Heterogeneity of the calcium-dependent phosphatidylinositol phosphodiesterase in rat brain

1. The Ca²⁺-dependent phosphatidylinositol phosphodiesterase (phospholipase C-type) from the cytosolic supernatant of rat brain was active against exogenous [³²P]-phosphatidylinositol from pH5.0 to pH8.5. However, the activity in the range pH7.0–8.5 could not be recovered after precipitation with (NH₄)₂SO₄; most of the enzyme activity was recovered in the 30–50% fraction and showed a single sharp pH optimum at 5.5. 2. The cytosolic supernatant was analysed by isoelectric focusing on acrylamide gels, and assay at pH5.5. Four peaks of phosphodiesterase activity were found at pI ranges 7.4–7.2, 6.0–5.8, 4.8–4.4 and 4.2–3.8. 3. The cytosolic supernatant was also applied to a chromatofocusing column, and again assayed at pH5.5. Four peaks were eluted: minor, but consistent, activity at the beginning of the elution with a pI of near 7.2 or above; a second peak at pH6.0–5.85; a third broad peak with a wide range pH5.3–4.2; and a fourth peak, which was eluted by washing the column with 1m-NaCl, suggesting an isoenzyme with a pI below 4.0 (supported by the result of the isoelectric focusing). 4. If all the chromatofocusing fractions were assayed at pH7.0 or 8.0 (at 1mm-Ca²⁺), only a single sharp peak was detected, with a pI of 4.6–4.8. This peak disappeared on (NH₄)₂SO₄ fractionation (30–50%) of the cytosolic supernatant, whereas the four peaks with activity at pH5.5 were virtually unaffected. 5. The four activities (assayed at pH5.5) separated by chromatofocusing produced inositol 1:2-cyclic monophosphate, inositol 1-monophosphate and diacylglycerol as enzymic products. 6. We conclude that the Ca²⁺-dependent phosphatidylinositol phosphodiesterase exhibits considerable heterogeneity, both with respect to pH optima of activity, and its isoelectric properties.     

Epidemiology of wheat take-all as influenced by soil pH and temporal changes in inorganic soil N

Summary Soil pH, NH ₄ ⁺ and NO ₃ ⁻ concentrations in soil, and take-all root rot of winter wheat grown in the field were measured concurrently from sowing to anthesis in order to relate disease development to liming and N fertilization practices. Experimental variables included soil pH (5.5 and 6.0) and three N sources (NH₄NO₃, (NH₄)₂SO₄, NH₄Cl) banded with the seed at sowing in factorial combination with the same three N sources topdressed in the spring. Take-all severity was increased by increasing soil pH and by fertilization with NO ₃ ⁻ . Disease severity on crown roots increased exponentially following spring N fertilization and was affected more by soil pH and N-form than was severity on seminal roots. Grain yield ranged from 4.70 Mgha⁻¹ with spring NH₄NO₃ at soil pH 6.0 to 7.65 Mgha⁻¹ with spring NH₄Cl at soil pH 5.5. Sixty-six percent of the variability in grain yield was explained by the number of take-all infected crown roots per tiller at anthesis. Oregon Agric. Exp. Stn. technical paper no. 7707.     

Microbiological Survey of Adirondack Lakes with Various pH Values

Nine high-altitude oligotrophic Adirondack lakes in upstate New York having water of pH 4.3 to 7.0 were surveyed for total bacterial numbers and possible adaptation of the microbial communities to environmental pH. The number of heterotrophic bacteria from water samples recoverable on standard plate count agar were low (10¹ to 10³ per ml) for most of the lakes. Acridine orange direct counts were approximately two orders of magnitude higher than plate counts for each lake. Sediment aerobic heterotrophs recovered on standard plate count agar ranged from 1.4 × 10⁴ to 1.3 × 10⁶ per g of sediment. Direct epifluorescence counts of bacteria in sediment samples ranged from 3.0 × 10⁶ to 1.4 × 10⁷ per g. Low density values were consistent with the oligotrophic nature of all the lakes surveyed. There were no apparent differences in numbers of bacteria originally isolated at pH 5.0 and pH 7.0 between circumneutral lakes (pH > 6.0) and acidic lakes (pH < 5.0). Approximately 1,200 isolates were recultured over a range of pH from 3.0 to 7.0. Regardless of the original isolation pH (pH 5.0 or pH 7.0), less than 10% of the isolates grew at pH < 5.0. Those originally isolated at pH 5.0 also grew at pH 6.0 and 7.0. Those originally isolated at pH 7.0 preferred pH 7.0, with 98% able to grow at pH 6.0 and 44% able to grow at pH 5.0. A chi-square contingency test clearly showed (P < 0.005) that two distinct heterotrophic populations had been originally isolated at pH 5.0 and pH 7.0, although there is undoubtedly some overlap between the two populations.     

Growth and nutrient uptake of sorghum cultivated with vesicular-arbuscular mycorrhiza isolates at varying pH

This study was conducted to determine the effects of different pH regimes on root colonization with four vesicular-arbuscular mycorrhiza (VAM) isolates, and VAM effects on host plant growth and nutrient uptake. Sorghum [Sorghum bicolor (L.) Moench] was grown at pH 4.0, 5.0, 6.0 and 7.0 (±0.1) in hydroponic sand culture with the VAM isolates Glomus etunicatum UT316 (isolate E), G. intraradices UT143 (isolate I), G. intraradices UT126 (isolate B), and an unknown Glomus isolate with no INVAM number (isolate A). Colonization of roots with the different VAM isolates varied differentially with pH. As pH increased, root colonization increased with isolates B and E, remained unchanged with isolate I, and was low at pH 4.0 and high at pH 5.0, 6.0, and 7.0 with isolate A. Isolates E and I were more effective than isolates A and B in promoting plant growth irrespective of pH. Root colonization with VAM appeared to be independent of dry matter yields or dry matter yield responsiveness (dry matter produced by VAM compared to nonmycorrhizal plants). Dry matter yield responsiveness values were higher in plants whose roots were colonized with isolates E and I than with isolates A and B. Shoot P concentrations were lower in plants colonized with isolates E and I than with isolates A and B or nonmycorrhizal plants. This was probably due to the dilution effect of the higher dry matter yields. Neither the VAM isolate nor pH had an effect on shoot Ca, Mg, Zn, Cu, and Mn concentrations, while the VAM isolate affected not only P but also S, K, and Fe concentrations. The pH x VAM interaction was significant for shoot K, Mg, and Cu concentrations.     

Effect of pH on growth and ethanol production byZymomonas

Summary In a mineral salts medium containing yeast extract, NH₄Cl and glucose (50g/L), the pH range producing the fastest growth ofZ. mobilis was 5.5–6.5 with an apparent optimum at 6.5. At constant growth rate of 0.15hr^–1, the specific rates of glucose utilization (q_s) and ethanol production (q_p) were relatively unaffected by pH over the range 7.0–5.5 but increased sharply as the pH was further decreased below 5.5 to 4.0. Under these conditions the ethanol yield was unaffected by pH over the range 4.0–6.5 but decreased markedly at pH of 7.     

The sealed storage of moist flax with and without the use of chemical preservatives

The suitability of ensilage as a means of preserving flax was investigated in a series of experiments in which 400 kg round bales of fresh flax were sealed in polyethylene film or plastic wrapped, with or without the addition of formic acid at 2.5 litre t^-1 or formalin at 5.6 litre t^-1 at the time of baling. Plastic wrapping provided a more effective seal than the bags which were easily punctured by the flax roots resulting in moulding and deterioration of the flax. Where the seal was not broken untreated flax underwent a clostridial fermentation and the pH fell to about 4.8. Cellulolytic activity degraded the flax fibre over a period of 3 to 6 months. The addition of formic acid reduced the cellulolytic activity provided the seal was not broken. In an experiment with 4 kg batches of flax of 65%, 40% or 25% MC sealed in polyethylene film, the addition of formic or propionic acids at 20 g kg^-1 DM did not prevent moulding and deterioration, but both NH₃ and SO₂ at 40 g kg^-1 DM preserved the physical structure of the flax. The NH₃ darkened the flax and made it pliable and unscutchable while the SO₂ bleached it and preserved the fibre without microbiological deterioration. The presence of acids on the moist stored flax appeared to inhibit the progress of normal water retting.     

Acid and Neutral Hydrolases in Trypanosoma cruzi. Characterization and Assay*

Twelve acid hydrolases, 4 near-neutral hydrolases and alkaline phosphatase were demonstrated in 0.34 M sucrose homogenates of Trypanosoma cruzi strain Y: p-nitrophenylphosphatase and α-naphthylphosphatase, with optimum pH at ? 6.0; α-galactosidase, β-galactosidase, β-glucosidase, N-acetyl-β-glucosaminidase, cathepsin A and peptidase I and III, with optimum pH between 5.0 and 6.0: and arylsulfatase cathepsin D, α-arabinase and α-mannosidase with optimum pH at ? 4.0 α-Glucosidase, gluccse-6-phosphatase and peptidase II had optimum pH at ? 7.0. β-Glycerophcsphatase had a broad pH-activity curve from 4.0 to 7.4, with maximum activity at pH 7.0. The main kinetic characteristics of these enzymes and their quantitative assay methods were studied. No activity was detected for α-fucosidase, β-xylosidase, β-glucuronidase, elaidate esterase. acid lipase, and alkaline phospho-diesterase.     

New Culture Medium Containing Ionic Concentrations of Nutrients Similar to Concentrations Found in the Soil Solution

A new growth medium which closely approximates the composition of the soil solution is presented. This soil solution equivalent (SSE) medium contains the following components (millimolar): NO₃, 2.5; NH₄, 2.5; HPO₄, 0.005; Na, 2.5; Ca, 4.0; Mg, 2.0; K, 0.503; Cl, 4.0; SO₄, 5.0; ethylenediamine-di(o-hydroxyphenylacetic acid), 0.02; and MES [2-(N-morpholino)ethanesulfonic acid] (to maintain the pH at 6.0), 10, plus 0.1% arabinose. The advantages of the SSE medium are discussed.     

THE OPTIMUM PH OF FOUR STRAINS OF ACIDOPHILIC SNOW ALGAE IN THE GENUS CHLOROMONAS (CHLOROPHYTA) AND POSSIBLE EFFECTS OF ACID PRECIPITATION1

Four axenic strains of snow algae were examined for optimum pH under laboratory conditions using M-1 growth medium. Growth was measured using cell counts, cell measurements and absorbance readings at 440 nm. Strains C204 and C479A of Chloromonas sp. from the Adirondack Mountains, New York, grew optimally at pH 4.0 to 5.0. Strains C381F and C381G, Chloromonas polyptera (Fritsch) Hoh., Mull. & Roem. from the White Mountains, Arizona, grew optimally at pH 4.5 to 5.0. Growth was significantly higher at pH 4.0 in the northeastern species (Chloromonas sp.), but no significant difference was observed in final growth at pH 4.5, 5.0 and 5.5 between species. It is postulated that the more acidic precipitation in the northeastern United States may be selecting for strains of snow algae with greater tolerance to acidity than in strains from the southwestern United States or that the different pH optima reported are simply species differences. New York strain C204 was also grown in heavily buffered AM medium where it had an optimum pH of 5.0, but cells became irregularly shaped and tended to clump at pH 6.0 to 7.0. Growth of C204 in AM medium was significantly lower than in M-1 medium for snow algae. These findings justify the use of M-1 medium for this type of experimentation.     

Isolation, Purification, and Some Properties of Penicillium chrysogenum Tannase

Tannase isolated from Penicillium chrysogenum was purified 24-fold with 18.5% recovery after ammonium sulfate precipitation, DEAE-cellulose column chromatography, and Sephadex G-200 gel filtration. Optimum enzyme activity was recorded at pH 5.0 to 6.0 and at 30 to 40°C. The enzyme was stable up to 30°C and within the pH range of 4.0 to 6.5. The K_m value was found to be 0.48 × 10⁻⁴ M when tannic acid was used as the substrate. Metal salts at 20 mM inhibited the enzyme to different levels.     

Differential pH restoration after ammonia-elicited vacuolar alkalisation in rice and maize root hairs as measured by fluorescence ratio

Changes of vacuolar pH in hair cells of young rice (Oryza sativa L.) and maize (Zea mays L.) roots were measured after ammonia application at various levels of external pH. After loading the pH-sensitive, fluorescent dye Oregon green 488 carboxylic acid 6-isomer into the vacuoles of root hairs, ratiometric pH data of high statistical significance were obtained from root hair populations comprising hundreds of cells. The pH of the vacuole at external pH 5.0 was 5.32 ± 0.08 (±SD, n= 15) and 5.41 ± 0.13 (±SD, n= 15) in rice and maize, respectively. A moderate external ammonia concentration of 2 mM led to vacuolar alkalisation at both, low (pH 5.0) and high (pH 7.0–9.0) external pH, presumably due to NH₃ permeation into the vacuole. With increasing external pH, ammonia application did not cumulatively increase vacuolar pH. In rice, the increase in vacuolar pH ranged from 0.1–0.8 pH units; in maize a more constant increase of 0.5 pH units was observed. The vacuolar pH increase was efficiently depressed in rice (especially at high external pH), but not in maize. Inhibition of the tonoplast H⁺-ATPase by concanamycin A raised vacuolar pH and increased the ammonia-elicited vacuolar alkalisation in both species, proving that vacuolar H⁺-ATPase activity counters the ammonia-elicited alkalisation effect. However, even under conditions of vacuolar H⁺-ATPase inhibition, rice was still able to restore an ammonia-elicited pH increase. High vacuolar pH levels as found in maize under conditions of high NH₃ influx may derive from inefficient cytosolic ammonia assimilation and tonoplast proton pumping. Thus, in maize, prolonged reduction of the proton gradient between the cytosol and the vacuole may play an important role in NH₃ toxicity. Received: 12 September 1997 / Accepted: 19 January 1998     

H2 production from chemostat fermentation of glucose byClostridium butyricum andClostridium pasteurianum in ammonium- and phosphate limitation

Summary In ammonium-limitation (4.55 mM NH₄ ⁺) at a dilution rate (D)=0.081 h^–1,Clostridium butyricum produced 2 mol H₂ per mol glucose consumed at pH 5.0, but at a low fermentation rate. At higher pH, important amounts of extracellular protein were produced. Phosphatelimitation (0.5 mM PO₄ ^–3) at D=0.061 h^–1 and pH 7.0 were the best conditions tested for hydrogen gas production (2.22 mol H₂ per mol glucose consumed) at a high fermentation rate. Steady-state growth at lower pH and with 0.1 mM PO₄ ^–3 resulted in proportional higher glucose incorporation into biomass and lower H₂ production. C. pasteurianum in NH₄ ⁺ limitation showed higher fermentation rates thanC. butyricum and a stabilized H₂ production around 2.08 (±0.06) mol per mol glucose consumed at various defined pH conditions, although the acetate/butyrate ratio increased to 1 at pH 7.0. The latter was also observed in phosphate-limitation, but here H₂ production was maximal (1.90 mol. per mol glucose consumed) at the lowest pH (5.5) tested.     

Field decomposition of transgenic Bt maize residue and the impact on non-target soil invertebrates

The release of chemical compounds from plant roots that suppress soil nitrification is termed biological nitrification inhibition (BNI). Determining the environmental factors that control the synthesis and release of BNI-compounds from Brachiaria humidicola (Rendle) Schweick, a tropical pasture grass that thrives on acid soils, is the focus of this investigation. Because the BNI trait is related to the N status of the plant, we investigated the possibility that the expression of this trait would be related to the forms of N found in the root environment. Plants were grown with two sources of N, NH₄⁺ or NO₃⁻ for 60 days and the release of BNI-compounds monitored. Only plants grown with NH₄⁺ released BNI-compounds from roots. The presence of NH₄⁺ and possibly the secondary effect of its uptake (i.e., acidic pH) in the root environment significantly enhanced the release of BNI-compounds. Both the NH₄⁺ and NO₃⁻ grown plants responded to the stimulus from NH₄⁺ in the root environment. BNI-compounds found in root tissue and their release were nearly three times greater in NH₄⁺ grown than from NO₃⁻ grown plants. The BNI-compounds released from roots composed of at least three active components—Type-I (stable to pH changes from 3.0 to 10), Type-II (temporarily loses its inhibitory effect at a pH higher than a threshold pH of 4.5 and the inhibitory effect is reestablished when the root exudate pH is adjusted to <4.5) and Type-III (inhibitory effect is irreversibly lost if the pH of the root exudate reaches 10.0 or above). A major portion of BNI-compounds released in the presence of NH₄⁺ is of Type-I. In the absence of NH₄⁺, mostly Type-II and Type-III BNI-compounds were released. The BNI-compounds inhibited the function of Nitrosomonas europaea through the blocking of both ammonia monooxygenase and hydroxylamino oxidoreductase pathways. These results indicate that the release of BNI-compounds from B. humidicola roots is a regulated function and that presence of NH₄⁺ in the root environment is necessary for the sustained synthesis and release of BNI.     

Effect of pH and buffer on butyric acid production and microbial community characteristics in bioconversion of rice straw with undefined mixed culture

This study was conducted to identify the optimum pH range and the appropriate buffer for butyric acid production from rice straw by fermentation using an undefined mixed culture. A series of experiments conducted at pH levels of 5.0 ~ 7.0 showed that neutral pH improved rice straw conversion and consequently carboxylic acid production. The highest butyric acid production (up to 6.7 g/L) was achieved at pH of 6.0 ~ 6.5, while it was only 1.7 g/L without pH control or at pH 5.0. Another series of experiments conducted at pH 6.0 ~ 6.5 buffered with CaCO₃, NaHCO₃, NH₄HCO₃ and their combinations indicated that different buffers had different effects onthe product spectrum, and that CaCO₃ combined with NaHCO₃ was an effective buffer for butyric acid production. The highest total volatile fatty acids (about 12.6 g/L) production and one of the two highest butyric acid concentrations (about 7.6 g/L) were obtained by buffering with CaCO₃ combined with NaHCO₃. PCR-DGGE analysis revealed that different pH and buffers also influenced the microbial population distribution. Bacteria were suppressed at low pH, while the bacterial community structures at higher pH varied slightly. Overall, this study presents an alternative method for butyric acid production from lignocellulosic biomass without supplementary cellulolytic enzyme.     

Effects of NO2 − or NO3 − supply on polyamine accumulation and ethylene production of wheat roots at acidic and neutral pH: implications for root growth

Exposure of plant tissues to nitrite ion or nitrite-derived NO at acidic pH results in the degradation of important macromolecules and may lead to the formation of reactive molecular species. Polyamines as free radical scavengers protect plant tissues against membrane and DNA damage during stress and may contribute to the acclimation processes caused by nitrite as an abiotic stressor at acidic pH. The putrescine content of wheat roots grown under low salt conditions increased only transiently at pH 7.0 when the nutrient solution was replaced by 1mM KNO₂, KNO₃, NaNO₂ or NaNO₃, but the concentration of this diamine remained high after a 24-hour incubation at pH 4.0. The acid stress-induced putrescine accumulation was further enhanced by an external N source, especially by nitrite. The contents of spermine and spermidine in the 24-hour samples were also higher in N-supplied roots at acidic pH. Polyamine contents were not closely correlated with the ethylene production by the intact roots. Nitrite treatment, however, significantly decreased the ethylene release from the root apex, but not from the basal parts at pH 4.0. The peroxidative capacities of the tissues in the soluble fractions were also inhibited by nitrite in the apical zones, which might modify the H₂O₂-coupled oxidative processes. Nitrite ion at acidic pH may react directly with guaiacol-like phenolic compounds and in this way interfere with the lignification process. The low ethylene release by the apical zones in acidic environment may be a symptom of the nitrite-induced inhibition of root extension.     

Production and properties of fibrinolytic enzyme fromStreptomyces sp. NRC 411

Of 16Streptomyces spp. investigated for the production of extracellular fibrinolytic enzyme, one species was chosen as the most promising producer. Using shaken cultures grown for 7 days, optimal conditions for enzyme production were pH 6.0, 5% (w/v) starch as carbon source, (NH₄)₂SO₄ and soybean flour as nitrogen sources and KH₂PO₄ at 1.2 g/l. Maximal activity of the crude enzyme was at pH 6.0 and 45°C. Holding the enzyme at 37°C for 2 h decreased the activity by only 10%.     

Preparation of Ultrafiltered Rice Bran Extract and Some Factors Affecting its Browning Inhibition in Potato Puree

Abstract

Rice bran extract (RBE) was fractionated by using ultrafiltration techniques. The obtained retentate (R) inhibited the browning of potato puree to a similar extent as RBE and more than it's permeate. The R that was incubated at pH 4.0, 5.0, and 6.0 inhibited the browning of potato puree more than R that was incubated at pH 7.0 or 8.0. Potato puree that was treated with heated R at 80°C for 10 min had a browning value similar to that of puree treated with unheated R and lower than those treated with heated R at 40 or 60°C for 10 min.     

Modulation of maize roots H+-ATPase by sulfated polysaccharides

Vesicles derived from maize roots retain a membrane bound H⁺-ATPase that is able to pump H⁺ at the expense of ATP hydrolysis. In this work it is shown that heparin, fucose-branched chondroitin sulfate and dextran sulfate 8000 promote a shift of the H⁺-ATPase optimum pH from 6.0 to 7.0. This shift is a result of a dual effect of the sulfated polysaccharides, inhibition at pH 6.0 and activation at pH 7.O. At pH 6.0 dextran 8000 promotes an increase of the apparent K_m for ATP from 0.28 to 0.95 mM and a decrease of the V_max from 14.5 to 7.1 mol P_i/mg · 30 min^–1. At pH 7.0 dextran 8000 promotes an increase in V_max from 6.7 to 11.7 mol Pi/mg · 30 min^–1. In the presence of lysophosphatidylcholine the inhibitory effect of the sulfated polysaccharides observed at pH 6.0 was not altered but the activation of pH 7.0 decreased. It was found that in the presence of sulfated polysaccharides the ATPase became highly sensitive to K⁺ and Na⁺. Both the inhibition at pH 6.0 and the activation promoted by the polysaccharide were antagonized by monovalent cations (K⁺>Na⁺Li⁺).Abbreviations Mops 4-morpholinopropanesulfonic acid - EDTA ethylenediaminetetraacetic acid - ACMA 9-amino-6-chloro-2-methoxyacridine - FCCP carbonyl cyanide p(trifluoromethoxy)-phenylhyrazone     

Determination of lamotrigine in human serum by liquid chromatography

A rapid high-performance liquid chromatographic method was developed using a short silica column (30 mm×4.6 mm) with an aqueous methanol mobile phase consisting of methanol–water–NH₄H₂PO₄ (94:5.96:0.04) adjusted to a final apparent pH of 5.0 and pumped at a flow-rate of 1 ml/min. Ultraviolet detection was carried out at a wavelength of 280 nm, and serum samples were prepared for HPLC analysis by extraction into dichloromethane after basification. Lamotrigine was eluted at 0.96 min. Within-day variation of the method was 4.46% at 0.75 μg/ml and 2.37% at 6.0 μg/ml, and day-to-day variation was 9.10% at 0.75 μg/ml and 7.28% at 6.0 μg/ml.     

Biological nitrification inhibition (BNI) activity in sorghum and its characterization

Aims

The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI). Here, we aimed at the quantification and characterization of the BNI function in sorghum that includes inhibitor production, their chemical identity, functionality and factors regulating their release.

Methods

Sorghum was grown in solution culture and root exudate was collected using aerated NH₄Cl solutions. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the BNI activity. Activity-guided chromatographic fractionation was used to isolate biological nitrification inhibitors (BNIs). The chemical structure was analyzed using NMR and mass spectrometry; pH-stat systems were deployed to analyze the role of rhizosphere pH on BNIs release.

Results

Sorghum roots released two categories of BNIs: hydrophilic- and hydrophobic-BNIs. The release rates for hydrophilic- and hydrophobic- BNIs ranged from 10 to 25 ATU?g^?1 root dwt. d^?1. Addition of hydrophilic BNIs (10 ATU?g^?1 soil) significantly inhibited soil nitrification (40 % inhibition) during a 30-d incubation test. Two BNI compounds isolated are: sakuranetin (ED₈₀ 0.6 μM; isolated from hydrophilic-BNIs fraction) and sorgoleone (ED₈₀ 13.0 μM; isolated from hydrophobic-BNIs fraction), which inhibited Nitrosomonas by blocking AMO and HAO enzymatic pathways. The BNIs release required the presence of NH ₄ ⁺ in the root environment and the stimulatory effect of NH ₄ ⁺ lasted 24 h. Unlike the hydrophobic-BNIs, the release of hydrophilic-BNIs declined at a rhizosphere pH >5.0; nearly 80 % of hydrophilic-BNI release was suppressed at pH ≥7.0. The released hydrophilic-BNIs were functionally stable within a pH range of 5.0 to 9.0. Sakuranetin showed a stronger inhibitory activity (ED₅₀ 0.2 μM) than methyl 3-(4-hydroxyphenyl) propionate (MHPP) (ED₅₀ 100 μM) (isolated from hydrophilic-BNIs fraction) in the in vitro culture-bioassay, but the activity was non-functional and ineffective in the soil-assay.

Conclusions

There is an urgent need to identify sorghum genetic stocks with high potential to release functional-BNIs for suppressing nitrification and to improve nitrogen use efficiency in sorghum-based production systems.