The lepidopteran mitochondrial control region: structure and evolution

For several species of lepidoptera, most of the approximately 350-bp mitochondrial control-region sequences were determined. Six of these species are in one genus, Jalmenus; are closely related; and are believed to have undergone recent rapid speciation. Recent speciation was supported by the observation of low interspecific sequence divergence. Thus, no useful phylogeny could be constructed for the genus. Despite a surprising conservation of control-region length, there was little conservation of primary sequences either among the three lepidopteran genera or between lepidoptera and Drosophila. Analysis of secondary structure indicated only one possible feature in common--inferred stem loops with higher-than-random folding energies-- although the positions of the structures in different species were unrelated to regions of primary sequence similarity. We suggest that the conserved, short length of control regions is related to the observed lack of heteroplasmy in lepidopteran mitochondrial genomes. In addition, determination of flanking sequences for one Jalmenus species indicated (i) only weak support for the available model of insect 12S rRNA structure and (ii) that tRNA translocation is a frequent event in the evolution of insect mitochondrial genomes.      

Ferric Leghemoglobin in Plant-Attached Leguminous Nodules

Leghemoglobin (Lb) is essential for nitrogen fixation by intact leguminous nodules. To determine whether ferric Lb (Lb3+) was detectable in nodules under normal or stressed conditions, we monitored the status of Lb in intact nodules attached to sweet clover (Melilotus officinalis) and soybean (Glycine max [L.] Merr.) roots exposed to various conditions. The effects of N2 and O2 streams and elevated nicotinate levels on root-attached nodules were tested to determine whether the spectrophotometric technique was showing the predicted responses of Lb. The soybean and sweet clover nodules' Lb spectra indicated predominantly ferrous Lb and LbO2 in young (34 d) plants. As the nodule aged beyond 45 d, it was possible to induce Lb3+ with a 100% O2 stream (15 min). At 65 d without inducement, the nodule Lb status indicated the presence of some Lb3+ along with ferrous Lb and oxyferrous Lb. Nicotinate and fluoride were used as ligands to identify Lb3+. Computer-calculated difference spectra were used to demonstrate the changes in Lb spectra under different conditions. Some conditions that increased absorbance in the 626 nm region (indicating Lb3+ accumulation) were root-fed ascorbate and dehydroascorbate, plant exposure to darkness, and nodule water immersion.     

T cell receptor-mediated Ca2+ signaling: Release and influx are independent events linked to different Ca2+ entry pathways in the plasma membrane

In this study, we showed that cross-linking CD3 molecules on the T cell surface resulted in Ca²⁺ release from the intracellular stores followed by a sustained Ca²⁺ influx. Inhibition of release with TMB-8 did not block the influx. However, inhibition of phospholipase C activity suppressed both Ca²⁺ release and influx. Once activated, the influx pathway remained open in the absence of further hydrolysis of PIP2. Thapsigargin, a microsomal Ca²⁺ -ATPase inhibitor, stimulated Ca²⁺ entry into the cells by a mechanism other than emptying Ca²⁺ stores. In addition, Ca²⁺ entry into the Ca²⁺ -depleted cells was stimulated by low basal level of cytosolic Ca²⁺, not by the emptying of intracellular Ca²⁺ stores. Both the Ca²⁺ release and influx were dependent on high and low concentrations of extracellular Ca²⁺. At low concentrations, Mn²⁺ entered the cell through the Ca²⁺ influx pathway and quenched the sustained phase of fluorescence; whereas, at higher Mn²⁺ concentration both the transient and the sustained phases of fluorescence were quenched. Moreover, Ca²⁺ release was inhibited by low concentrations of Ni²⁺, La³⁺, and EGTA, while Ca²⁺ influx was inhibited by high concentrations. Thus, in T cells Ca²⁺ influx occurs independently of IP3-dependent Ca²⁺ release. However, some other PIP2 hydrolysis-dependent event was involved in prolonged activation of Ca²⁺ influx. Extracellular Ca²⁺ influenced Ca²⁺ release and influx through the action of two plasma membrane Ca²⁺ entry pathways with different pharmacological and biochemical properties.     

Effect of a membrane interactive peptide on plant cells of canola (Brassica napus) and two fungal pathogens

Summary A membrane interactive peptide was toxic to microspores, pollen and protoplasts of canola in the 1–5 µM concentration range. Similarly, at 5.0 µM the peptide completely inhibited germination of conidia ofVerticillium albo-atrum; however, when tested with conidia of a virulent isolate of blackleg (Leptosphaeria maculens), a fungal pathogen of canola, much higher levels (>30 µM) of the peptide were required to reduce or arrest germination and growth of the conidia. When testing the relative toxicities of novel peptides on plant cells and their pathogens, pollen germination is a simple, rapid and reliable alternative to protoplasts.     

Some adaptations between Danaus plexippus and its food plant, with notes on Danaus chrysippus and Euploea core (Insecta: Lepidoptera)

Behaviour of the egg-laying Monarch in captivity suggests that the concentration and quality of cardiac glycosides in the food plant are not important oviposition cues. The presence of eggs (as previously noted by Urquhart, 1960) and larvae feeding on the food plant, act as mild deterrents.
The butterfly's emetic potency (see Table XIII(a)) can sometimes surpass that of the leaves of the host plant itself. Unidentified factors, providing the internal plant environment, are more important as cardiac glycoside storage stimulants than either the quantity or quality of the cardenolides present. In the laboratory D. plexippus oviposited preferentially on a plant with relatively low cardiac glycoside content, but which produced the most powerfully protected (emetic) adult.
Metabolic changes during the pharate pupal stage, but also, in the case of Euploea core , in the larval fifth instar, rather than larval sequestration, may account for the major increase or decrease in butterfly toxicity compared with that of the food plant.
Temperature does not affect the storage of cardenolides except indirectly by altering metabolic rate. There is no evidence to support the concept that current "physiological cost" of cardenolide storage is high. Like the toad, this butterfly can be assumed to have evolved an enzvmatic system well adjusted to the presence of cardenolides in its bodv tissues.     

Biosynthesis and localization of lactate dehydrogenase X in pachytene spermatocytes and spermatids of mouse testes

The presence and biosynthesis of the testis-specific isozyme of lactate dehydrogenase (LDH-X) in cells at various stages of spermatogenesis have been examined. Enrichment of testicular cells in various stages of spermatogenesis has been achieved by two methods: (1) cell separation by velocity sedimentation in the Elutriator rotor and (2) γ irradiation of testes to eliminate specific classes of testicular cells. Separation of cells from immature mice indicated that cells prior to the midpachytene stage contain no LDH-X. Measurement of LDH-X levels in cells separated from adult mice and in testicular homogenates prepared at various times after irradiation indicated that the highest level of LDH-X per cell (normalized for DNA content) was in spermatids. Synthesis of LDH-X was determined, after in vivo injection of [³H]valine, by measurement of the radioactivity in LDH-X precipitated with specific antiserum. After irradiation, the rate of LDH-X synthesis remained constant, despite the loss of early primary spermatocytes. In separated cells, the rate of LDH-X synthesis was highest in late pachytene spermatocytes, lower in round spermatids, and even lower, but still significant, in elongated spermatids. Therefore, the synthesis of LDH-X begins at a specific point during spermatogenesis, the midpachytene stage of spermatocyte development, and continues throughout spermatid differentiation.     

Effects on Sperm Morphology by Alleles at the Pink-Eyed Dilution Locus in Mice

Sperm head morphology was analyzed in all genotypic combinations for alleles dark pink-eye (p^d) and p-sterile alleles, p^6H, p^bs (p -black-eyed sterile) and p^25H. Three of these, p^6H, p^bs and p^25H, were radiation induced; homozygotes and heterozygotes of these three alleles are male sterile, whereas p^d/— genotypes are fertile. Sperm heads were examined by light microscopy and assigned to one of five classes: A. normal and near-normal, B. triangulate and oblate, C. spatulate, D. elongate, and E. filamentous. Males of each sterile genotype had grossly abnormal sperm and each sterile genotype differed from all other sterile genotypes and from fertile genotypes in at least one class, except p^6H/p^6H compared to p^bs/p^bs.Frequency distribution profiles (1) revealed a complex pattern of allelic interaction and do not support a deletion-complementation hypothesis, (2) do not show simple bimodality, which might suggest post-meiotic (haploid) gene expression, and (3) together with unpublished breeding data, show that p^25H is not a remutation of p^6H.     

Isolation and characterization of a polynucleotide phosphorylase from Bacillus amyloliquefaciens.

Bacillus amyloliquefaciens BaM-2 produces large amounts of extracellular enzymes, and the synthesis of these proteins appears to be dependent upon abnormal ribonucleic acid metabolism. A polynucleotide phosphorylase (nucleoside diphosphate:polynucleotide nucleotidyl transferase) was identified, purified, and characterized from this strain. The purification scheme involved cell disruption, phase partitioning, differential (NH4)2SO4 solubilities, agarose gel filtration, and diethylaminoethyl-Sephadex chromatography. The purified enzyme demonstrated the reactions characteristic of polynucleotide phosphorylase: polymerization, phosphorolysis, and inorganic phosphate exchange with the beta-phosphate of a nucleotide diphosphate. The enzyme was apparently primer independent and required a divalent cation. The reactions for the synthesis of the homopolyribonucleotides, (A)n and (G)n, were optimized with respect to pH and divalent cation concentration. The enzyme is sensitive to inhibition by phosphate ion and heparin and is partially inhibited by rifamycin SV and synthetic polynucleotides.