Confocal pH Topography in Plant Cells — Acidic Layers in the Peripheral Cytoplasm and the Apoplast

The distribution of intracellular pH was studied in cultured cells of Gossypium hirsutum by con-focal pH topography using the fluorescent probe car-boxy SNARF1 and a ratio imaging procedure. The resulting pH maps can visualize pH differences with an accuracy of 0.1 unit in the investigated range between 7.5 and 5.6. They reveal the following characteristic features of the Gossypium cells: – the pH of the cytoplasmic core regions ranges from near 7.4 in younger to near 6.0 in older cells; – vacuoles show the expected acidity with pH < 5.6; – the cell wall/apoplastic region is acidic with a pH near 5.6 or below, especially in young, growing cells; – interestingly, acidic areas appear also at the periphery of the cytoplasm, i.e. beneath the plasma membrane. They remain stable in the presence of 5/μmol/I of the protonophore CCCP. Acidic layers of peripheral cytoplasm were also detected in protoplasts of Penicillium cyclopium, i.e. eukaryotic cells of simpler structure, which served as a reference object. This ronfirms earlier findings obtained with classical fluorescence microscopy and another fluoroprobe (fluorescein diacetate). Though additional experimental support is needed, low pH regions at the cytoplasm/plasma membrane interface should be considered a real contribution to the pH control of plant and fungal cells, facilitating e.g. the maintenance of cytosolic pH in acidic environments.     

Carbazole–azine based fluorescence ‘off–on’ sensor for selective detection of Cu2+ and its live cell imaging

A new carbazole–azine based fluorescent sensor was synthesized and characterized. The selectivity of the sensor for Cu²⁺ over other counter ions in a dimethyl sulfoxide/H₂O mixture was shown through enhancement in fluorescence – an off to on transformation. The specificity of the probe towards Cu²⁺ was evident in ultraviolet/visible, fluorescence, Fourier transform infrared and mass studies. Application of the probe in the cell imaging and cytotoxicity of living cells is illustrated.     

Inhibition of α-, β-, γ-, and δ-carbonic anhydrases from bacteria and diatoms with N′-aryl-N-hydroxy-ureas

The inhibition of α-, β-, γ-, and δ-class carbonic anhydrases (CAs, EC 4.2.1.1) from bacteria (Vibrio cholerae and Porphyromonas gingivalis) and diatoms (Thalassiosira weissflogii) with a panel of N’-aryl-N-hydroxy-ureas is reported. The α-/β-CAs from V. cholerae (VchCAα and VchCAβ) were effectively inhibited by some of these derivatives, with K_Is in the range of 97.5?nM – 7.26?µM and 52.5?nM – 1.81?µM, respectively, whereas the γ-class enzyme VchCAγ was less sensitive to inhibition (K_Is of 4.75 – 8.87?µM). The β-CA from the pathogenic bacterium Porphyromonas gingivalis (PgiCAβ) was not inhibited by these compounds (K_Is?>?10?µM) whereas the corresponding γ-class enzyme (PgiCAγ) was effectively inhibited (K_Is of 59.8?nM – 6.42?µM). The δ-CA from the diatom Thalassiosira weissflogii (TweCAδ) showed effective inhibition with these derivatives (K_Is of 33.3?nM – 8.74?µM). As most of these N-hydroxyureas are also ineffective as inhibitors of the human (h) widespread isoforms hCA I and II (K_Is?>?10?µM), this class of derivatives may lead to the development of CA inhibitors selective for bacterial/diatom enzymes over their human counterparts and thus to anti-infectives or agents with environmental applications.     

A Phenazine based colorimetric and fluorescent chemosensor for sequential detection of Ag+ and I− in aqueous media

A new colorimetric and fluorescent probe MNTPZ based on 1H‐imidazo[4,5‐b]phenazine derivative has been designed and synthesized for successive detection of Ag⁺ and I^?. The probe MNTPZ shows selective colorimetric response by a change in color from yellow to orange and “turn‐off” fluorometric response upon binding with Ag⁺ in DMSO: Water (pH = 7, 1:1, v/v) over other cations. The binding mode of probe MNTPZ to Ag⁺ was studied by Job's plot, ¹H NMR studies, FT‐IR spectroscopy and DFT calculations. Moreover, the situ generated probe MNTPZ + Ag⁺ complex acted as an efficient fluorometric “turn‐on” probe for I^? via Ag⁺ displacement approach. The detection limit of probe MNTPZ for Ag⁺ and the resultant complex probe MNTPZ + Ag⁺ for I^? were determined to be 1.36 μmol/L and 1.03 μmol/L respectively. Notably, the developed probe was successfully used for quantitative determination of I^? in real samples with satisfactory results.     

Fluorescent sensors based on quinoline‐containing styrylcyanine: determination of ferric ions,hydrogen peroxide,and glucose,pH‐sensitive properties and bioimaging

A novel styrylcyanine‐based fluorescent probe 1 was designed and synthesized via facile methods. Ferric ions quenched the fluorescence of probe 1, whereas the addition of ferrous ions led to only small changes in the fluorescence signal. When hydrogen peroxide was introduced into the solution containing probe 1 and Fe²⁺, Fe²⁺ was oxidized to Fe³⁺, resulting in the quenching of the fluorescence. The probe 1/Fe²⁺ solution fluorescence could also be quenched by H₂O₂ released from glucose oxidation by glucose oxidase (GOD), which means that probe 1/Fe²⁺ platform could be used to detect glucose. Probe 1 is fluorescent in basic and neutral media but almost non‐fluorescent in strong acidic environments. Such behaviour enables it to work as a fluorescent pH sensor in both the solution and solid states and as a chemosensor for detecting volatile organic compounds with high acidity and basicity. Subsequently, the fluorescence microscopic images of probe 1 in live cells and in zebrafish were achieved successfully, suggesting that the probe has good cell membrane permeability and a potential application for imaging in living cells and living organisms. Copyright © 2014 John Wiley & Sons, Ltd.     

Dependence of sodium-calcium exchange current through the membrane of salivary gland cells ofChironomus on pH of the extracellular solution

The dependence of sodium-calcium exchange current (I _Na(Ca)) through the membrane of isolated secretory cells ofChironomus larva on pH of the extracellular solution was studied with the voltage-clamp technique with intracellular perfusion.I _Na(Ca) evoked by hyperpolarization of the membrane from –20 to –60 mV was recorded within physiological values of Na⁺ and Ca²⁺ gradients. It was established that acidification of extracellular solution from pH 7.2 to 4.0 gradually decreased the amplitude ofI _Na(Ca) with pK' — 3.72. In all cases at pH 3.0 an outward current of considerable amplitude emerged in response to membrane hyperpolarization. The reversal of the current occurred at pH around 3.25. A decrease inI _Na(Ca) was due to protonation of acid ionogenic groups (quite possibly, of the residues of aspartic or glutamic amino acids), which had been involved in binding of cations. Alkalization of extracellular solution from pH 7.2 to 10.0 produced a gradual increase in theI _Na(Ca) amplitude; pK' was in the pH range between 9 and 10. The increase inI _Na(Ca) in alkaline medium was probably due to the appearance of negatively charged cations at binding sites, which could be carried by deprotonated thiosulfate groups of cysteine residues. This was indicated by the possibility of initial decrease inI _Na(Ca) under the action of Hg²⁺ ions.Neirofiziologiya/Neurophysiology, Vol. 28, No. 4/5, pp. 193–196, July–October, 1996.     

A proton-activated, outwardly rectifying chloride channel in human umbilical vein endothelial cells

Extracellular acidic pH-activated chloride channel I_{Cl, acid}, has been characterized in HEK 293 cells and mammalian cardiac myocytes. This study was designed to characterize I_Cl,acid in human umbilical vein endothelial cells(HUVECs). The activation and deactivation of the current rapidly and repeatedly follows the change of the extracellular solution at pH 4.3, with the threshold pH 5.3. In addition, at very positive potentials, the current displays a time-dependent facilitation. pH-response relationship for I_Cl,acid revealed that EC₅₀ is pH 4.764 with a threshold pH value of pH 5.3 and nH of 14.545. The current can be blocked by the Cl⁻ channel inhibitor DIDS (100 μM). In summary, for the first time we report the presence of proton-activated, outwardly rectifying chloride channel in HUVECs. Because an acidic environment can develop in local myocardium under pathological conditions such as myocardial ischemia, I_Cl,acid would play a role in regulation of EC function under these pathological conditions.     

Temperature- and pH-Induced Structural Changes in the Membrane of the Hyperthermophilic Archaeon Aeropyrum pernix K1

The influence of pH and temperature on the structural organization, fluidity and permeability of the hyperthermophilic archaeon membrane was investigated in situ by a combination of electron paramagnetic resonance (EPR) and fluorescence emission spectroscopy. For EPR measurements, Aeropyrum pernix cells, after growing at different pHs, were spin-labeled with the doxyl derivative of palmitic acid methylester (MeFASL[10,3]). From the EPR spectra maximal hyperfine splitting (2A _max) and empirical correlation time (τ_emp), which are related to mean membrane fluidity, were determined. The mean membrane fluidity increases with temperature and depends on the pH of the growth medium. Computer simulation of the EPR spectra shows that membrane of A. pernix is heterogeneous and consists of the regions characterized with three different types of motional characteristics, which define three types of membrane domains. Order parameter and proportion of the spin probes in the three types of domains define mean membrane fluidity. The fluidity changes of the membrane with pH and temperature correlate well with the ratio between the fluorescence emission intensity of the first and third bands in the vibronic spectra of pyrene, I₁/I₃. At pH 7.0 a decrease of I₁/I₃ from 2.0 to 1.2, due to the penetration of pyrene into the nonpolar membrane region, is achieved at temperatures above 65°C, the lower temperature limit of A. pernix growth.     

Photosynthetic characteristics of charophytes from tropical lotic ecosystems

Responses of photosynthetic rates, determined by oxygen evolution using the light and dark bottles technique, to different temperatures, irradiances, pH, and diurnal rhythm were analyzed under laboratory conditions in four charophyte species (Chara braunii Gmelin, C. guairensis R. Bicudo, Nitella subglomerata A. Braun and Nitella sp.) from lotic habitats in southeastern Brazil. Parameters derived from the photosynthesis versus irradiance curves indicated affinity to low irradiances for all algae tested. Some degree of photoinhibition, [β= ‐(0.30–0.13) mg O2 g^?1 dry weight Ir¹ (μmol photons m^?2 s^?1)^?1], low light compensation points (I_c= 4–20 μmol photons m^?2 s^?1) were found for all species analyzed, as well as low values of light saturation parameter (I_k) and saturation (I_s) 29–130 and 92–169 μmol photons m^?2 s^?1, respectively. Photoacclimation was observed in two populations of N. subglomerata collected from sites with different irradiances, consisting of variations in photosynthetic parameters (higher values of a, and lower of I_k and maximum photosynthetic rate, P_max, in the population under lower irradiance). The highest photosynthetic rates for Chara species were observed at 10–15°C, while for Nitella the highest photosynthetic rate was observed at 20–25°C, despite the lack of significant differences among most levels tested. Rates of dark respiration significantly increase with temperature, with the highest values at 25°C. The results from pH experiments showed highest photosynthetic rates under pH 4.0 for all algae, suggesting higher affinity for inorganic carbon in the form of carbon dioxide, except in one population of N. subglomerata, with similar rates under the three levels, suggesting indistinct use of bicarbonate and carbon dioxide. Diurnal changes in photosynthetic rates revealed a general pattern for most algae tested, which was characterized by two peaks: the first (higher) during the morning (07.00–11.00) and the second (lower) in the afternoon (14.00–17.00). This suggests an endogenous rhythm determining the daily variations in photosynthetic rates.     

A new fluorescent pH probe for imaging lysosomes in living cells

A new rhodamine B-based pH fluorescent probe has been synthesized and characterized. The probe responds to acidic pH with short response time, high selectivity and sensitivity, and exhibits a more than 20-fold increase in fluorescence intensity within the pH range of 7.5–4.1 with the pK_a value of 5.72, which is valuable to study acidic organelles in living cells. Also, it has been successfully applied to HeLa cells, for its low cytotoxicity, brilliant photostability, good membrane permeability and no ‘alkalizing effect’ on lysosomes. The results demonstrate that this probe is a lysosome-specific probe, which can selectively stain lysosomes and monitor lysosomal pH changes in living cells.     

Stress Tolerance and Genetic Variability of Phosphate-solubilizing Fluorescent Pseudomonas from the Cold Deserts of the Trans-Himalayas

Nineteen efficient phosphate-solubilizing fluorescent Pseudomonas from the cold deserts of the trans-Himalayas were screened for stress tolerance against temperature, alkalinity, salinity, calcium salts, and desiccation. Phylogenetic analysis based on 16S rRNA gene sequencing placed these bacteria under three groups with fourteen strains in Group I including Pseudomonas trivialis and P. poae, two strains in Group II together with Pseudomonas kilonensis and P. corrugata, and three strains in Group III along with Pseudomonas jessenii and P. moraviensis. Genetic diversity assessed by ERIC and BOX-PCR revealed variability among strains belonging to the same phylogenetic groups. Cluster analysis based on the growth characteristics under regimes of different stress levels placed the strains into three distinct clusters displaying no correlation to their phylogenetic groups. Stress-tolerant strains differed in the level of decline in phosphate solubilization under increasing intensity of various stress parameters. The highest decrease occurred with 5% CaCO_3, followed by 2.5% CaCO₃, pH 11, 5% NaCl, temperature of 37°C, 40% PEG, 5% CaSO₄, 2.5% NaCl, 2.5% CaSO₄, pH 9 and temperature of 15°C. Two strains belonging to Phylogenetic Group I exhibited higher phosphate solubilization at lower temperature. The results revealed that stress-tolerance ability was not limited to any particular phylogenetic group. Knowledge about the genetic variants of phosphate-solubilizing fluorescent Pseudomonas with potential for tolerance to desiccation, alkalinity, temperature, and salinity could be useful in understanding their ecological role under stressful environments of low phosphate availability.     

Quantum Well Energetics of an n = 2 Ruddlesden–Popper Phase Perovskite

A comprehensive investigation of the electronic energy levels of an n = 2 Ruddlesden–Popper phase perovskite is presented. Ultraviolet and inverse photoemission spectroscopies are used to probe the density of states in the valence and conduction bands, respectively, of the quasi‐2D perovskite, butylammonium cesium lead iodide (BA₂CsPb₂I₇). By comparing experimental spectra with calculated projected density of states, the contributions from Cs, Pb, and I to the quantum well states are identified, and distinguished from those of the organic ligand barrier layer. The ionization energy, electron affinity, and exciton binding energy of this material are derived. The energetics of the quantum well structure are discussed in terms of the number of Pb‐halide layers. The resulting energy diagram suggests that a type‐I heterojunction would be formed with the n = 1 BA₂PbI₄. Finally, surface photovoltage performed via Kelvin probe force microscopy is used to evaluate band bending at the surface of the BA₂CsPb₂I₇ thin films.     

Molecular cloning and characterization of a novel glyoxalase I gene <Emphasis Type="Italic">TaGly I</Emphasis> in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Methylglyoxal is a kind of poisonous metabolite that can react with RNA, DNA and protein, which generally results in a number of side advert effects to cell. Glyoxalase I is a member of glyoxalase system that can detoxify methylglyoxal. An EST encoding a glyoxalase I was isolated from a SSH (suppression subtractive hybridization)-cDNA library of wheat spike inoculated by Fusarium graminearum. The corresponding full length gene, named TaGly I, was cloned, sequenced and characterized. Its genomic sequence consists of 2,719 bp, including seven exons and six introns, and its coding sequence is 929 bp with an open reading frame encoding 291 amino acids. Sequence alignment showed that there were two glyoxalase I domains in the deduced protein sequence. By using specific primers, TaGly I was mapped to chromosome 7D of wheat via a set of durum wheat ‘Langdon’ D-genome disomic-substitution lines. The result of Real-time quantitative polymerase chain reaction demonstrated that TaGly I was induced by the inoculation of Fusarium graminearum in wheat spikes. Additionally, it was also induced by high concentration of NaCl and ZnCl₂. When TaGly I was overexpressed in tobacco leaves via Agrobacterium tumefaciens infection, the transgenic tobacco showed stronger tolerance to ZnCl₂ stress relative to transgenic control with GFP. The above facts indicated that TaGly I might play a role in response to diverse stresses in plants.     

A New Identification Method for Aliphatic Compounds Using Linear Equations of the GC Retention Index Value

The Retention Index (I) value and the different I values from two columns, carbowax 20M (20M) and OV101 (ΔI:I_20M ? I_OV101) of aliphatic compounds were calculated by several kinds of linear equations under programmed linear temperature conditions. The equations could be used to predict appropriate compounds as well as a database of I and ΔI values.     

Lipoplexes formed from sugar-based gemini surfactants undergo a lamellar-to-micellar phase transition at acidic pH. Evidence for a non-inverted membrane-destabilizing hexagonal phase of lipoplexes

The present study aims at a better understanding of the mechanism of transfection mediated by two sugar-based gemini surfactants GS1 and GS2. Previously, these gemini surfactants have been shown to be efficient gene vectors for transfection both in vitro and in vivo. Here, using Nile Red, a solvatochromic fluorescent probe, we investigated the phase behavior of these gemini surfactants in complexes with plasmid DNA, so-called lipoplexes. We found that these lipoplexes undergo a lamellar-to-non-inverted micellar phase transition upon decreasing the pH from neutral to mildly acidic. This normal (non-inverted) phase at acidic pH is confirmed by the colloidal stability of the lipoplexes as shown by turbidity measurements. We therefore propose a normal hexagonal phase, H_I, for the gemini surfactant lipoplexes at acidic endosomal pH. Thus, we suggest that besides an inverted hexagonal (H_II) phase as reported for several transfection-potent cationic lipid systems, another type of non-inverted non-bilayer structure, different from H_II, may destabilize the endosomal membrane, necessary for cytosolic DNA delivery and ultimately, cellular transfection.     

Iodine toxicity in a plant-solution system with and without humic acid

Aqueous iodine (I_2(aq)) is a potent disinfectant that is being evaluated as a soil sanitizer for agricultural fields and a water purification treatment for the International Space Station. Rice (Oryza sativa L.) plants were grown in solution culture containing different I compounds at approximately 0, 18, or 30 μM total I [I_2(aq) + iodide (I⁻)] consisting of 0, 6, and 20 μM I as I_2(aq), respectively. In addition, humic acid (HA) was added to half the treatments. Most I_2(aq) was electrochemically reduced to the endpoint metabolite I⁻ within 24 h with HA promoting the response. Plants receiving the highest dose of I_2(aq), particularly those in treatments without HA, had the least growth and the greatest biomass I concentrations. Roots from both I_2(aq) treatments without HA were periodically sampled for bacteria. Viable and direct caints of bacterial cell density declined with increasing I_2(aq) concentrations within the first hour after treatment application. However, cell densities recovered within 96 hours and eventually surpassed the control treatment cell density. Additionally, the resulting high viable: direct count density ratio suggests that opportunistic species likely dominated the post I_2(aq) environment.     

Systematic characterisation of secondary metabolites from Ixeris sonchifolia by the combined use of HPLC‐TOFMS and HPLC‐ITMS

Introduction – Ixeris sonchifolia (Bunge) Hance, a folk medicine, has been widely used in China for its anti‐inflammatory and haemostatic effects. However, the miscellaneous component composition of this herbal medicine is not well known. Objective – To develop a fast and comprehensive analytical method for the characterisation of various components from I. Sonchifolia, as a tool for the quality control of the herb and its related preparations. Methodology – Ixeris sonchifolia samples were extracted with 60% aqueous methanol, purified by solid‐phase extraction and then analysed by the combinatorial use of HPLC‐TOFMS and HPLC‐ITMS. Results – A total of six sesquiterpene lactones, six phenolic acids and seven flavonoids were identified or tentatively characterised. Five of them were reported for the first time in I. sonchifolia and, in particular, two amino acid‐sesquiterpene lactone conjugates, 11,13‐dihydro‐13‐prolyl‐ixerin Z and 11,13‐dihydro‐13‐prolyl‐ixerin Z₁, that were first found in this plant source. Conclusion – A global profile of I. sonchifolia constituents was described, which could be useful for the quality control of this herb and its related preparations. The employed combination of HPLC‐TOFMS and HPLC‐ITMS could also be a promising tool for the analysis of other herbal medicines containing sesquiterpene lactones, phenolic acids or flavonoids. Copyright © 2010 John Wiley & Sons, Ltd.     

Irradiance influences contents of photosynthetic pigments and proteins in tropical grasses and legumes

Three tropical range grasses (Cenchrus ciliaris, Dichanthium annulatum, and Panicum antidotale) and two range legumes [Macroptilium atropurpureum (siratro) and Stylosanthes hamata (stylo)] were grown under four irradiances, i.e. 100 (I ₁₀₀, control), 75 (I ₇₅), 50 (I ₅₀), and 25 (I ₂₅) % of full sunlight. Accumulation of chlorophyll (Chl) b increased but that of Chl a decreased under low irradiances. The greater accumulation of Chl (a+b) in grasses (particularly in D. annulatum and P. antidotale) under shade predicted their shade adaptability. Among legumes Stylosanthes was more adaptive to the shade than Macroptilium due to its higher accumulation of Chl (a+b). Significant difference in the accumulation of carotenoids under I ₂₅ over I ₁₀₀ was observed in all the species, which shows the increase in quality of the fodder under limited irradiance. There was a significant decrease in soluble protein content in C. ciliaris under I ₇₅, however, no significant difference in protein content was observed under I ₅₀ and I ₂₅, which was also reflected in the SDS pattern with the reduction in content of polypeptides at I ₇₅ and following increase at I ₅₀ and I ₂₅. This was possibly due to reduction of light-induced protein at I ₇₅ and then expression of the stress-induced protein at further reduction of irradiance. Peroxidase activity in C. ciliaris increased with the decrease in irradiance and its isozyme pattern showed differences among all treatments, which indicated the role of different peroxidase isoforms at different irradiances.     

31P nuclear magnetic resonance study on changes in phosphocreatine and the intracellular pH in rat skeletal muscle during exercise at various inspired oxygen contents

We measured ATP, phosphocreatine (PCr), inorganic phosphate (P_i), and the intracellular pH in rat hindlimb muscles during submaximal isometric exercise with various O₂ deliveries using³¹P nuclear magnetic resonance spectroscopy (³¹P NMR) to evaluate changes in energy metabolism in relation to O₂ availability. Delivery of O₂ to muscles was altered by controlling the fractional concentration of inspired oxygen (F _IO₂) at 0.50, 0.28, 0.21, 0.11 and 0.08 with monitoring partial pressure of oxygen and carbon dioxide, and bicarbonate at the femoral artery. The steady-state ratio of PCr : (PCr + P_i) during exercise decreased as a function ofF _IO₂ even at 0.21. Significant acidification of the intracellular pH during exercise occurred at 0.08F _IO₂. Change in the PCr : (PCr + P_i) ratio demonstrated that the oxidative capacity, i.e. the maximal rate of the oxidative phosphorylation reaction, in muscle was not limited by O₂ delivery at 0.50F _IO₂, but was significantly limited at 0.21F _IO₂ or below. Change in the intracellular pH at 0.08F _IO₂ could be interpreted as an increase in lactate, suggesting activation of glycolysis. Correlation between the PCr : (PCr + P_i) ratio and the intracellular pH revealed the existence of a critical PCr : (PCr + P_i) ratio and pH for glycolysis activation at around 0.4 and 6.7, respectively.     

BIODIVERSITY RESEARCH: Turning up the heat: the impacts of Andropogon gayanus (gamba grass) invasion on fire behaviour in northern Australian savannas

Aim This study aimed to quantify changes in fire severity resulting from the invasion of Australia’s tropical savannas by the African grass Andropogon gayanus Kunth. (gamba grass). Location Mesic savannas of the Northern Territory, Australia. Method Byram’s fire‐line intensity (I_f), fuel load and architecture, and two post‐fire indicators of fire intensity – scorch height (SH) and char height (CH) of woody vegetation – were determined for fires in native grass savanna and A. gayanus invaded savanna. Leaf scorch is the height at which the fire’s radiant heat browns leaf tissue, and leaf char is the height that radiant heat blackens or consumes leaf tissue and provides an indirect measure of flame height. These data, and 5 years of similar data collected from the Kapalga Fire Project in Kakadu National Park, were used to develop empirical relationships between I_f and the post‐fire indices of fire intensity. Results A relationship between A. gayanus I_f and SH could not be developed because complete canopy scorch occurred in most A. gayanus fires, even at low I_f. In contrast, A. gayanus I_f was strongly correlated with CH. This empirical relationship was substantially different from that for native grass fires. For a given I_f, there was a significantly greater CH in invaded sites. This increase in radiant heat is attributable to the increased biomass (mean 3.6 t ha^?1 in native grasses compared to 11.6 t ha^?1 in A. gayanus) and height (approximately 0.5 m in native grasses compared to 4 m in A. gayanus) of the standing fine fuel. Main conclusion Andropogon gayanus invasion resulted in substantial changes in fire behaviour. This has important regional implications owing to the current (10,000–15,000 km²) and predicted (380,000 km²) area of invasion and the negative consequences for the native savanna biota that has evolved with frequent but relatively low‐intensity fire.