Role of magnesium in combination with liming in alleviating acid-soil stress with the aluminium-sensitive sorghum genotype CV323

An experiment to study the effects of Mg nutrition on root and shoot development of the Al-sensitive sorghum (Sorghum bicolor (L.) Moench) genotype CV323 grown in pots of sandy loam under different acid soil stress is reported. This experiment had a factorial design: four rates of liming were combined with four rates of Mg fertilization. When no Mg was added, the pH of the soil solutions (collected in ceramic cups) increased from 4.0 (unlimed) to 4.2, 4.7 and 5.9 at the increasing rates of liming. After 30 days of growth dry matter yields of the limed treatments were 40%, 115% and 199% higher than that of the unlimed treatment. Without liming and at the highest liming rate, adding Mg did not affect plant biomass significantly. At the two intermediate levels of liming, however, 11.3 mg extra Mg per kg soil increased dry matter yield to the same levels as found at the highest liming rate. Concentrations of Mg in the soil solution rose after Mg was added and fell when lime was added, but adding both Mg and lime increased Mg concentrations in the plant shoots. In plants of the limed treatments, dry matter yield was correlated closely with the Mg concentration in the shoot. This was not so in the unlimed treatment. Furthermore, in the unlimed treatments root development was inhibited, but reduced Mg uptake by the plants resulted mainly from the direct effect of Al- (or H-) ions in the soil solution rather than from impaired root development. It is concluded that Mg fertilization counteracted the interfering effects of Al- and H ions on Mg uptake.     

What limits nitrate uptake from soil?

Abstract. An accepted view, that unless nitrate concentrations in the soil solution are very low (e.g. below 0.1–0.2 mol m^?3) the growth of high-yielding crops is not limited by the availability of nitrogen, is challenged. Conventional analyses of nutrient supply and demand, based on calculations of apparent inflow rates (uptake rates per unit total root length) are invalid. Apparent inflow rates are inversely proportional to root length. The convention of using total root length grossly overestimates the fraction of the root system active in nutrient uptake. Consequently, inflow rates based on total root lengths underestimate the true values, indicating unrealistically low nutrient concentration differentials between bulk soil and root surfaces required to drive uptake. An alternative method of analysis is suggested. This is based on total nutrient uptake rather than on inflow rate. Measurements of the former do not depend on estimates of active root length and can be made directly and reliably. The method was applied to data obtained from a pot experiment using spring wheat (Triticum aestivum L., cv. Wembley) grown in soil without nitrogen fertilizer (N₀) or with nitrogen fertilizer equivalent to 200kg N ha^?1 (N⁺). Soil nitrate concentrations calculated using the conventional method based on total root length, suggested that any increases in concentration above those measured in the N⁰ treatment should not have resulted in increased uptake and growth. However, the N⁺ plants were always bigger than those in the No treatment, refuting this suggestion. Theoretical uptakes of nitrogen (calculated initially on the basis of a fully active root system) were adjusted, by reducing the effective root length incrementally, until the theoretical uptake matched the measured net uptake of nitrogen. The mean fractions of the root systems likely to have been involved in nitrate uptake were 11% and 3.5% of the total lengths of root in the N⁰ and N⁺ treatments, respectively.     

Alterations in cardiac function and subcellular membrane activities after hypervitaminosis D3

The present study was designed to induce massive accumulation of calcium in the myocardium and to evaluate the effect of calcium overload on myocardial contractile function and biochemical activity of cardiac subcellular membranes. Rats were treated with an oral administration of 500,000 units/kg of vitamin D₃ for 3 consecutive days, and their hearts were sampled on the 5th day for biochemical analysis. On the 4th and 5th days, heart rate, mean aortic pressure, left ventricular systolic pressure and left ventricular dP/dt were significantly lowered in vitamin D₃-treated rats, demonstrating the existence of appreciable myocardial contractile dysfunction. Marked increases in the myocardial calcium (67-fold increase) and mitochondrial calcium contents (24-fold increase) were observed by hypervitaminosis D3. Mitochondrial oxidative phosphorylation and ATPase activity were significantly reduced by this treatment. A decline in sarcolemmal Na⁺, K⁺-ATPase activity was also observed, while relatively minor or insignificant changes in calcium uptake and ATPase activities of sarcoplasmic reticulum were detectable. Electron microscopic examination revealed calcium deposits in the mitochondria after vitamin D₃ treatment. The results suggest that hypervitaminosis D₃ produces massive accumulation of calcium in the myocardium, particularly in the cardiac mitochondrial membrane, which may induce an impairment in the mitochondrial function and eventually may lead to a failure in the cardiac contractile function.     

Putrescine uptake regulation in response to alpha-difluoromethylornithine treatment in Leishmania infantum promastigotes

Summary The putrescine uptake/efflux regulation and their regulatory role on intracellular polyamine pools have been studied in the parasitic protozoa Leishmania infantum. Putrescine uptake was age-dependent with maximal values in logarithmic phase promastigotes and minimal in stationary phase. Moreover, putrescine uptake was activated in response to depletion of intracellular polyamines by alpha-difluoromethylornithine (DFMO) — a well known irreversible enzyme-activated inhibitor of ornithine decarboxylase. Kinetic studies of putrescine uptake induction showed a notable rise in Vmax without Km changes, suggesting a de novo synthesis of putrescine carriers. Putrescine uptake was able to replenish polyamine content and also to recover the proliferative rate in cells treated during 24 hours with DFMO.     

Effect of lowered muscle temperature on the physiological response to exercise in men

The effect of low muscle temperature on the response to dynamic exercise was studied in six healthy men who performed 42 min of exercise on a cycle ergometer at an intensity of 70% of their maximal O2 uptake. Experiments were performed under control conditions, i.e. from rest at room temperature, and following 45 min standing with legs immersed in a water bath at 12 degrees C. The water bath reduced quadriceps muscle temperature (at 3 cm depth) from 36.4 (SD 0.5) degrees C to 30.5 (SD 1.7) degrees C. Following cooling, exercise heart rate was initially lower, the mean difference ranged from 13 (SD 4) beats.min-1 after 6 min of exercise, to 4 (SD 2) beats.min-1 after 24 min of exercise. Steady-state oxygen uptake was consistently higher (0.2 l.min-1). However, no difference could be discerned in the kinetics of oxygen uptake at the onset of exercise. During exercise after cooling a significantly higher peak value was found for the blood lactate concentration compared to that under control conditions. The peak values were both reached after approximately 9 min of exercise. After 42 min of exercise the blood lactate concentrations did not differ significantly, indicating a faster rate of removal during exercise after cooling. We interpreted these observations as reflecting a relatively higher level of muscle hypoxia at the onset of exercise as a consequence of a cold-induced vasoconstriction. The elevated steady-state oxygen uptake may in part have been accounted for by the energetic costs of removal of the extra lactate released into the blood consequent upon initial tissue hypoxia.     

High-affinity [3H]inositol uptake by dissociated brain cells and cultured fibroblasts from fetal mice

The accumulation of [³H]inositol by mechanically dissociated brain cells and cultured skin fibroblasts from fetal mice was examined. Uptake by both tissues was strongly dependent on temperature and the presence of sodium ions. Brain and fibroblast uptake also responded similarly to inhibition by inositol isomers and phloridzin. At lower concentrations of inositol, both tissues exhibited high-affinity uptake kinetics with apparent K_m values near 30 M, similar to values observed previously in human fibroblasts and other cultured cells. The activity of brain high-affinity uptake was nearly an order of magnitude lower than that of fibroblasts, however, and was in part confounded by the presence of a low-affinity or simple diffusion system operating at inositol concentrations above 100M. Brain preparation from adult mice also showed evidence of high-affinity, Na⁺ dependent uptake, but its activity was significantly diminished relative to that of fetal brain preparations. Our results demonstrate that a high-affinity inositol transport system closely resembling that found in cultured cells is expressed in the developing mouse brain.     

Stimulation of Amino Acid Uptake and Na+, K+-ATPase Activity by Norepinephrine in Superior Cervical Sympathetic Ganglia Excised from Adult Rats

Active uptake of a labelled nonmetabolizable amino acid, alpha-aminoisobutyric acid (AIB), into isolated superior cervical sympathetic ganglia (SCG) excised from adult rats was considerably stimulated by the addition of either norepinephrine (NE, 50 microM) or 3,4-dihydroxyphenylethylamine (dopamine, DA, 100 microM) to the medium during aerobic incubation for 2 h at 37 degrees C. The NE-induced increase in AIB uptake was significantly antagonized by the addition of an alpha 1-adrenoceptor antagonist (prazosin, 10 microM) in SCG axotomized 1 week prior to the examination, in which most of the ganglionic neurons had degenerated and reactive proliferation of the satellite glial components was in progress. The addition of neither acetylcholine (ACh, 1 mM) plus eserine (0.1 mM) nor cyclic nucleotides (1 mM) changed the AIB uptake by the SCG. In the axotomized SCG, the NE-evoked increase in AIB uptake was much more pronounced than that of intact or denervated SCG. A kinetic study of the active AIB uptake in the SCG showed that NE produced a decrease of the Km value and an increase in the Vmax, especially in the axotomized SCG. Ganglionic Na+, K+-ATPase activity was greatly stimulated in the presence of NE, but not by ACh. These results strongly suggest that the NE-induced enhancement of active AIB uptake in the isolated SCG is occurring in glial cells rather than in neuronal cells, with a possible alteration of membrane properties for amino acid uptake and with an apparent regulation by the stimulated transport enzyme Na+, K+-ATPase.     

Studies on a Possible Functional Coupling Between Presynaptic Acetylcholinesterase and High-Affinity Choline Uptake in the Rat Brain

The relationships between presynaptic acetylcholinesterase (AChE) and high-affinity choline uptake (HACU) were investigated using a monolayer of rat cortex synaptosomes in superfusion conditions. The following sets of experiments were performed: determination of [3H]choline ([3H]Ch) uptake during superfusion with [3H]Ch; determination of [3H]Ch uptake during superfusion with acetylcholine (ACh) tritiated in the Ch moiety; evaluation of ACh hydrolysis during superfusion with ACh labelled in the acetate moiety; and comparison of the uptake of [3H]Ch generated by hydrolysis of [3H]ACh with that occurring during superfusion with [3H]Ch. Intact ACh was not taken up by superfused synaptosomes. The uptake of [3H]Ch during superfusion with 1 or 0.1 microM [N-methyl-3H]ACh was two-thirds of that occurring during superfusion with the same concentrations of [3H]Ch. The amount of [3H]Ch produced by hydrolysis during 16 min of superfusion was 1/25 of the amount passing through the synaptosomal monolayer during 16 min of superfusion with [3H]Ch. The results indicate that presynaptic AChE and HACU are located in close proximity to each other on the cholinergic terminal membrane, an observation suggesting the possibility of a functional coupling between the two mechanisms.