Tomato roots exhibit in vivo glutamate dehydrogenase aminating capacity in response to excess ammonium supply.

In higher plants ammonium (NH4+) assimilation occurs mainly through the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway. Nevertheless, when plants are exposed to stress conditions, such as excess of ammonium, the contribution of alternative routes of ammonium assimilation such as glutamate dehydrogenase (GDH) and asparagine synthetase (AS) activities might serve as detoxification mechanisms. In this work, the in vivo functions of these pathways were studied after supplying an excess of ammonium to tomato (Solanum lycopersicum L. cv. Agora Hybrid F1) roots previously adapted to grow under either nitrate or ammonium nutrition. The short-term incorporation of labelled ammonium (15NH4+) into the main amino acids was determined by GC-MS in the presence or absence of methionine sulphoximine (MSX) and azaserine (AZA), inhibitors of GS and GOGAT activities, respectively. Tomato roots were able to respond rapidly to excess ammonium by enhancing ammonium assimilation regardless of the previous nutritional regime to which the plant was adapted to grow. The assimilation of 15NH4+ could take place through pathways other than GS/GOGAT, since the inhibition of GS and GOGAT did not completely impede the incorporation of the labelled nitrogen into major amino acids. The in vivo formation of Asn by AS was shown to be exclusively Gln-dependent since the root was unable to incorporate 15NH4+ directly into Asn. On the other hand, an in vivo aminating capacity was revealed for GDH, since newly labelled Glu synthesis occurred even when GS and/or GOGAT activities were inhibited. The aminating GDH activity in tomato roots responded to an excess ammonium supply independently of the previous nutritional regime to which the plant had been subjected.

Biochar reduces the efficiency of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) mitigating N2O emissions.

Among strategies suggested to decrease agricultural soil N2O losses, the use of nitrification inhibitors such as DMPP (3,4-dimethylpyrazole phosphate) has been proposed. However, the efficiency of DMPP might be affected by soil amendments, such as biochar, which has been shown to reduce N2O emissions. This study evaluated the synergic effect of a woody biochar applied with DMPP on soil N2O emissions. A incubation study was conducted with a silt loam soil and a biochar obtained from Pinus taeda at 500 °C. Two biochar rates (0 and 2% (w/w)) and three different nitrogen treatments (unfertilized, fertilized and fertilized + DMPP) were assayed under two contrasting soil water content levels (40% and 80% of water filled pore space (WFPS)) over a 163 day incubation period. Results showed that DMPP reduced N2O emissions by reducing ammonia-oxidizing bacteria (AOB) populations and promoting the last step of denitrification (measured by the ratio nosZI + nosZII/nirS + nirK genes). Biochar mitigated N2O emissions only at 40% WFPS due to a reduction in AOB population. However, when DMPP was applied to the biochar amended soil, a counteracting effect was observed, since the N2O mitigation induced by DMPP was lower than in control soil, demonstrating that this biochar diminishes the efficiency of the DMPP both at low and high soil water contents.

Effect of N-(n-butyl) thiophosphoric triamide and 3,4 dimethylpyrazole phosphate on gaseous emissions from grasslands under different soil water contents.

The intensification of grassland systems is leading to serious environmental risks due to the large input of nitrogen (N) in fertilizers and the subsequent gaseous losses. Addition of nitrification inhibitors (NI) or urease activity inhibitors to fertilizers could reduce these losses to the atmosphere. In the present study, the effects of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) and the urease activity inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) were evaluated on NH3, N2O, NO, and CO2 emissions. Ammonium sulphate nitrate (ASN), urea and cattle slurry were applied at a rate of 70 kg N ha(-1) to a mixed clover-ryegrass sward in the Basque Country (northern Spain) under different soil water contents. NH3 and NO emissions were determined by photoacoustic and chemiluminescence respectively using an open chamber technique while N2O and CO2 emissions were measured by photoacoustic using a closed chamber technique. When the water filled pore space (WFPS) was under 60%, the application of NBPT reduced NO emissions a 34% on urea and an 18% on slurry, and the application of DMPP reduced them a 2% on ASN and a 4% on slurry. No significant effect was observed on NH3 losses. When WFPS was over 60%, no effect could be observed on NO and N2O emissions after the application of both inhibitors, but NH3 losses were reduced a 31% by NBPT when applied with the slurry. Carbon dioxide emissions were unaffected by the use of DMPP or NBPT at any soil water content. Neither grassland yield nor herbage N concentration were influenced by the application of both inhibitors.

The effect of cattle slurry electroflotation products as fertilizers on gaseous emissions and grassland yield.

The climatic conditions of the Basque Country (northern Spain) provide the favorable conditions for the growth of grasslands and the development of livestock enterprises. The intensification of the farms is leading to serious environmental risks due to the great generation of manures and slurries and their subsequent inefficient management. Their application involves N losses that can be pollutant. The environmental company ADE BIOTEC S.L. is developing the process called "electroflotation" with the aim of reducing the volume of slurries from intensive livestock farms. The process consists basically of an electrolysis of the slurry catalyzed by iron which leads to the flocculation of the solid particles, giving as a final result a solid and a liquid fraction. The objective of this work was to assess the usefulness of these two fractions as fertilizers. With this aim, the environmental risk of their application was determined regarding gaseous emissions to the atmosphere (i.e., of NO, NH(3), N(2)O, and CO(2)) and their fertilizer capacity was investigated by determining their effects on grassland yield and N uptake in comparison to the untreated slurry. The untreated slurry and the solid and the liquid fractions were all applied at a rate of 70 kg NH(4)(+)-N ha(-1). The application of the products of electroflotation did not affect N(2)O and CO(2) losses, being of the same magnitude as those caused by the application of the original slurry. However, after their application, a reduction in NH(3) volatilization losses was induced in the short term and a reduction in NO losses was caused in the long term. The solid and liquid fractions both increased biomass yield with respect to the untreated slurry. The solid fraction even induced a higher N uptake than the liquid fraction and the untreated slurry.

3,4-Dimethylpyrazol phosphate effect on nitrous oxide, nitric oxide, ammonia, and carbon dioxide emissions from grasslands.

Intensively managed grasslands are potentially a large source of NH3, N2O, and NO emissions because of the large input of nitrogen (N) in fertilizers. Addition of nitrification inhibitors (NI) to fertilizers maintains soil N in ammonium form. Consequently, N2O and NO losses are less likely to occur and the potential for N utilization is increased, and NH3 volatilization may be increased. In the present study, we evaluated the effectiveness of the nitrification inhibitor 3,4-dimethylpyrazol phosphate (DMPP) on NH3, N2O, NO, and CO2 emissions following the application of 97 kg N ha(-1) as ammonium sulfate nitrate (ASN) and 97 kg NH4+ -N ha(-1) as cattle slurry to a mixed clover-ryegrass sward in the Basque Country (northern Spain). After slurry application, 16.0 and 0.7% of the NH4+ -N applied was lost in the form of N2O and NO, respectively. The application of DMPP induced a decrease of 29 and 25% in N2O and NO emissions, respectively. After ASN application 4.6 and 2.8% of the N applied was lost as N2O and NO, respectively. The application of DMPP with ASN (as ENTEC 26; COMPO, Münster, Germany) unexpectedly did not significantly reduce N2O emissions, but induced a decrease of 44% in NO emissions. The amount of NH4+ -N lost in the form of NH3 following slurry and slurry + DMPP applications was 7.8 and 11.0%, respectively, the increase induced by DMPP not being statistically significant. Levels of CO2 emissions were unaffected in all cases by the use of DMPP. We conclude that DMPP is an efficient nitrification inhibitor to be used to reduce N2O and NO emissions from grasslands.

Middle cardiac nerve section alters ventilatory response to PaCO2 in the cockerel.

To determine whether afferents in the middle cardiac nerves (MCN) contribute to extrapulmonary PaCO2 sensitivity, we did the following: we anesthetized six cockerels with sodium pentobarbital (25-35 mg/kg), and cannulated the cutaneous ulnar vein, and the carotid and brachial arteries. The thorax was opened and each lung unidirectionally ventilated from separate gas delivery systems. A ligature, which temporarily occluded blood flow, was placed around the right pulmonary artery. Both cardiac sympathetic nerves were cut, as well as the left vagus just above the level of the recurrent branch. We exposed the non-perfused right lung to 105 Torr PCO, to silence intrapulmonary chemoreceptors (IPC). We measured blood pressure, heart rate and ventilatory movements while the denervated left lung was used to fix PaCO2 at seven levels ranging from 7-140 Torr. As arterial PCO2 increased, ventilatory amplitude increased from 0.3 mm to 3.6 mm, while frequency decreased from 140 to 24 per min. After cutting the MCN, ventilatory movements were less responsive to PaCO2 changes. Ventilatory amplitude was 3.0 mm at the lowest PaCO2 and increased to 4.0 at the highest PaCO2. We conclude that: 1) when IPC discharge is low, afferents in the MCN inhibit ventilatory movements during hypocapnia, and 2) these afferents may contribute to systemic CO2 sensitivity.

Cardiac receptors evoke ventilatory response with increased venous PCO2 at constant arterial PCO2.

The effects of elevated venous PCO2 and denervation of the cardiac ventricles on ventilation were studied in 20 anesthetized open-chest unidirectionally ventilated White Leghorn cockerels. Venous PCO2 was increased by insufflating the gut with high CO2 while recording changes in the amplitude of the sternal movements. Arterial blood gases were held constant by unidirectionally ventilating the lungs with gas flows approximately five times the animal's resting minute volume. Insufflating the gut with 90% N2-10% O2 did not change the level of ventilation, whereas with 90% CO2-10% O2 the amplitude of sternal movement increased 500% above that with no gut gas flow. Exchange of N2 for the CO2 was followed by a rapid reduction of ventilatory movements to control levels. Arterial blood gases remained constant during gut gas insufflation, whereas mixed venous PCO2 increased and mixed venous pH decreased when high CO2 was given to the gut. Cutting the middle cardiac nerves, which primarily innervate the ventricles of the heart, reduced the ventilatory response to CO2 gut insufflation by 67%. Sympathetic denervation of the thoracic viscera did not change the responses. It appears that, in the chicken, increasing the mixed venous PCO2 while holding the arterial blood gases constant alters ventilation by an afferent system located in the venous circulation or in the right ventricle which is sensitive to changes in PCO2.

The effect of hypoxia on plasma potassium concentration and the excitation of arterial chemoreceptors in the cat.

Intra-arterial recordings of potassium concentration ([K+]a) and arterial chemoreceptor discharge were made in six anaesthetized cats while tracheal PO2 was stepped every 2 min (end-tidal PO2 ca. 140, 60, 40 and 95 Torr) at constant PCO2 (33 Torr). [K+]a increased hyperbolically from 3.0 mM to 4.5 mM as arterial PO2 was lowered from 95 to 40 Torr. Because the discharge of arterial chemoreceptors is excited by hyperkalaemia as well as hypoxia, the hypoxic discharge of arterial chemoreceptors may have a component mediated by [K+]a. The mechanisms underlying the arterial K+ increase in hypoxia remain unknown.

Effects of potassium, oxygen and carbon dioxide on the steady-state discharge of cat carotid body chemoreceptors.

1. We have studied the effects of intravenous infusions of 0.1 mmol/min KCl (raising arterial potassium from ca. 3.2 to 6.0 mM) on the steady-state responses of carotid body chemoreceptors to end-tidal PCO2 and PO2 in the pentobarbitone-anaesthetized cat. 2. The excitatory effect of these KCl infusions was enhanced by hypoxia and reduced or abolished by hyperoxia. 3. Hypercapnia did not enhance, and usually reduced, excitation by KCl. 4. When similar control discharge frequencies were established by hypoxia or by hypercapnia, a KCl infusion excited the hypoxic discharge by about twice as much as it did the hypercapnic discharge. 5. These observations are not inconsistent with the idea that the mechanism underlying hypoxic excitation of arterial chemoreceptors is one that controls extracellular potassium concentration near the afferent nerve ending. 6. Insofar as potassium-induced excitation of chemoreceptor discharge is abruptly reduced by hyperoxia it behaves like Asmussen and Nielsen's postulated 'anaerobic work substance' and it may therefore contribute to the increased importance of the arterial chemoreflex reported in exercise.

Effects of altering dead space volume on respiration and air sac gases in geese.

Dead space volume (VD) was altered in spontaneously breathing, anesthetized geese from values far above (about 115 ml) to those far below (about 3 ml) the normal VD (approximately 40 ml). Respiratory gases were measured in cranial (CrS) and caudal air sacs (CdS) and in blood. The major findings were as follows: Ventilation increased linearly with VD, by increases in tidal volume (VT) at constant breathing rate (fresp); effective parabronchial ventilation, (VT-VD) X fresp, remained constant and so did arterial blood gases. No changes occurred in CrS gas composition. CdS PCO2 declined with decreasing VD, and the respiratory exchange ratio increased, reaching values above unity at the lowest VD. The gas composition in CrS, and particularly its relation to end-expired gas composition, is in agreement with current models of the gas flow pattern in the avian lung. The PCO2 values in CdS are higher than expected by simple models, e.g. by dead space re-inhalation. Neopulmonic gas exchange and incomplete gas mixing are suggested to contribute significantly to the gas composition of CdS.

Effect of acute and chronic cardiac denervation on osmotic release of vasotocin in chickens.

Hypo- and hyperosmotic NaCl were infused intravenously to examine osmotic release of arginine vasotocin (AVT) in anesthetized, acutely cardiac-denervated chickens and in conscious, chronically denervated birds. Mean arterial blood pressure was consistently higher in denervated compared to sham-operated chickens but heart rates were similar in experimental and control groups. Plasma AVT concentrations (pAVT) were significantly higher than controls in acutely, but not chronically, denervated chickens. The slope of the regression line relating pAVT to plasma sodium concentration was higher in denervated birds indicating that removal of cardiac receptor activity increases the osmotic sensitivity of the AVT system. The results suggest that cardiac end-net receptor activity may participate in the regulation of blood pressure and can modulate the release of antidiuretic hormone in the chicken.

The effect of CO2 and temperature on respiratory movements in the chicken.

We studied the effect of increasing colonic temperature (Tc) on respiratory amplitude and frequency at different levels of PICO2 in anesthetized, unidirectionally ventilated cockerels. We also evaluated the relationship between PICO2 and PaCO2. Increased PaCO2 augmented respiratory amplitude and decreased frequency at every Tc. Respiratory amplitude increased as Tc rose from 41 to 45 degrees C at each level of PaCO2. During the same rise in Tc, respiratory frequency decreased at the low PaCO2 seen in awake, panting cockerels but increased at eucapnic PaCO2. Tc had no effect on frequency at high PaCO2. Values for respiratory frequency of unidirectionally ventilated cockerels at given Tc and PaCO2 predict those of awake cockerels. We conclude that amplitude of breathing increases in acute hyperthermia unless accompanied by hypocapnia and that without hypocapnia maximal panting frequencies cannot be reached.

The alteration of CO2 respiratory sensitivity in chickens by thoracic visceral denervation.

We measured respiratory movements in nine groups of six cockerels, 20-24 weeks of age. We opened the thorax and all air sacs, and unidirectionally ventilated each lung separately. The right lung received constant P(CO2), while the P(CO2) was altered to the left lung. There were only small differences in response to P(CO2) alterations whether both pulmonary circulations were intact, the left pulmonary circulation was blocked, or the left lung was denervated and the right pulmonary circulation blocked, suggesting (1) that the extrapulonary and pulmonary P(CO2) -sensitive afferents (in one lung) have equivalent influence, and (2) the influences of the two afferent systems are not additive. Respiratory sensitivity after bilateral vagotomy is small despite pulmonary innervation by CO2 -sensitive spinal afferents, perhaps one reason for abnormal respiration after vagotomy. The respiratory influences of pulmonary vagal and spinal CO2-sensitive afferents are also non-additive, suggesting that non-additive interactions among afferents controlling respiration may be common in the chicken. Rates of response to altered intrapulmonary P(CO2) are determined by central mechanisms and not the time for CO2 distribution or receptor response.

Fiber size and sensory endings of the middle cardiac nerve of the domestic fowl (Gallus domesticus).

The middle cardiac nerve, a branch of the vagus, innervates the ventricles of the avian heart. Of 533 myelinated sensory fibers, the size range was 2 micron. The ratio of myelinated to unmyelinated sensory fibers ranged from 2.17 to 3.48. Sensory endings resembled a network pattern with no distinct receptor-like endings. Frequency of nerve population increased from apex to base of the heart.

Pulmonary circulation--vertebral venous interconnections in the chickens.

Injections of India ink colored blood, latex, and plastic followed by study of corrosion casts and dissections were used to determine the interconnections of the vertebral venous system and pulmonary circulation in the chicken. Multiple, minute connections are found to the intercostal veins, small mesenteric veins and others connected to the vertebral venous system. Thus, blood can flow in quantities between the vertebral venous system and the pulmonary circulation depending upon pressure gradients.

Nicotine-induced reflex depression of alpha motoneuron activity in the absence of fusimotor-spindle feedback.

The effects of nicotine on the stretch reflex and on electrically induced monosynaptic and cutaneous polysynaptic reflex responses at a lumbosacral level were studied in lightly anesthetized (chloralose-urethane) cats in which the regional fusimotor-spindle loops had been interrupted by ventral rhizotomy. Doses of 15-40 mug/kg injected into the superior vena cava or the right atrium produced depression of the reflex responses in extensor and flexor alpha motoneurons after latent periods of 1-3 sec, while gamma activity was initially accelerated. The early phase of this alpha depression was abolished by bilateral vagotomy. Sebacylcholine (a nicotinic agent) and acetylcholine also caused depression of evoked alpha activity in the absence of spindle feedback. It is concluded that nicotine activates a viscerosomatic reflex by exciting sensory receptors in the cardiopulmonary region and that alpha motor depression results independent of the changes in gamma activity. However, alpha depression with delayed onset can still be elicited by nicotine after vagotomy and Renshaw blockade, and this effect is also duplicated by sebacylcholine and abolished by hexamethonium. In the doses used, spindle or skin afferents were not excited by nicotine. Thus, two more mechanisms are described by which nicotine can depress alpha activity. Both are reflex in nature, one implicating vagal, the other nonvagal peripheral receptors.