongation after exposure of seedlings to the volatiles in vitro. Lettuce cultivar Salad Bowl was significantly less sensitive than cv. Montana, both to bacterial volatiles and to pure cyanide, and a similar difference between these cultivars was also obtained in greenhouse experiments where bacteria were inoculated directly on the roots. Cultivar differences were, however, not recorded, either in vitro or in the greenhouse, when the bacteria were grown on a medium which did not support cyanide production. In wheat, a difference in sensitivity to bacteria-produced volatiles was recorded between two cultivars (Drabant and Besso) differing in reaction to bacterial inoculation, but in contrast to lettuce cultivars, the wheat cultivars tested did not react differentially to pure cyanide. The results suggest that in lettuce differential sensitivity to cyanide is one factor behind cultivar differences in reaction to the bacteria tested, even though bacterial metabolites other than cyanide may contribute to the plant growth inhibition recorded. In wheat, however, differential cultivar responses to these bacteria could not be shown to be related to cyanide.     

Involvement of the Lipopolysaccharides of Azospirilla in the Interaction with Wheat Seedling Roots

The present study was undertaken to comparatively investigate the attachment capacities of Azospirillum brasilenseSp245 and its lipopolysaccharide-defective Omegon-Km mutants KM018 and KM252, as well as their activities with respect to the alteration of the morphology of wheat seedling root hairs. The adsorption dynamics of the parent Sp245 and mutant KM252 strains of azospirilla on the seedling roots of the soft spring wheat cv. Saratovskaya 29 were similar; however, the attachment capacity of the mutant KM252 was lower than that of the parent strain throughout the incubation period (15 min to 48 h). The mutation led to a considerable decrease in the hydrophobicity of the Azospirillumcell surface. The lipopolysaccharides extracted from the outer membrane of A. brasilenseSp245 and mutant cells with hot phenol and purified by chromatographic methods were found to induce the deformation of the wheat seedling root hairs, the lipopolysaccharide of the parent strain being the most active in this respect. The role of the carbohydrate moiety of lipopolysaccharides in the interaction of Azospirillumcells with plants is discussed.     

Exogenously applied paclobutrazol modulates growth in salt-stressed wheat plants

Effect of paclobutrazol (PBZ) treatment on salinity tolerance of wheat (Triticum aestivum) was investigated on a salt-tolerant (Karchia-65) and salt-sensitive (Ghods) cultivars. Salinity significantly reduced the investigated growth parameters such as plant height, length and area of sixth leaf, root length, fresh and dry weight of shoot, roots and sixth leaf, water content (WC) of plant and seeds weight in the both cultivars. The negative effect of salinity in Ghods cultivar was more than Karchia cultivar. However, PBZ treatment reduced the growth in both cultivars, the differences in plant growth among various levels of NaCl decreased in PBZ-treated plants. Salt stress resulted in high accumulation of Na⁺ in the sixth leaf and roots in both cultivars, particularly in Ghods cultivar. Against Karchia cultivar, salt stress decreased the storage of K⁺, P and N in sixth leaf and roots in Ghods cultivar. In the both cultivars, PBZ treatment enhanced the K⁺, P and N contents in sixth leaf and roots by increasing salinity. Although PBZ treatment decreased the growth of plants, it improved the weight of seeds against stress damage. PBZ treatment reduced the accumulation of harmful Na⁺ ion in plant tissues while increased the K⁺, P and N contents. These observations suggest that PBZ treatment may increase tolerance by diminishing ionic imbalance caused by salt stress.     

The effect of aluminium on phosphate uptake by three isolated ectomycorrhizal fungi

Three wheat cultivars with different tolerances against free aluminium were grown monoxenically in association with Azospirillum brasilense. In situ nitrogen fixation, measured with the acetylene reduction assay, was higher by the aluminium-tolerant cultivars than by the sensitive cultivar. The transfer of fixed nitrogen to the host plant, determined by the ¹⁵N dilution technique, was also significantly higher in the aluminium-resistant wheat plants. The total accumulation of fixed nitrogen in the host plants due to an A. brasilense inoculation varied from approximately 13% to 17% of the total nitrogen in the root and 2.9% to 3.9% of the nitrogen in the shoot.The quantity and quality of exudates released in liquid nutrient solution were analysed separately for two of the wheat cultivars, one aluminium-tolerant and one aluminium-sensitive. After 29 days of growth the aluminium-tolerant plants exudated significantly higher total amounts of carbon than aluminium-sensitive plants. No differences between the two cultivars existed in the carbon exudation rate per gram dry root.Much higher concentrations of low molecular dicarboxylic acids i.e. succinic, malic and oxalic acid, were found in the exudates of aluminium-tolerant plants. Dicarboxylic acids are potential chelating compounds for positively charged metals such as aluminium and they may play an important role in protecting the plant against aluminium incorporation. They are also very suitable substrates for Azospirillum spp. It is therefore suggested that these factors may be causing the higher associative nitrogen fixation rates which was found in the aluminium-tolerant wheat cultivars.     

Sodium exclusion mechanisms at the root surface of two maize cultivars

Sodium exclusion at the root surface of intact plants was investigated in two maize cultivars (Zea mays L. cv. Pioneer 3906 and cv. DeKalb XL75). The strong sodium exclusion by Pioneer 3906 relative to DeKalb XL75 was not caused by larger efflux rates. In contrast, this cultivar showed reduced influx rates resulting in about half the net uptake in comparison with DeKalb XL75. It is concluded that the cultivar difference in sodium exclusion at the root surface is based on a relatively low passive sodium permeability of the epidermal and cortex plasmalemma of Pioneer 3906. For both cultivars, the flux ratio equation indicated an active component of sodium efflux.     

Adsorption and anchoring of Azospirillumstrains to roots of wheat seedlings

Recent microscopic evidence acquired using strain-specific monoclonal antibodies and specific gene probes confirms earlier claims that some strains of Azospirillum lipoferum and A. brasilense, but not others, are capable of infecting the interior of wheat roots. The present study was performed to determine whether this strain specificity in the infection of the interior of wheat roots was apparent in the first 24 h of adsorption (`anchoring') of Azospirillum cells to the root surface. Strains of A. brasilense, originally isolated from surface-sterilised wheat roots (Sp 245, Sp 107) or with a proven ability to infect the interior of wheat roots (Sp 245), showed no greater ability to anchor to the roots than other Azospirillum strains isolated from the wheat rhizosphere (Sp 246) or from the rhizosphere or rhizosphere soil of other gramineae (Sp 7, Cd, S 82). The SEM images showed that at the root tip the Azospirillum cells were principally located in cracks between epidermal cells. In the root hair zone the bacteria were more numerous but again principally located in the depressions between epidermal cells. In all zones of the roots mucilage was present, and near the tip this appeared to have been partially digested, forming `halos' around the bacteria and revealing fibril-like strands attached to the bacteria. Subsequent studies were conducted using a technique originally developed for investigating competition of rhizobia for adsorption sites on legume roots. In the adaptation of this technique it was found that the presence of any significant concentration of Ca⁺⁺ in the incubation medium reduced bacterial adsorption, as did concentrations of (PO₄)^3- above 50 mM. The influence of the pH of the incubation medium on the adsorption of ten different strains of Azospirillum showed, that with one exception, strains isolated from the roots or rhizosphere of wheat showed optimum adsorption at pH 6.0, and all other strains pH 7.0. Apart from this effect of pH no differences in adsorption were detected between strains with a proven capacity to infect wheat roots and those unable to do so. However, strains varied in their capability to compete for adsorption sites, there being a tendency for strains with a proven capacity to invade the internal tissues of wheat roots to be more competitive for adsorption sites.     

Effect of seed inoculation,mycorrhizal infection and organic amendment on wheat growth

Summary The effect of seed inoculation withAzotobacter spp. orAzospirillum spp., and garbage amendment (0.5%), on the growth of wheat was studied in a field experiment under sub-tropical conditions. Two levels of N fertilizer were applied, the usual field rate (150 kg N ha^–1) and half this amount. Tillering of plants, dry matter contents and nitrogenase activity were determined 30, 60 and 90 days after sowing. At the end of the experimental period, spore numbers and percentage of mycorrhizal infection were observed in the rhizosphere and root systems of plants. Straw and grain yields were also determined. The results of this study showed that seed inoculation and/or organic amendment stimulated plant growth, nitrogenase activity and mycorrhizal infection. This was more noticeable withAzotobacter than withAzospirillum. Inoculation withAzotobacter together with 1/2 N dose and organic amendment was the most effective application (19.75 and 10.70 t ha^–1 were recorded for straw and grain yield, respectively).     

Natural occurrence of Azospirillum brasilense in strawberry plants

Azospirillum species are free-living nitrogen-fixing bacteria commonly found in soil and in association with roots of different plant species. For their capacity to stimulate growth they are known as plant growth-promoting bacteria (PGPB). In this work, we demonstrate the natural occurrence and colonization of different parts of strawberry plants by Azospirillum brasilense in the cropping area of Tucumán, Argentina. Although bacteria isolations were carried out from two strawberry cultivars, e.g., Camarosa and Pájaro, attempts were successful only with the cultivar Camarosa. Whereas different strains of Azospirillum were isolated from the root surface and inner tissues of roots and stolons of the cultivar Camarosa, we have not obtained Azospirillum isolates from the cultivar Pájaro. After microbiological and molecular characterization (ARDRA) we determined that the isolates belonged to the species A. brasilense. All isolates showed to have the capacity to fix nitrogen, to produce siderophores and indoles. Local isolates exhibited different yields of indoles production when growing in N-free NFb semisolid media supplemented or not with tryptophan (0.1 mg ml⁻¹). This is the first report on the natural occurrence of A. brasilense in strawberry plants, especially colonizing inner tissues of stolons, as well as roots. The local isolates showed three important characteristics within the PGPB group: N₂-fixation, siderophores, and indoles production.     

Effects of Salinity and Relative Humidity on Two Melon Cultivars Differing in Salt Tolerance

The effects of increasing relative humidity on the growth and salt tolerance of two melon (Cucumis melo L.) cultivars, Revigal C-8 (salt sensitive) and Galia (salt tolerant) was investigated. One month after germination, the plants were exposed for 15 d to 0 (control) and 80 mM NaCl, under relative humidity (RH), 30 and 70 %. The growth of the whole plant, leaf, stem and root of cv. Revigal C-8 was increased with increasing RH. On the other hand, cv. Galia showed an increase in root growth with increasing RH only under the NaCl treatment. Under salinity, most of the Na⁺ was withheld in the stems. An increase in RH in the NaCl treatment significantly decreased Na⁺ and Cl^– concentrations in leaves of cv. Revigal C-8, while it had no effect on their concentrations in cv. Galia. In both cultivars, increasing RH under NaCl condition significantly decreased water contents in leaves and stems, and increased osmotic potential in roots. The amount of the root exudate of cv. Galia was significantly decreased with increasing RH, while it was not affected in cv. Revigal C-8. Under the NaCl treatment, cv. Galia had significantly higher leaf osmotic potential than cv. Revigal C-8 at both relative humidities and higher amount of root exudate at 30 % RH.     

Nitric Oxide is Involved in the <Emphasis Type="Italic">Azospirillum brasilense</Emphasis>-induced Lateral Root Formation in Tomato

Azospirillum spp. is a well known plant-growth-promoting rhizobacterium. Azospirillum-inoculated plants have shown to display enhanced lateral root and root hair development. These promoting effects have been attributed mainly to the production of hormone-like substances. Nitric oxide (NO) has recently been described to act as a signal molecule in the hormonal cascade leading to root formation. However, data on the possible role of NO in free-living diazotrophs associated to plant roots, is unavailable. In this work, NO production by Azospirillum brasilense Sp245 was detected by electron paramagnetic resonance (6.4 nmol. g^–1 of bacteria) and confirmed by the NO-specific fluorescent probe 4,5-diaminofluorescein diacetate (DAF-2 DA). The observed green fluorescence was significantly diminished by the addition of the specific NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). Azospirillum-inoculated and noninoculated tomato (Lycopersicon esculentum L.) roots were incubated with DAF-2 DA and examined by epifluorescence microscopy. Azospirillum-inoculated roots displayed higher fluorescence intensity which was located mainly at the vascular tissues and subepidermal cells of roots. The Azospirillum-mediated induction of lateral root formation (LRF) appears to be NO-dependent since it was completely blocked by treatment with cPTIO, whereas the addition of the NO donor sodium nitroprusside partially reverted the inhibitory effect of cPTIO. Overall, the results strongly support the participation of NO in the Azospirillum-promoted LRF in tomato seedlings.     

Selection of Tn5::lacZ mutants isogenic to wild type Azospirillum brasilense strains capable of growing at sub-optimal temperature

Azospirillum brasilense strains, CDJA and A40, capable of growing at sub-optimal temperature were tagged with stable chromogenic marker Tn5-lacZ. Mutants were screened for plant growth promoting activities at 20, 22, 25, 30 and 37 °C. Mutants MC48 and MA3 were found to fix nitrogen upto 85% and produced indole acetic acid (IAA) and siderophore in isogenic manner to their respective wild type strains, CDJA and A40, at sub-optimal temperatures. Co-inoculation of mutants with their respective parent (1:1 ratio) to the wheat revealed that colonization potential of the mutants was affected greatly. Tn5-lacZ tagged mutants MC48 and MA3 were found isogenic to their respective wild type Azospirillum strain, with regards to plant growth promoting activities and root colonization ability. This revised version was published online in July 2006 with corrections to the Cover Date.