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.     

Influence of various soil factors on the effects of ferulic acid on leaf expansion of cucumber seedlings

Summary Cucumber seedlings were grown in a Portsmouth soil-sand system to study how varying soil clay and organic matter content might modify cucumber seedling response to ferulic acid, a reported allelopathic agent. Leaf area expansion of cucumber seedlings, soil respiration, and soil solution concentrations of ferulic acid were monitored. Leaf area, mean absolute rates of leaf expansion, and shoot dry weight of cucumber seedlings were significantly reduced by ferulic acid concentrations ranging from 10 to 70 μg/g dry soil. Ferulic acid was applied every other day, since it rapidly disappeared from soil solution as a result of retention by soil particles, utilization by microbes and/or uptake by roots. The amount of ferulic acid retained (i.e., adsorbed, polymerized,etc.) by soil particles appeared to be secondary to microbial utilization and/or uptake by roots. Varying clay (5.3 to 9.8 g/cup) and organic matter (2.0 to 0.04g/cup) contents of the soil appeared to have little impact on the disappearance of ferulic acid from soil solution under “ideal” growth conditions for cucumber seedlings unless larger amounts of ferulic acid were added to the soil; in this case 200 μg/g. The addition of ferulic acid to the soil materials substantially increased the activity of the soil microbes. This latter conclusion is based on recovery of ferulic acid from soil solution and soil respiration measurements. Paper No. 10347 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, N C 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the product named, nor criticism of similar ones not mentioned.     

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.     

The history and chronology of siwalik cercopithecids

Cercopithecid monkeys make a comparatively late appearance in the Miocene Siwalik formations of the Indian Subcontinent. The oldest well-dated specimen is a 6.3 MY old colobine, ?Presbytis sivalensis, and it is doubtful that any cercopithecids were present in the Siwalik faunas prior to 7.0 MY, a date that is considerably later than estimates for their appearance elsewhere in Eurasia. Cercopithecines appear later than colobines. Although their temporal ranges are uncertain, cercopithecines evidently were not present before 3.2 MY and possibly not until 2.5 MY. They are represented by three species,?Macaca palaeindica, Procynocephalus subhimalayanus, andTheropithecus delsoni. In the Siwaliks the appearances of colobines and cercopithecines coincide with or follow shortly after major faunal changes that also bring other northern Eurasian and African taxa into the region.     

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.     

Steroid feedback inhibition of pulsatile secretion of gonadotropin-releasing hormone in the ewe

The long-term negative feedback effects of sustained elevations in circulating estradiol and progesterone on the pulsatile secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) were evaluated in the ewe following ovariectomy during the mid-late anestrous and early breeding seasons. GnRH secretion was monitored in serial samples of hypophyseal portal blood. Steroids were administered from the time of ovariectomy by s.c. Silastic implants, which maintained plasma concentrations of estradiol and progesterone at levels resembling those that circulate during the mid-luteal phase of the estrous cycle; control ewes did not receive steroidal replacement. Analysis of hormonal pulse patterns in serial samples during 6-h periods on Days 8-10 after ovariectomy disclosed discrete, concurrent pulses of GnRH in hypothalamo-hypophyseal portal blood and LH in peripheral blood of untreated ovariectomized ewes. These pulses occurred every 97 min on the average. Treatment with either estradiol or progesterone greatly diminished or abolished detectable pulsatile secretion of GnRH and LH, infrequent pulses being evident in only 3 of 19 steroid-treated ewes. No major seasonal difference was observed in GnRH or LH pulse patterns in any group of ewes. Our findings in the ovariectomized ewe provide direct support for the conclusion that the negative-feedback effects of estradiol and progesterone on gonadotropin secretion in the ewe include an action on the brain and a consequent inhibition of pulsatile GnRH secretion.     

Pituitary receptors for gonadotropin-releasing hormone in relation to changes in pituitary and plasma luteinizing hormone in ovariectomized-hypothalamo pituitary disconnected ewes. I. Effect of changing frequency of gonadotropin-releasing hormone pulses

Studies were undertaken to determine if changes in the amplitude of luteinizing hormone (LH) pulses that occur in response to changes in the frequency of gonadotropin-releasing hormone (GnRH) pulses are due to an alteration in the number of GnRH receptors. Ewes were ovariectomized (OVX) and the hypothalamus was disconnected from the pituitary (HPD). Ewes were then given pulses of GnRH at a frequency of 1/h or 1/3 h. Two control groups were included: OVX ewes not subjected to HPD, and HPD ewes that were not OVX. At the end of one week of treatment, blood samples were collected to determine the amplitude of LH pulses. The treated ewes were killed just before the next scheduled pulse of GnRH, and the content of LH and number of GnRH receptors were measured in each pituitary. The amplitude of LH pulses was highly correlated with the amount of LH in the pituitary gland (r = 0.71, p less than 0.01), and both LH content and pulse amplitude (mean + SEM) were higher in ewes receiving GnRH once per 3 h (189.7 +/- 39.3 microgram/pituitary, 10.3 +/- 1.1 ng/ml, respectively) than in ewes receiving GnRH once per h (77.8 +/- 11.4 microgram/pituitary, 5.2 +/- 1.3 ng/ml). The pituitary content of LH was highest in the OVX ewes (260.2 +/- 57.4 micrograms/pituitary) and lowest in the nonpulsed HPD ewes (61.7 +/- 51.2 micrograms/pituitary). The number of GnRH receptors was similar in all groups, and was not correlated with any other variable.(ABSTRACT TRUNCATED AT 250 WORDS)