Expression of Activin Receptor-like Kinase 7 in Adipose Tissues

The tissue distribution of activin receptor-like kinase 7 (Alk7) expression, the signaling ability of Alk7 variants, and Alk7 expression in response to β₃-adrenergic receptor activation were examined. Expression levels of Alk7 varied greatly among tissues but were highest in white adipose tissue and brown adipose tissue. In addition to full-length Alk7 (Alk7-v1), Alk7-v3, an Alk7 variant, was expressed in adipose tissues, brain, and ovary. Nodal transmits signals via Alk7 in cooperation with its coreceptor, Cripto. Evaluation of the ability of Alk7 variants to confer Nodal signaling using luciferase-based reporter assays showed that Alk7-v3 does not transmit Nodal-Cripto-mediated signals. Expression of Alk7 was down-regulated in brown but not in white adipose tissue treated with CL316,243, a β₃-adrenergic receptor agonist. These results suggest involvement of Alk7 in modulation of metabolism in the adipose tissues in response to β₃-adrenergic receptor activation.     

Interaction of Gibberellic Acid and Indole-3-acetic Acid in the Growth of Excised Cuscuta Shoot Tips in Vitro

Gibberellic acid (GA₃) induced a marked elongation of 2.5-centimeter shoot tips of Cuscuta chinensis Lamk. cultured in vitro. In terms of the absolute amount of elongation, this growth may be the largest reported for an isolated plant system. The response to hormone was dependent on an exogenous carbohydrate supply. The hormone-stimulated growth was due to both cell division and cell elongation. The growth response progressively decreased if GA₃ was given at increasingly later times after culturing, but the decreased growth response could be restored by the application of indole-3-acetic acid (IAA) to the apex. Explants deprived of GA₃ gradually lost their ability to transport IAA basipetally, but this ability was also restored by auxin application. The observations are explained on the basis that: (a) the growth of Cuscuta shoot tip in vitro requires, at least, both an auxin and a gibberellin; and (b) in the absence of gibberellin the cultured shoot tip explants lose the ability to produce and/or transport auxin.     

The respiratory function of blood in elderly and old age and the factors that determine it

Indices of pulmonary gas exchange, blood gases, the oxyhemoglobin dissociation curve, and intraerythrocytic metabolic parameters were analyzed in 62 apparently healthy elderly and senile subjects (60–92 years old) and 18 young healthy subjects (19–30 years old). PaO₂ was found to decrease in elderly and senile subjects. Arterial hypoxemia in old age is caused by an increase in the alveoloarterial PO₂ gradient, primarily as a result of the malcoordination of pulmonary ventilation and blood flow. A rightward compensatory shift of the oxyhemoglobin dissociation curve was observed, which was due to facilitated oxygen release in tissues owing to a pH decrease in erythrocytes (the Bohr effect). However, the facilitated oxygen release by oxyhemoglobin cannot compensate for the effect of factors deteriorating oxygen supply delivery to tissues, observed with aging, which is confirmed by the decrease in the partial pressure of oxygen in the venous blood of elderly and senile people, reflecting PO₂ in tissues.     

Competition for phosphorus between two dinoflagellates: A toxic Alexandrium minutum and a non-toxic Heterocapsa triquetra

The understanding of the dominance of one species with respect to others is a pertinent challenge in HAB growth dynamics studies and the nutrient supply mode is one of the factors potentially involved. The competition for phosphorus (P) between a toxic species, Alexandrium minutum, and a non-toxic species, Heterocapsa triquetra, was studied (1) along a gradient of P depletion, (2) testing different P depletion degrees before a single PO₄ supply and (3) experimenting different PO₄ supply frequencies. In conditions of PO₄ depletion, H. triquetra stopped growing after two days both in monospecific and mixed batch cultures whereas A. minutum grew progressively from day 2 until the end of the experiment. This time-lag growth of A. minutum is associated to its ability to store P intracellularly and then mobilize it for cell division when P depletion becomes severe. Heterocapsa triquetra outcompeted A. minutum when it was submitted to less than three days of P depletion before the pulse. In contrast, A. minutum outcompeted H. triquetra after more than three days of depletion. This transition was related to the capacity for A. minutum to increase its cell PO₄ uptake rate in a higher proportion to face potential PO₄ supply. As a result of this physiological acclimatation to P starvation, A. minutum consumed the whole PO₄ pulse supplied after 3 to 10 days of P depletion. This resulted in a reduction of H. triquetra growth. These two acclimatations were confirmed in a P limited semi-continuous culture experiment testing several PO₄ supply frequencies (1, 2, 4, 6 day intervals). These experiments revealed that A. minutum is a “storage specialist” species for P, which uptakes PO₄ pulses for luxury consumption, survives depletion periods and, then, utilizes P for cell growth. In contrast, H. triquetra is more a “velocity adapted” species, which utilizes PO₄ just after supply to increase their cell division rate.     

Proton release of two genotypes of bean (Phaseolus vulgaris L.) as affected by N nutrition and P deficiency

The study compared the release of protons by two genotypes (BAT477 and DOR364) of bean (Phaseolus vulgaris L.) relying on various sources of N (urea, nitrate and N₂ fixation), at two levels of P supply: 1 μM (or 0 for urea-fed plants) and 25 μM. The plants grown at low P showed reduced growth and P concentration in tissues. The proton release was assessed at two levels: (i) at the whole plant level using pH-stat system in hydroponic culture; (ii) at the level of single roots by the combined use of agarose gel-dye indicator and videodensitometry measurements which provided information on the spatial variation of proton release along root axes. The pH-stat measurements showed that urea resulted in the greatest proton release while nitrate led to net hydroxyl release. Moreover, decreased proton release was observed at night for plants relying on urea and N₂ fixation, while no diurnal pattern occurred for plants relying on nitrate. Phophorus deficiency increased proton release in urea-fed plants and decreased hydroxyl release in nitrate-fed plants. Conversely, N₂-fixing plants showed an opposite behaviour, i.e. lower proton release at low than high P supply. Less effect of P supply on proton/hydroxyl release was found at the level of single root tips (videodensitometry experiment) in N₂-fixing plants. Little genotypic difference in proton release was found although BAT477 showed a greater ability to respond to P deficiency than DOR364 when relying on urea or nitrate. Proton release of N₂-fixing plants was greater in BAT477 than in DOR364, both at the whole plant and single root levels.     

Modifying TIMER to generate a slow-folding DsRed derivative for optimal use in quickly-dividing bacteria

It is now well appreciated that members of pathogenic bacterial populations exhibit heterogeneity in growth rates and metabolic activity, and it is known this can impact the ability to eliminate all members of the bacterial population during antibiotic treatment. It remains unclear which pathways promote slowed bacterial growth within host tissues, primarily because it has been difficult to identify and isolate slow growing bacteria from host tissues for downstream analyses. To overcome this limitation, we have developed a novel variant of TIMER, a slow-folding fluorescent protein, named DsRed₄₂, to identify subsets of slowly dividing bacteria within host tissues. The original TIMER folds too slowly for fluorescence accumulation in quickly replicating bacterial species (Escherichia coli, Yersinia pseudotuberculosis), however DsRed₄₂ accumulates red fluorescence in late stationary phase cultures of E. coli and Y. pseudotuberculosis. We show DsRed₄₂ signal also accumulates during exposure to sources of nitric oxide (NO), suggesting DsRed₄₂ signal detects growth-arrested bacterial cells. In a mouse model of Y. pseudotuberculosis deep tissue infection, DsRed₄₂ signal was detected, and primarily accumulates in bacteria expressing markers of stationary phase growth. There was no significant overlap between DsRed₄₂ signal and NO-exposed subpopulations of bacteria within host tissues, suggesting NO stress was transient, allowing bacteria to recover from this stress and resume replication. This novel DsRed₄₂ variant represents a tool that will enable additional studies of slow-growing subpopulations of bacteria, specifically within bacterial species that quickly divide.     

Sites of metabolism of N-nitrosodiethylamine in mice

Low-temperature whole-body autoradiography and autoradiography with heated sections in C57B1 mice injected with N-[¹⁴C]nitrosodiethylamine showed a homogenously distributed volatile radioactivity in most tissues — indicating an ability of the non-metabolized substance to freely pass the biological membranes and distribute evenly in the intra- and extracellular tissue-water. A high level of non-volatile metabolites was found in several tissues: the nasal and tracheal mucosa, the mucosa of the bronchial tree, the salivary glands, the liver, the mucosa of the oesophagus and the tongue, and the lacrimal glands. Studies in vitro indicated that these tissues had a capacity to degrade N-[¹⁴C]nitrosodiethylamine (¹⁴CO₂-production and incorporation of radioactivity in the acid-insoluble material of the tissues were used as indices of the metabolism), whereas several other tissues, which did not accumulate metabolites at short survival intervals in vivo, were devoid of significant metabolic capacity. The relationship between metabolic ability and carcinogenic response of the tissues for N-nitrosodiethylamine is discussed on basis of the obtained results.     

Gibberellin A(1) Biosynthesis in Pisum sativum L. : II. Biological and Biochemical Consequences of the le Mutation

A comparative study of the metabolism of radiolabeled gibberellin (GA) 1, 19, and 20 in isolated vegetative tissues of isogenic Le and le pea (Pisum sativum) plants incubated in vitro with the appropriate GA substrate is described. The results of this study provide evidence that the enzymes involved in the latter stages of GA biosynthesis are spatially separated within the growing pea plant. Apical buds were not apparently involved in the production of bioactive GA₁ or its immediate precursors. The primary site of synthesis of GA₂₀ from GA₁₉ was immature leaflets and tendrils, and the synthesis of bioactive GA₁ and its inactive catabolite GA₈ occurred predominantly in stem tissue. GA₂₉, the inactive catabolite of GA₂₀, was produced to varying extents in all the tissues examined. Little or no difference was observed in the ability of corresponding Le and le tissues to metabolize radiolabeled GA₁, GA₁₉, or even GA₂₀. During a fixed period of 24 hours, stems of plants carrying the le mutation produced slightly more [³H]GA₁ (and [³H]GA₂₉) than those of Le plants. It has been concluded that the le mutation does not lie within the gene encoding the GA₂₀ 3β-hydroxylase protein.     

Influence of energy and nutrient supply pre and post partum on performance of multiparous Simmental,Brown Swiss and Holstein cows in early lactation

A study was conducted to evaluate the effects of pre partum (PRE) and post partum (POST) dietary energy and nutrient supply (E) and their interactions on feed intake, performance and energy status in dairy cows of three breeds. In this experiment, the effects of three energy and nutrient supply levels (low (L), medium (M), high (H)), both pre-calving and post-calving, were investigated, using a 3×3 factorial arrangement of treatments. In both phases (84 days pre- and 105 days post-calving) E levels applied to a total of 81 multiparous cows of breeds Simmental (SI), Brown Swiss (BS) and Holstein–Friesian (HF; n=27 for each breed), were 75%, 100% and 125% of recommendations of the German Society of Nutrition Physiology (GfE). Dry matter intake (DMI) was restricted, if energy intake exceeded target values. Pre partum DMI and energy intake were different as designed, liveweight and body condition score (BCS) of SI cows were higher, but EB was lower, compared to BS and HF cows. Milk yield and composition were influenced by all three main experimental factors (E_PRE, E_POST, breed). Energy-corrected milk yield was 25.6, 28.6 and 30.1 kg/day for L_PRE, M_PRE and H_PRE as well as 21.5, 30.1 and 32.6 kg/day for L_POST, M_POST and H_POST, respectively. Numerically, only for milk protein content the interactions E_PRE×E_POST and E_PRE×breed reached significance. Impact of energy supply pre-calving was more pronounced when cows had lower energy supply post-calving and vice versa. On the other hand, milk yield response of cows to energy supply above requirements was greater for cows that were fed on a low energy level pre partum. Impact of energy level pre partum was higher for HF cows, showing that their milk production relies to a greater extent on mobilization of body reserves. Increasing energy supply pre partum led to a more negative energy balance post partum, mainly by increasing milk yield and content, whereas feed intake was slightly reduced. Increasing energy supply post partum enhanced milk yield as well as milk protein and lactose content. Calculated energy balance corresponded well with liveweight and BCS change. Response of milk yield to increasing energy supply followed the principle of diminishing returns, since energy was increasingly partitioned to body retention. Increasing energy supply pre partum enhances milk yield and content post partum, but exacerbates negative energy balance and its consequences.     

The MeJA-inducible copper amine oxidase AtAO1 is expressed in xylem tissue and guard cells

Copper amine oxidases oxidize the polyamine putrescine to 4-aminobutanal with the production of the plant signal molecule hydrogen peroxide (H₂O₂) and ammonia. The Arabidopsis (Arabidopsis thaliana) gene At4g14940 (AtAO1, previously referred to as ATAO1) encodes an apoplastic copper amine oxidase expressed in lateral root cap cells and developing xylem, especially in root protoxylem and metaxylem precursors. In our recent study, we demonstrated that AtAO1 expression is strongly induced in the root vascular tissues by the wound-signal hormone methyl jasmonate (MeJA). Furthermore, we also demonstrated that the H₂O₂ derived by the AtAO1-driven oxidation of putrescine, mediates the MeJA–induced early protoxylem differentiation in Arabidopsis roots. H₂O₂ may contribute to protoxylem differentiation by signaling developmental cell death and by acting as co-substrate in peroxidase-mediated cell wall stiffening and lignin polymerization. Here, by the means of AtAO1 promoter::green fluorescent protein-β-glucuronidase (AtAO1::GFP-GUS) fusion analysis, we show that a strong AtAO1 gene expression occurs also in guard cells of leaves and flowers. The high expression levels of AtAO1 in tissues or cell types regulating water supply and water loss may suggest a role of the encoded protein in water balance homeostasis, by modulating coordinated adjustments in anatomical and functional features of xylem tissue and guard cells during acclimation to adverse environmental conditions.     

Dependence of in vivo ethylene production rate on 1-aminocyclopropane-1-carboxylic Acid content and oxygen concentrations

1-Aminocyclopropane-1-carboxylic acid (ACC) is aerobically oxidized in plant tissues to form ethylene by ethylene-forming enzyme (EFE). The effect of substrate (ACC and oxygen) concentrations on ethylene production rate by plant tissues was investigated. The K_m value for O₂ in ethylene production varied greatly depending on the internal ACC content. When ACC levels in the tissue were low (below its K_m value), the concentration of O₂ giving half-maximal ethylene production rate ([S]_0.5) ranged between 5 and 7%, and was similar among different tissues. As the concentration of ACC was increased (greater than its K_m value), [S]_0.5 for O₂ decreased markedly. In contrast, the K_m value for ACC was not much dependent on O₂ concentration, but varied greatly among different plant tissues, ranging from 8 micromolar in apple (Malus sylvestris Mill.) tissue to 120 micromolar in etiolated wheat (Triticum aestivum) leaf. Such a great variation was thought to be due to the different compartmentation of ACC within the cells in different tissues. These kinetic data are consistent with the view that EFE follows an ordered binding mechanism in which EFE binds first to O₂ and then to ACC.     

Effect of Ethylene Treatment on Polar IAA Transport, Net IAA Uptake and Specific Binding of N-1-Naphthylphthalamic Acid in Tissues and Microsomes Isolated from Etiolated Pea Epicotyls

The effect of ethylene treatment on polar indole-3-acetic acid (IAA) transport, net IAA uptake in the presence and absence of N-1-naphthylphthalamic acid (NPA) and [³H]NPA binding characteristics was investigated in tissue segments or microsomes isolated from etiolated pea (Pisum sativum L. cv Alaska) epicotyls. Basipetal IAA transport in 5 millimeter segments isolated from ethylene-treated seedlings was inhibited by ethylene in a dose-dependent manner. Threshold, half-maximal and saturating concentrations of ethylene were 0.01, 0.55, 10.0 microliters per liter, respectively. This inhibition became apparent after 6 to 8 hours of ethylene treatment. Transport velocity in both control and ethylene-treated tissues was estimated to be 5 millimeters per hour. Net IAA uptake was stimulated in ethylene-treated tissues and the relative ability of the phytotropin NPA to enhance net IAA uptake was reduced in treated tissues. Specific binding of [³H]NPA to microsomes prepared from both control and ethylene-treated tissues was saturable and consistent with the existence of a single class of binding sites with an apparent affinity (K_d) toward NPA of 8 to 9 nanomolar. The density of these binding sites (per milligram protein) was lower (36% of control) in ethylene-treated tissues. Direct application of ethylene to microsomal preparations isolated from untreated seedlings had no effect on the level of specific [³H]NPA binding.     

Endogenous indole-3-acetic Acid in the stem of tobacco in relation to flower neoformation as measured by mass spectroscopic assay

The contents of free indole-3-acetic acid (IAA) and alkali-labile, conjugated IAA were measured in relation to a `floral gradient' present in epidermis and subepidermis tissues of flowering plants of Nicotiana tabacum by capillary gas-chromatographic spectrometric analysis by selected ion monitoring (GC-SIM-MS) using 2,4,5,6,7-penta deutero IA (²H₅-IAA) as an internal standard. In floral axes, floral branches and stems with floral branches, free IAA levels (dry weight) were 387, 253, and 417 nanograms, and bound IAA levels were 99, 1089, and 268 nanograms. In vegetative tissue of the first plus second internodes (measured from top), and of the 11th to 13th internodes, free IAA levels were 826 and 500 nanograms, and bound IAA levels were 1421 and 286 nanograms, respectively. Since flower-forming ability of excised cells from the epidermis and subepidermis shows a gradient in an in vitro system, but levels of IAA in these tissues do not, there thus appears to be no correlation between flower-forming ability (in vitro) and endogenous IAA levels (at the time of excision) in tobacco stem tissues.     

Influence of phosphorus and nitrogen on photosynthetic parameters and growth in <Emphasis Type="Italic">Vicia faba</Emphasis> L.

The influence of phosphorus (P) and nitrogen (N) supply on biomass, leaf area, photon saturated photosynthetic rate (P_max), quantum yield efficiency (α), intercellular CO₂ concentration (C_i), and carboxylation efficiency (CE) was investigated in Vicia faba. The influence of P on N accumulation, biomass, and leaf area production was also investigated. An increase in P supply was consistently associated with an increase in N accumulation and N productivity in terms of biomass and leaf area production. Furthermore, P increased the photosynthetic N use efficiency (NUE) in terms of P_max and α. An increase in P supply was also associated with an increase in CE and a decrease in C_i. Under variable daily meteorological conditions specific leaf nitrogen content (N_L), specific leaf phosphorus content (P_L), specific leaf area (δ_L), root mass fraction (R_f), P_max, and α remained constant for a given N and P supply. A monotonic decline in the steady-state value of R_f occurred with increasing N supply. δ_L increased with increasing N supply or with increasing N_L. We tested also the hypothesis that P supply positively affects both N demand and photosynthetic NUE by influencing the upper limit of the asymptotic values for P_max and CE, and the lower limit for C_i in response to increasing N.     

Comparative studies on pigments and photosynthetic characteristics of sexually different vegetative and reproductive tissues of Porphyra katadai var. hemiphylla (Bangiales, Rhodophyta)

Porphyra katadai Miura var. hemiphylla Tseng & T.J. Chang, a native species of China, is monoecious with female and male parts in distinct halves separated by a longitudinal line in the blades, and photosynthetic characteristics and pigment contents were compared among different tissues. Female parts contained significantly more phycobiliprotein and carotenoids than male parts did, accompanied by higher photochemical efficiency of photosystem II than the latter. Vegetative tissues had more pigments and higher ΔF/F _m′ and F _v/F _m than their respective reproductive tissues, and male reproductive tissues even exhibited lower P _max based on oxygen evolution than their vegetative tissues at 5–10 °C. Female vegetative tissues showed the highest ΔF/F _m′ among all tissues, while male reproductive tissues had the lowest P _max at low temperatures and the lowest pigment contents. Photosynthesis rates reached the highest values at 10 °C and the lowest values at 20 °C in most tissues, but male reproductive tissues exhibited the best performances at 20 °C, which rarely happened in its natural habitats and growth season. Thus growth capacity and response to seasonal temperature change varied not only between vegetative and reproductive tissues but also between female and male tissues in P. katadai var. hemiphylla, accompanied by their different color and size on wild plants.     

Distribution of nitrate reductase activity in nodulated lucerne plants

Nitrogen fixing plants of lucerne (Medicago sativa L. cv. Aragón) were grown in a glasshouse for three months in the absence of nitrate, and then supplied with 5 mM KNO₃ for a week. In control (non-nitrate fed) plants, nitrate reductase activity (NRA EC 1.6.6.1) was detected only in nodules. After nitrate supply, root NRA showed a transient increase. Shoot NRA increased with time, paralleling changes in nitrate distribution; stem NRA represented nearly 50% of total NRA in plant tissues. Total nitrogen, expressed on a dry weight basis, tended to decrease in shoots upon nitrate supply. Bacteroid NRA (EC 1.7.99.4) showed a great variation depending on Rhizobium meliloti strains, ranging from 5 to 40% of total plant NRA. However, different Rhizobium strains did not give different results in terms of plant growth parameters, nitrate or organic nitrogen content.     

Biofortification of wheat with zinc through zinc fertilization in seven countries

Background and aims

Phosphorus (P) is a commonly limiting nutrient for plant growth in natural environments. Many legumes capable of N₂-fixation require more P than non-legumes do. Some legume crops can use sparingly soluble forms of P such as iron phosphate much better than other species, but reports on the ability of woody legumes to access iron phosphate are rare.

Methods

Plants of four Acacia species (Acacia stipuligera F. Muell., A. ancistrocarpa Maiden & Blakely, A. stellaticeps Kodela, Tindale & D. Keith and A. robeorum Maslin), native to the Great Sandy Desert in north-western Australia, were grown in a glasshouse in river sand with different levels of iron phosphate, between 0 and 16?μg P g^?1 sand. Plant growth, tissue P concentrations, and pH and carboxylates in the rhizosphere were measured.

Results

Growth of A. stipuligera and A. ancistrocarpa was not responsive to increased P supply; in contrast, A. stellaticeps and A. robeorum produced significantly more root and shoot dry mass at 8 and 16?μg P g^?1 sand than at 0?μg P g^?1 sand; differences in root mass ratio were significant between species but not between P treatments. A. robeorum was the only species colonised by mycorrhizal fungi, and the colonisation percentage decreased with increasing P supply. In all species, P-uptake rates and tissue P concentrations were significantly higher at greater P supply. Rhizosphere pH and the amount of carboxylates in the rhizosphere decreased with increasing P supply.

Conclusions

Net P uptake increased with increasing P supply, showing that the present Acacia species can access P from iron phosphate. However, due to their inherently slow growth rate, enhanced P supply did not increase growth of two of the four studied species. The ability of the Acacia species to access P from iron phosphate is presumably related with carboxylate exudation and rhizosphere acidification.     

Limiting Factors in Photosynthesis: V. Photochemical Energy Supply Colimits Photosynthesis at Low Values of Intercellular CO(2) Concentration

Although there is now some agreement with the view that the supply of photochemical energy may influence photosynthetic rate (P) at high CO₂ pressures, it is less clear whether this limitation extends to P at low CO₂. This was investigated by measuring P per area as a function of the intercellular CO₂ concentration (C_i) at different levels of photochemical energy supply. Changes in the latter were obtained experimentally by varying the level of irradiance to normal (Fe-sufficient) leaves of Beta vulgaris L. cv F58-554H1, and by varying photosynthetic electron transport capacity using leaves from Fe-deficient and Fe-sufficient plants. P and C_i were determined for attached sugar beet leaves using open flow gas exchange. The results suggest that P/area was colimited by the supply of photochemical energy at very low as well as high values of C_i. Using the procedure developed by Perchorowicz et al. (Plant Physiol 1982 69:1165-1168), we investigated the effect of irradiance on ribulose bisphosphate carboxylase (RuBPCase) activation. The ratio of initial extractable activity to total inducible RuBPCase activity increased from 0.25 to 0.90 as leaf irradiance increased from 100 to 1500 microeinsteins photosynthetically active radiation per square meter per second. These data suggest that colimitation by photochemical energy supply at low C_i may be mediated via effects on RuBPCase activation.     

The invasive Sorghum halepense harbors endophytic N2-fixing bacteria and alters soil biogeochemistry

Exotic plants invading new habitats frequently initiate broad changes in ecosystem functioning. Sorghum halepense is an invasive grass capable of growing in nitrogen (N)-poor tallgrass prairie soils that creates near monocultures in once phylogenetically diverse-communities. The biogeochemistry of soils invaded by S. halepense was compared to that of un-invaded native prairie soils. Invaded soils contained two to four times greater concentrations of alkaline metals, micronutrients, and essential plant nutrients than native prairie soils. The notable exception was Ca⁺², which was always significantly lower in invaded soils. The N-content of S. halepense above-ground biomass was 6.4 mg g^?1 (320 mg N plant^?1) and suggested a supplemental N source supporting plant growth. Altered soil biogeochemistry in invaded areas coupled with high above-ground biomass in N-poor soils suggested N₂-fixing activity associated with S. halepense. Nitrogenase activity of plant tissues indicated that N₂-fixation was occurring in, and largely restricted to, S. halepense rhizomes and roots. A culture approach was used to isolate these N₂-fixing bacteria from plant tissues, and 16S rRNA gene sequencing was used to identify these bacterial isolates. Nitrogenase activity of bacterial isolates indicated several were capable of N₂-fixation. In addition to N₂-fixation, other roles involved in promoting plant growth, namely mobilizing phosphorus and iron chelation, are known for closest matching relatives of the bacterial isolates identified in this work. Our results indicate that these plant growth-promoting bacteria may enhance the ability of S. halepense to invade and persist by altering fundamental ecosystem properties via significant changes in soil biogeochemistry.