Termite Prey Specialization in the Pitcher Plant Nepenthes albomarginata--Evidence from Stable Isotope Analysis

Old World pitcher plants (Nepenthes spp., Nepenthaceae) trapand digest invertebrate prey to derive nutrients, primarilynitrogen (N). In the majority of lowland Nepenthes species studiedto date, ants (Hymenoptera, Formicidae) are numerically thedominant prey taxon. Nepenthes albomarginata is unusual in showingan apparent bias towards the capture of termites (Isoptera).We tested the hypothesis that N. albomarginata derives N fromtermite capture, by comparison of foliar stable N isotope abundance(     

Ruthenium ammine complexes as electron acceptors for growth stimulation by plasma membrane electron transport

Ammineruthenium(III) complexes have been found to act as electron acceptors for the transplasmalemma electron transport system of animal cells. The active complexes hexaammineruthenium(III), pyridine pentaammineruthenium(III), and chloropentaammineruthenium(III) range in redox potential (E ₀) from 305 to –42 mV. These compounds also act as electron acceptors for the NADH dehydrogenase of isolated plasma membranes. Stimulation of HeLa cell growth, in the absence of calf serum, by these compounds provides evidence that growth stimulation by the transplasma membrane electron transport system is not entirely based on reduction and uptake of iron.     

Influence of dose and route of administration of bovine follicular fluid and the suppressive effect of purified bovine inhibin (Mr 31,000) on plasma FSH concentrations in ovariectomized ewes

Ovariectomized Merino ewes were used to develop an in-vivo bioassay for purified bovine inhibin of Mr 31,000. Various doses (0.25, 0.5, 1 or 2 ml) of bovine follicular fluid, given either by the intravenous (i.v.) or intracarotid route (i.c.) resulted in significant linear dose-related suppression of plasma FSH and interval to maximum suppression. Control ewes (1.0 ml steer plasma) showed no significant change in FSH over the same period. Doses of 470 and 2590 U of pure inhibin given i.v. caused a significant suppression of FSH in plasma in all ewes. The in-vivo potency estimate of the high dose (2760 U, 1420-4690 fiducial limits) agreed well with the in-vitro assay of potency. There were no significant changes observed in mean plasma LH after treatment with the higher dose of pure inhibin. There were no rebound effects of treatment with bovine follicular fluid or pure inhibin on FSH concentrations above that of controls. It is concluded that the form of bovine inhibin of Mr 31,000, which is believed to be the predominant circulating form, is biologically active when administered in vivo.     

Comparison of the gonadal response of wild and laboratory field voles (Microtus agrestis) to different photoperiods

Weanling male and female field voles from laboratory stock and from the F1 generation of wild-caught animals were placed in a long (16L:8D) or short (6L:18D) photoperiod for 28 or 56 days. Both types of field vole showed the well-established effect of photoperiod upon sexual maturation, with animals in the long photoperiod having larger and more active gonads than animals in the short photoperiod. After 28 and 56 days laboratory stock females were more mature, sexually, and had a higher growth rate than did Wild F1 females. There was no difference between the two types of males at 28 days, but by 56 days laboratory stock males were more sexually mature and had a higher growth rate than did Wild F1 males. These differences between the two types occurred in the long and short photoperiods. There was no interaction between photoperiod and type of vole. The use of laboratory stock animals in experiments could lead to an incorrect assessment of the effect of photoperiod in the control of seasonal breeding in wild populations.     

Immuno-gold localization of α-L-arabinofuranosyl residues in pollen tubes of Nicotiana alata Link et otto

Immuno-gold labelling using a monoclonal antibody (PCBC3) with a primary specificity for -L-arabinofuranosyl residues was used to locate these residues in pollen tubes of Nicotiana alata grown in vivo. The antibody bound to the outer fibrillar layer of the pollen-tube wall: the inner, non-fibrillar wall layer was not labelled. Cytoplasmic vesicles (0.2 m diameter) were also labelled. The antibody may bind to an arabinan in the pollen-tube wall.     

Distribution of motoneurones innervating extraocular muscles in the brain of the marmoset (Callithrix jacchus)

Extraocular muscle motoneurones were localised in the oculomotor nucleus (ON), trochlear nucleus (TN) and abducens nucleus (AN) in the marmoset brain using the horseradish peroxidase (HRP) retrograde labelling technique. HRP pellets injected into individual extraocular muscles revealed one or more groups of labelled neurones occupying discrete loci within these nuclei. Relatively little overlap of motoneurone pools was observed, except in the case of the inferior oblique and superior rectus muscles. Injections of HRP into the medial rectus muscle revealed three separate populations of labelled cells in the ipsilateral ON. Motoneurones innervating the inferior rectus muscle were mainly localised in the lateral somatic cell column of the ipsilateral ON. A second smaller grouping was observed in the medial longitudinal fasciculus. The inferior oblique muscle motoneurones were localised in the ipsilateral medial somatic cell column intermingled with motoneurones supplying the superior rectus muscle of the opposite eye. The superior oblique muscle motoneurones occupied the entire TN and the lateral rectus muscle motoneurones the AN. It was concluded that the organisation of nuclei and subnuclei responsible for controlling the extraocular muscles in the marmoset is broadly similar to that of other primates.     

A single amino acid substitution deregulates a bacterial lactate dehydrogenase and stabilizes its tetrameric structure

We have engineered a variant of the lactate dehydrogenase enzyme from Bacillus stearothermophilus in which arginine-173 at the proposed regulatory site has been replaced by glutamine. Like the wild-type enzyme, this mutant undergoes a reversible, protein-concentration-dependent subunit assembly, from dimer to tetramer. However, the mutant tetramer is much more stable (by a factor of 400) than the wild type and is destabilized rather than stabilized by binding the allosteric regulator, fructose 1,6-biphosphate (Fru-1,6-P2). The mutation has not significantly changed the catalytic properties of the dimer (Kd NADH, Km pyruvate, Ki oxamate and kcat), but has weakened the binding of Fru-1,6-P2 to both the dimeric and tetrameric forms of the enzyme and has almost abolished any stimulatory effect. We conclude that the Arg-173 residue in the wild-type enzyme is directly involved in the binding of Fru-1,6-P2, is important for allosteric communication with the active site, and, in part, regulates the state of quaternary structure through a charge-repulsion mechanism.     

Induction of siderophore activity in Anabaena spp. and its moderation of copper toxicity.

Growth of Anabaena sp. strain 7120 (in the absence of chelators or added iron) was inhibited by the addition of 2.1 to 6.5 microM copper and was abolished by copper concentration of 10 microM or higher. When the copper was chelated to schizokinen (the siderophore produced by this organism in response to iron starvation), the toxic effects were eliminated. Analysis of culture filtrates showed that the cupric schizokinen remains in the medium, thereby lowering the amount of copper taken up by the cells. Although this organism actively transports ferric schizokinen, it apparently does not recognize the cupric complex. Thus, Anabaena sp. is protected from copper toxicity under conditions in which siderophore is being produced. For cells grown in low iron, the accumulation of extracellular schizokinen was observed to parallel cell growth and continue well into stationary phase. The actual iron status of the organism was monitored by using iron uptake velocity as an assay. Cultures grown on 0.1 microM added iron were found to be severely iron limited upon reaching stationary phase, thus explaining the continued production of schizokinen. These data show that the siderophore system in Anabaena spp. has developed primarily as a response to iron starvation and that additional functions such as alleviation of copper toxicity or allelopathic inhibition of other algal species are merely secondary benefits.     

Rational construction of a 2-hydroxyacid dehydrogenase with new substrate specificity

Using site-directed mutagenesis on the lactate dehydrogenase gene from Bacillus stearothermophilus, three amino acid substitutions have been made at sites in the enzyme which we suggest in part determine specificity toward different hydroxyacids (R-CHOH-COOH). To change the preferred substrates from the pyruvate/lactate pair (R = -CH3) to the oxaloacetate/malate pair (R = -CH2-COO-), the volume of the active site was increased (thr 246----gly), an acid was neutralized (asp-197----asn) and a base was introduced (gln-102 - greater than arg). The wild type enzyme has a catalytic specificity for pyruvate over oxaloacetate of 1000 whereas the triple mutant has a specificity for oxaloacetate over pyruvate of 500. Despite the severity and extent of these active site alterations, the malate dehydrogenase so produced retains a reasonably fast catalytic rate constant (20 s-1 for oxaloacetate reduction) and is still allosterically controlled by fructose-1,6-bisphosphate.     

Age-related changes in testicular development and reproductive endocrinology associated with aflatoxicosis in the male chicken

A study was conducted to investigate endocrine and testicular changes in the male chicken associated with the ingestion of 10 or 20 ppm aflatoxin at 3 different stages of development. Weekly body weight gain, absolute and relative combined testes weights, and plasma testosterone concentrations were reduced in aflatoxin-fed males as compared to controls, with the greatest differences seen at 12 wk of age. The effect of dietary aflatoxin on levels of plasma luteinizing hormone (LH) was dependent on age at exposure. Concentrations of plasma LH in 6-wk-old control males were significantly higher than in aflatoxin-fed birds, whereas no treatment differences were observed in older males. Additionally, few changes were observed in static levels of monoamines in any of the brain regions assayed, regardless of age at exposure. The delay in peak levels of LH, as well as the suppression of plasma testosterone and testicular weight, indicate a possible delay in the onset of sexual maturation associated with aflatoxicosis in this species.