Responses of nitrogen-fixing and nitrate-supplied alfalfa (Medicago sativa L.) to iron chelates in an alkaline hydroponic medium

Ferric ethylenediamine di-(o-hydroxyphenylacetate) (FeEDDHA) and ferric hydroxyethylethylenediaminetriacetic acid (FeHEDTA) were evaluated as Fe sources for hydroponic growth of alfalfa (Medicago sativa L., cv. Mesilla), either dependent on N₂ fixation or supplied with NO₃. The hydroponic medium was maintained at pH 7.5 by addition of CaCO₃. Nitrogen-fixing cultures were inoculated with Rhizobium meliloti 102 F51 and grown in medium without added nitrogen. After five to seven weeks of growth under greenhouse conditions, plants were harvested. Nitrogen fixation was measured by the acetylene reduction method.When FeEDDHA was supplied, growth of alfalfa, whether dependent on N₂ fixation or supplied with NO₃, was severely limited at concentrations typically used in hydroponic medium (10 or 20 M). Maximum yield of NO₃-supplied alfalfa was obtained at 100 M while maximum yield of N₂-fixing alfalfa was obtained in the range of 33 to 200 M FeEDDHA. Nodule fresh weights and N₂ fixation rates increased with FeEDDHA concentration up to 33 M and remained essentially constant up to 200 M. With FeHEDTA, maximum yields of both NO₃-grown and N₂-fixing alfalfa were obtained at 10 M. Growth of NO₃-supplied plants was inhibited at 200 M FeHEDTA while growth of N₂-fixing plants was inhibited at 100 M FeHEDTA. The numbers of nodules per plant increased between 3.3 and 10 M FeHEDTA; however, inhibition of nodule formation occurred at a concentration of 33 M or higher. Nodule weights per plant and N₂ fixation rates were depressed at 3.3 M as well as at 100 M FeHEDTA. The results suggest that alfalfa dependent on N₂ fixation is more sensitive to limited Fe availability than alfalfa supplied with NO₃.     

Silicon amelioration of aluminium toxicity in teosinte (Zea mays L. ssp. mexicana)

The influence of different Al concentrations, (0, 60 and 120 M Al) on growth and internal concentrations of Al, Si and selected organic acids was analysed in plants of teosinte (Zea mays L. ssp. mexicana), a wild form of maize from acid soils from Mexico. The plants were grown in nutrient solutions (pH 4.0) with or without 4 M silicon. Analysis with the GEOCHEM speciation program did not reveal differences between free activities of Al³⁺ in solutions with and without 4 M Si, but solutions with Si yielded lower concentrations of monomeric Al species, [Al]_mono, when analysed by a modified aluminon method. Plants grown on solutions with similar [Al]_mono, but differing in silicon, showed highly significant differences in growth and tissue concentrations of Al and organic acids. Silicon prevented growth inhibition at [Al]_mono concentrations as high as 35 M, while plants grown without Si suffered severe growth reductions with 33 M [Al]_mono. In solutions with similar [Al]_mono concentrations plants with Si had lower tissue Al concentrations and higher concentrations of malic acid than plants without Si. In view of both the significant influence of Si on the response of plants to Al toxicity and the fact that some soluble Si is always present in soil solutions, the addition of low Si concentrations to nutrient solutions used for Al-tolerance screening is recommended.     

The effect of monoterpenes on astaxanthin production by a mutant ofPhaffia rhodozyma

Summary The total pigment and astaxanthin content ofPhaffia rhodozyma increased with increasing concentrations -pinene up to 500 l -pinene/l. Above this concentration the total pigment and astaxanthin content as well as the biomass production decreased. The addition of 500 l -pinene/l increased the total pigment content from 1652 g/g to 2201 g/g and the astaxanthin content from 1554 g/g to 1883 g/g. A sharp decrease in maximum specific growth rate occurred above 150 l -pinene/l.     

Action of phenazine methyl sulfate,inhibitors, and uncouplers on the light-induced proton transport by cells ofRhodospirillum rubrum

Summary Suspensions of log phase cells ofRhodospirillum rubrum at pH 5.5 show a light-induced decrease in the pH of the medium which is reversed during the subsequent dark period. The velocity and magnitude of the pH change were the same whether the cells were bubbled with air, CO₂-free air or N₂ during experimentation. The pH response is temperature dependent. Phenazine methyl sulfate (PMS) at concentrations above 0.05mm stimulates the light-induced pH change. PMS at 1mm gives a 2-fold increase in the initial rate upon illumination and a 1.5-fold increase in the total change in pH after 2 min of illumination. The inhibition of the proton transport by 10 g/ml antimycin A or 20 m 2-n-heptyl-4-hydroxyquinoline-N-oxide can be partially relieved by PMS. However, inhibition of the light-induced proton transport with 0.5mm 2,4-dinitrophenol or 3 m carbonylcyanide-m-chlorophenylhydrazone (CCCP) cannot be overcome by addition of PMS. Valinomycin, at a concentration of 3 m, caused a slight stimulation of the light-induced proton transport in the presence of 200mm KCl. The inhibition of proton transport by 3 m CCCP was partially relieved with 3 m valinomycin in the presence of 200mm KCl, but the antibiotic was without effect when the cells were suspended in 200mm NaCl. The results are discussed in terms of current theories of the action of PMS, antimycin A, valinomycin, and uncouplers on the light-induced electron flow and photophosphorylation inR. rubrum.     

Comparative structure of the gas-vacuoles of blue-green algae

Summary An investigation was made of 5 species of blue-green algae reported to contain gas-vacuoles. All organisms were grown and harvested under standard conditions. Gas-vacuoles were characterised as reddish structures which are destroyed by applying pressure. Using a simple direct preparation technique gascylinders were observed with the transmission electron microscope in gas-vacuolate cells. Gas-vacuoles were present in the strains of Anabaena flos-aquae, Gloeotrichia echinulata and Oscillatoria agardhii studied and absent from Microcystis aeruginosa and Nostoc linckia. The reddish, refractile central area of N. linckia and M. aeruginosa cells was tentatively identified as nucleoplasm. Gas-vacuoles are collections of gas-cylinders 70 m wide, which in A. flos-aquae and G. echinulata are clearly bounded by photosynthetic lamellae and associated with -granules. The presence of bounding photosynthetic lamellae in these species is suggested as a causal factor of the unusual optical properties of their gas-vacuoles. The range of lengths of gas-cylinders in G. echinulata and O. agardhii is from 100 m to 500 m and in A. flos-aquae it is from 100 m to 1300 m. The percentage of cell volume occupied by gas-vacuoles was estimated by direct measurement. In A. flos-aquae and G. echinulata it was 22%. In O. agardhii gas-cylinders were not clearly associated with photosynthetic lamellae and -granules and occupied 39% of cell volume. Gascylinder membranes showed reasonable preservation in KMnO₄ and excellent preservation in OsO₄. The widths of membranes after treatment with these two fixatives was 3 m and 2 m respectively.     

Cyclic GMP-activated channels of the chick pineal gland: Effects of divalent cations,pH, and cyclic AMP

Chick pineal cells maintained in dissociated cell culture express an intrinsic photosensitive circadian oscillator, but the mechanisms of phototransduction in avian pinealocytes are not fully understood. In this study, we have used inside-out patches to examine the characteristics of cyclic GMP-activated channels of chick pinealocytes in more detail, concentrating on the effects of factors known to modulate the secretion of melatonin and/or the function of circadian pacemakers. In most patches, the predominant conductance state was 19 pS in symmetrical 145 mM NaCl. But in some patches, a second cyclic GMP-activated channel with a unitary conductance of 29 pS was also present. The current flowing through cyclic GMP-activated channels was not affected by application of salines containing 1 M Ca²⁺ to the cytoplasmic face of the patch membrane. By contrast, application of 1 mM Ca²⁺ caused a partial reduction in cyclic GMP-activated current at all membrane potentials. Application of 1–5 mM Mg²⁺ ions caused a virtually complete blockade of current at positive membrane potentials, but caused only a small decrease in current at negative membrane potentials. No obvious differences in the gating of cyclic GMP-activated channels were observed in pH 8.2, 7.4 or 6.2 salines. Application of salines containing 100 M, 500 M, or 1 mM cyclic AMP did not cause activation of the channels, but 5 mM cyclic AMP evoked a low level of channel activity. Application of 5 mM but not 100 M cyclic AMP decreased the probability of channel activation caused by 20–100 M cyclic GMP and also increased the percentage of openings to an 11 pS subconductance state. Thus, cyclic AMP acts as a weak partial agonist. Nevertheless, the gating of these channels does not seem to be controlled directly by physiologically relevant changes in intracellular Ca²⁺, pH, or cyclic AMP.     

Genetic control of ammonium transport in nitrogen fixing cyanobacterium Nostoc muscorum

Summary Ammonium (NH ₄ ⁺ ) transport was investigated in Nostoc muscorum ISU (wild type) and spontaneous mutants resistant to cyanophage N-1 (Nm/N-1), streptomycin (Nm/Sm) and methylamine (Nm/MA). N₂-fixing wild-type cells transported NH ₄ ⁺ via two transport systems: the high-affinity (K _m 11 M) and low-affinity (K _m 66 M), which formed 10 and 50-fold concentration gradients, respectively. The high-affinity system of Nm/MA (K _m 11 M) was similar to the wild type but the low-affinity system had reduced affinity for NH ₄ ⁺ (K _m 125 M), while Nm/N-1 and Nm/Sm mutants had only a high-affinity transport system (K _m 20 and 28 M, respectively). The growth of mutant Nm/N-1 was more sensitive to 1 mM NH ₄ ⁺ or methylamine than other strains, and also glutamine-synthetase activity was most reduced in NH ₄ ⁺ -grown cells. l-methionine-d, l-sulfoximine (20 M) treatment of N₂-grown Nm/N-1 cells resulted in a higher rate of NH ₄ ⁺ efflux. The apparent alterations in kinetic constants of NH ₄ ⁺ transport in mutants and glutamine synthetase activity suggested that NH ₄ ⁺ in N. muscorum is transported by specific carrier(s) and the transport is genetically controlled.     

Indole butyric acid induces regeneration of phenotypically normal apricot (Prunus armeniaca L.) plants from immature embryos

A prerequisite for most transformation systems is an efficient and reliable method to regenerate phenotypically normal plants. Immature embryos or cotyledons were cultured at three developmental stages (stage 1, 2 and 3, PF=3, 30–60, and 100, respectively) from two unrelated apricot genotypes, Zard and NJA82. Explants were cultured on MS media supplemented with either BA or TDZ at four concentrations (0, 0.5, 5.0 or 20 M) and 2,4-D at 0 or 1 M. Stage 1 embryos cultured on MS medium without growth regulators formed embryoid-like structures. Shoot primordia induction was greatest with stage 2 cotyledons on media containing 5–20 M TDZ and 1 M 2,4-D, although shoot morphology was abnormal, especially with the highest level of TDZ. In another factorial experiment, stage 2 cotyledons were cultured on media containing TDZ (0, 5, 7.5, 10, 15 or 20 M) in combination with either no auxin, 1 M 2,4-D, 1 M IBA, or 5 MIBA. Regeneration percentages of 80% or more were observed on media containing 1–5 M IBA and 5–10 M TDZ. The medium containing 5 M IBA and no TDZ exhibited the highest frequency of phenotypically normal plantlet regeneration.Abbreviations BA 6-benzylaminopurine - IBA indole-3-butyric acid - 2,4-D 2,4 dichlorophenoxyacetic acid - 2iP 2-isopentenyladenine - MS Murashige and Skoog basal medium - NAA 1-naphthaleneacetic acid - PF percent fill [(embryo length/seed length) × 100] - TDZ thidiazuron [N-phenyl-N(1,2,3,-thidiazol-5-yl)-urea] - WPM McCown's woody plant medium     

Effects of atrial natriuretic factor,nitroprusside and acetylcholine on cGMP immunostaining in the isolated perfused rat kidney

Summary In the present study the localization of the cGMP production in response to the vasodilators acetylcholine (ACh) and sodium nitroprusside (SNP) and to atrial natriuretic factor (ANF) was studied in the isolated perfused rat kidney using cGMP immunocytochemistry. After ACh (0.3 M) infusion increased cGMP immunoreactivity was found in kidney interlobar and segmental arteries and in glomeruli. SNP (1 M) and ANF (0.01 M) elevated cGMP staining in the same elements of the kidney as ACh. In the glomeruli ACh and SNP stimulated cGMP production in mesangial cells whereas ANF stimulated cGMP production in epithelial cells (podocytes). However, SNP at higher doses (10 M) stimulated cGMP production not only in glomeruli, but also in interstitial cells throughout the cortex. In addition SNP and ANF increased cGMP production in the medulla.     

AT-1 Receptor and Phospholipase C Are Involved in Angiotensin III Modulation of Hypothalamic Noradrenergic Transmission

SUMMARY 1. We previously reported that angiotensin III modulates noradrenergic neurotransmission in the hypothalamus of the rat. In the present work we studied the effects of angiotensin III on norepinephrine release and tyrosine hydroxylase activity. We also investigated the receptors and intracellular pathways involved in angiotensin III modulation of noradrenergic transmission.2. In rat hypothalamic tissue labeled with [³H]norepinephrine 1, 10, and 100 nM and 1 M losartan (AT1 receptor antagonist) had no effect on basal neuronal norepinephrine release, whereas 10 and 100 nM and 1 M losartan partially diminished norepinephrine secretion evoked by 25 mM KCl. The AT2 receptor antagonist PD 123319 showed no effect either on basal or evoked norepinephrine release. The increase in both basal and evoked norepinephrine output induced by 1 M angiotensin III was blocked by 1 M losartan, but not by 1 M PD 123319.3. The phospholipase C inhibitor 5 M neomicin inhibited the increase in basal and evoked norepinephrine release produced by 1 M angiotensin III.4. Tyrosine hydroxylase activity was increased by 1 M angiotensin III and this effect was blocked by 1 M LST and 5 M neomicin, but not by PD 123319. On the other hand, 1 M angiotensin III enhanced phosphatidyl inositol hydrolysis that was blocked by 1 M losartan and 5 M neomicin. PD 123319 (1 M) did not affect ANG III-induced phosphatidyl inositol hydrolysis enhancement.5. Our results confirm that angiotensin III acts as a modulator of noradrenergic transmission at the hypothalamic level through the AT1-phospholipase C pathway. This enhancement of hypothalamic noradrenergic activity suggests that angiotensin III may act as a central modulator of several biological processes regulated at this level by catecholamines, such as cardiovascular, endocrine, and autonomic functions as well as water and saline homeostasis.     

Two succinate uptake systems inBradyrhizobium japonicum

Succinate uptake inBradyrhizobium japonicum 61-A-101 has a biphasic kinetic, indicating the presence of a high-and low-affinity uptake system. The apparent K_M data are 2.4 M (high-affinity system) and 172 M (low-affinity system). ForEnterobacter aerogenes NCTC 10006, only one uptake system for succinate was found with an apparent K_M of 80 M. InBradyrhizobium japonicum andEnterobacter aerogenes, succinate uptake is carrier mediated and constitutive. 2,4-Dinitrophenol and cyanide severely inhibit uptake, whereas arsenate inhibits only to a lesser extent. In both strains, fumarate is also transported by the succinate uptake system. Glucose has significant effects on succinate uptake or metabolism inEnterobacter aerogenes, but not inBradyrhizobium japonicum.     

Morphology and structural organization of spiracles in femaleArgas (Persicargas) walkerae (Acari: Argasidae)

Scanning electron microscopical investigations of fractures and corrosion casts of the spiracles from femaleA. walkerae ticks revealed a four-part structure, consisting of spiracular plate, ostium and macula forming the external closure, followed by the subostial space and the vestibulum of regulable volume, as well as the atrial chamber as the innermost part from which the main tracheal trunks originate. On the average, the spiracular plate was 158 m long and 188 m at the broadest width. It consisted of a thin, highly perforated external and a thick internal layer, which enclosed the interpedicellar space with numerous stout pedicels. In its posterior region, the spiracular plate was covered by the macula, which was up to 80 m in length and 110 m in width. The interpedicellar cavity opened into the subostial space measuring 95.5 m in length and 159.6m in width, which proceeded into the 112-m long vestibulum. The roof of the vestibulum was flexible and could be everted and inverted. Inverted, the roof formed a quadratic bulge with numerous deep cuticular folds, which confined the lumen of the vestibulum either partially or completely. In corrosion casts, the roof was everted to a length of up to 89.3 m. In the posterior part of the vestibulum, as well as in the initial fourth of the artrial chamber, numerous anvil-, cone-or drop-like cuticular projections were arranged in wedge-like fashion. The atrial chamber was almost spherical with a diameter of 138.4 m. Five main tracheal trunks of different luminal diameter as well as numerous channels opened into the atrial chamber.     

SelectingRhizobium phaseoli strains for use with beans (Phaseolus vulgaris L.) in Kenya: Infectiveness and tolerance of acidity and aluminium

Forty strains ofRhizobium phaseoli, isolated from Kenyan soils, were tested for infectiveness on common bean (Phaseolus vulgaris L.). 28 strains were infective and a cultivar × Rhizobium interaction was observed. 48 strains were screened for tolerance of acidity and Al in liquid culture. Assessment of visible turbidity after 14 days indicated 34 strains tolerant of pH 4.5 but none tolerant of pH 3.5. No strain was tolerant of 50 M Al at pH 5.5. Three strains were tolerant of 20 M Al at pH 5.5 and 10 M Al at pH 4.5. Screening on a solid medium identified strains tolerant of 20 and 50 M Al at pH 5.5 and 4.5 which were sensitive to these treatments in liquid culture. Those strains tolerant to 20 M Al at pH 4.5 and 5.5 in liquid culture were correctly identified on the solid medium.     

The influence of temperature on glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and the regulation of these enzymes in a mesophilic and a thermophilic cyanobacterium

The activities and kinetics of the enzymes G6PDH (glucose-6-phosphate dehydrogenase) and 6PGDH (6-phosphogluconate dehydrogenase) from the mesophilic cyanobacterium Synechococcus 6307 and the thermophilic cyanobacterium Synechococcus 6716 are studied in relation to temperature. In Synechococcus 6307 the apparent K _m's are for G6PDH: 80M (substrate) and 20M (NADP⁺); for 6PGDH: 90M (substrate) and 25M (NADP⁺). In Synechococcus 6716 the apparent K _m's are for G6PDH: 550M (substrate) and 30M (NADP⁺); for 6PGDH: 40M (substrate) and 10M (NADP⁺). None of the K _m's is influenced by the growth temperature and only the K _m's of G6PDH for G6P are influenced by the assay temperature in both organisms. The idea that, in general, thermophilic enzymes possess a lower affinity for their substrates and co-enzymes than mesophilic enzymes is challenged.Although ATP, ribulose-1,5-bisphosphate, NADPH and pH can all influence the activities of G6PDH and 6PGDH to a certain extent (without any difference between the mesophilic and the thermophilic strain), they cannot be responsible for the total deactivation of the enzyme activities observed in the light, thus blocking the pentose phosphate pathway.Abbreviations G6PDH glucose-6-phosphate, dehydrogenase - 6PGDH 6-phosphogluconate dehydrogenase - G6P glucose-6-phosphate - 6PG 6-phosphogluconate - RUDP ribulose-1,5-bisphosphate - Tricine N-Tris (hydroxymethyl)-methylglycine     

Zinc protects against arsenic-induced apoptosis in a neuronal cell line,measured by DEVD-caspase activity

Acute and chronic arsenic exposure results in toxicity in humans and causes many neurological and other manifestations. For the first time the present study reports that zinc decreases arsenic-induced apoptosis and also confirms a single report of apoptosis induced by arsenic in a neuronal cell line. Apoptosis measured by DEVD-caspase activity peaked between 10 M and 20 M of arsenic trioxide. Higher concentrations of arsenic up to 40 M caused increasing cell death with diminishing DEVD-caspase activity. The beneficial effect of zinc was proportional to its concentration with a significant decrease in arsenic-induced DEVD-caspase activity at 50 M and 75 M zinc (P<0.05). This finding may be of therapeutic benefit in people suffering from chronic exposure to arsenic from natural sources, a global problem especially relevant to millions of people on the Indian subcontinent.     

First survey on the natural occurrence of Fusarium mycotoxins in Bulgarian wheat

Wheat for human consumption (140 samples) was collected after harvest from all regions of Bulgaria. The 1995 crop year was characterized by heavy rainfall in the spring and summer months. The internal mycoflora of wheat samples was dominated by Fusarium spp. and Alternaria spp., and storage fungi were rarely present. The samples were analysed for contamination with Fusarium mycotoxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-AcDON), 15-acetyldeoxynivalenol (15-AcDON), T-2 Toxin (T-2), diacetoxyscirpenol (DAS), and zearalenone (ZEA), using enzyme immunoassay methods. DON and ZEA were the predominant toxins, with a contamination frequency of 67% and 69%, respectively. The average levels of these toxins in positive samples were 180 g/kg (DON) and 17 g/kg (ZEA), maximum concentrations were 1800 g kg^–1 and 120 g kg^–1, respectively. Acetyl derivatives of DON, namely 3-AcDON and 15-AcDON, were found in 2.1 % and 0.7% of the samples, at at maximum level of about 100 g kg^–1. Only one sample was positive for T-2 (55 g/kg), DAS was not detected. This is the first report about the natural occurrence of a range of Fusarium mycotoxins in wheat for human consumption in Bulgaria.Abbreviations 3-AcDON 3-acetyldeoxynivalenol - 15-AcDON 15-acetyldeoxynivalenol - DAS diacetoxyscirpenol - DON deoxynivalenol - EIA enzyme immunoassay - T-2 T-2 toxin - ZEA zearalenone     

Somatic embryogenesis and plantlet regeneration from cell suspension cultures of palmarosa grass (Cymbopogon martinii)

A cell suspension culture was established from nodal callus ofCymbopogon martinii (Roxb.) Wats in a liquid medium containing Murashige and Skoog (1962) basal salts, vitamins, 100 mg 1^–1 myo-inositol and 20 g l^–1 of sucrose (MS) that was supplemented with 13.6 M 2,4-dichlorophenoxyacetic acid and 1.15 M kinetin. An initial inoculum density of 2 x 10⁴ cells ml^–1exhibited optimum cell growth. Calli were obtained 12–15 days after the suspension was plated onto semisolid medium of a similar composition. When calli were transferred to semisolid regeneration medium containing MS + 6.7 M N ⁶-benzyl-adenine + 1.15 M kinetin, somatic embryogenesis and plantlet regeneration occurred after 10–25 days. There was no significant decrease in the regeneration potential of the calli even when the cultures were initiated from 47-week-old cell suspensions. Chromosome counts of cells in suspensions, calli and somatic embryos derived from cultures of different ages revealed the presence of diploids, tetraploids and octaploids. However, the 33 regenerated plants tested were all diploid, indicating that only diploid cells were capable of regeneration in vitro.Abbreviations MS Murashige and Skoog (1962) basal salts with vitamins (100 mg1^–1 myo-inositol, 20 g1^–1 sucrose) - 2,4-D 2,4-dichlorophenoxyacetic acid - BA N ⁶-benzyl-adenine - Kn kinetin - MSC MS + 13.6 M 2,4-D + 1.15 M Kn - MSR MS +6.7 M BA + 1.15 M Kn     

Effect of thidiazuron on vegetative tissue-derived somatic embryogenesis and flowering of bamboo Bambusa edulis

Current research on somatic embryogenesis of bamboo uses reproductive tissue as explants. However, it was hard to obtain the explant. Shoots of a local accession (3–4 m high) were used for multiple shoot production. In order to obtain embryogenic callus, nodal and internodal tissues from in vitro plantlets were placed on Murashige and Skoog (MS) medium supplemented with 9.2 M kinetin (KN), 13.6 M 2,4-dichlorophenoxyacetic acid (2,4-D), 0.1% (v/v) coconut milk, and 6% (w/v) sucrose. We studied the effects of sucrose and thidiazuron (TDZ) on callus proliferation. Optimal additives to the MS medium for embryogenic callus proliferation were 0.046 M TDZ, 13.6 M 2,4-D and 3% (w/v) sucrose. TDZ also promoted the germination of bamboo somatic embryos. The germination rate of the somatic embryos exceeded 80% on MS-based medium supplemented with 0.455M TDZ. Naphthaleneacetic acid (NAA) reduced germination. Well-developed plantlets were successfully transferred to soil. There was no albino mutant in subsequent culture. In vitro regenerants and potted plants flowered, but no seeds were produced.     

Mitochondria in fine afferent nerve fibres of the knee joint in the cat: a quantitative electron-microscopical examination

The distribution of mitochondria, their content and concentration (expressed as the ratio of the mean volume of mitochondria and the surface of the sensory axon) were determined in group-III and-IV nerve fibres innervating the knee joint capsule in the cat. Mitochondria mainly accumulated in axonal swellings (beads) and end bulbs of the terminal branches. Between single nerve fibres, marked differences in the content and the concentration of mitochondria were obtained in proximal portions (inside of the perineurium) and in distal portions (unmyelinated sensory endings). In group-III nerve fibres, the mitochondrial concentration ranged from 0.005 to 0.030 m³/m² (proximal portion) and from 0.016 to 0.080 m³/m² (distal portion). In unmyelinated group-IV nerve fibres, the values also showed a broad variation ranging from 0.001 to 0.011 m³/m² (proximal portion) and from 0.003 to 0.019 m³/m² (distal portion). The wide range of mitochondrial concentrations may reflect different energy consumption during receptive processes: nerve fibres with a low mechanical threshold and a high probability of excitatory events may be rich in mitochondria, whereas fibres with a high mechanical threshold and a low probability of excitatory events may be poor in mitochondria.     

Activity of dihydrofolate reductase in the mollicutesAcholeplasma laidlawii andMycoplasma gallisepticum and their susceptibility to antifolates

Mycoplasma gallisepticum andAcholeplasma laidlawii were found to possess dihydrofolate reductases exhibiting similar specific activities and kinetics, with values in the range of those reported for other microorganisms. The apparent Km values for dihydrofolate in enzymes ofM. gallisepticum andA. laidlawii are 7.95±0.13 and 7.50±0.11 M, and for NADPNH 8.46±0.25 and 9.32±0.18 M, respectively.M. gallisepticum is 3300-fold more resistant to methotrexate than isA. laidlawii; concentrations causing 50% inhibition were 200.00 and 0.06 M, respectively. This is in contrast to almost the same sensitivity to that drug exhibited by the dihydrofolate reductases of both microorganisms.M. gallisepticum is also 3600-fold more resistant to trimethoprim than isA. laidlawii, and the concentrations for 50% inhibition of growth were 1800.0 and 0.5 M, respectively. The high resistance was found to be due partially to a 130-fold lower affinity of the target enzyme for this antifolate, but another mechanism, presumably impaired transport, must also be involved. This is the first report of dihydrofolate reductase activity in Mollicutes.