Interspecific pollen competition as a reproductive barrier between sympatric species of Helianthus (Asteraceae)

Artificial crosses between Helianthus annuus and H. petiolaris using 1:9, 1:1, and 9:1 mixtures of intraspecific: interspecific pollen were conducted to determine the role of interspecific pollen competition as a reproductive barrier in Helianthus. Of 1,245 achenes analyzed from the pollen competition experiments, only 49 were hybrids. The number of hybrids observed was significantly less than expectations for all three pollen mixtures, regardless of the identity of maternal parent (P < 0.01). Stigma age and pollen ratio had no significant impact on hybrid frequency. However, hybrids were significantly more frequent with H. annuus than with H. petiolaris as the maternal parent (P < 0.01). Analysis of pollen tube growth rates revealed no differences in the rate of growth of intraspecific vs. interspecific pollen. Likewise, pollinations with either intraspecific or interspecific pollen or with different pollen ratios did not affect the percentage of filled achenes. Thus, the mechanism responsible for selective fertilization by intraspecific pollen in mixed pollen loads remains unclear. Nonetheless, these findings suggest that interspecific pollen competition plays an important role in controlling the formation of hybrids between H. annuus and H. petiolaris and may partially account for patterns or differential cytoplasmic vs. nuclear introgression in Helianthus.     

Interactions of galactose-binding lectins with plant protoplasts

Summary Protoplasts isolated from cell suspension cultures of carrot (Daucus carota L.) and leaves of tobacco (Nicotiana tabacum L.) were treated with three lectins specific for galactosyl residues. After incubation with RCA I (Ricinus communis agglutinin, molecular weight 120,000) conjugated to ferritin or fluorescein, freshly isolated protoplasts displayed heavy labeling of their surfaces. Moreover, they agglutinated rapidly when exposed to low concentrations of RCA I. In parallel studies, PNA (peanut agglutinin) also bound extensively to the protoplast plasma membranes whileBandeiraea simplicifolia lectin I attached relatively weakly. When protoplasts were cultured for two days and then incubated with conjugates of RCA I and PNA, additional binding sites were revealed on the regenerating walls.The results indicate that galactosyl residues are distributed densely over the surface of plant protoplasts. They also allow inferences to be made regarding the positions and linkages of the galactose groups being recognized by the lectins. Moreover, they open up the question whether the galactosyl moieties detected in the wall derive from those labeled on the plasma membrane. To conclude, we make comparisons with binding by concanavalin A, and predict that galactose-recognizing lectins will join and in certain respects prove superior to concanavalin A as probes of the plant cell surface.     

Sexual preferences of male hamsters (Mesocricetus auratus) for conspecifics in different endocrine conditions

The behavioral responses of sexually experienced male hamsters toward a pair of anesthetized conspecifics were investigated. Males spent significantly more time licking, sniffing, and mounting neonatally and adult castrated males than intact males. Adult castrated males receiving oil injections were preferred over castrates receiving exogenous testosterone propionate (TP). Ovariectomized females were preferred over intact males, adult castrated males, or spayed females receiving exogenous TP. It was concluded that the absence of an androgen-dependent factor(s) renders an animal more sexually attractive.     

Measurement and analysis of gas exchange during exercise using a programmable calculator

Although exercise testing is useful in the diagnosis and management of cardiovascular and pulmonary diseases, a rapid comprehensive method for measurement of ventilation and gas exchange has been limited to expensive complex computer-based systems. We devised a relatively inexpensive, technically simple, and clinically oriented exercise system built around a desktop calculator. This system automatically collects and analyzes data on a breath-by-breath basis. Our calculator system overcomes the potential inaccuracies of gas exchange measurement due to water vapor dilution and mismatching of expired flow and gas concentrations. We found no difference between the calculator-derived minute ventilation, CO2 production, O2 consumption, and respiratory exchange ratio and the values determined from simultaneous mixed expired gas collections in 30 constant-work-rate exercise studies. Both tabular and graphic displays of minute ventilation, CO2 production, O2 consumption, respiratory exchange ratio, heart rate, end-tidal O2 tension, end-tidal CO2 tension, and arterial blood gas value are included for aid in the interpretation of clinical exercise tests.     

Comparison of the properties of detergent-solubilized NADPH-cytochrome P-450 reductases from pig liver and kidney immunochemical,kinetic, and reconstitutive properties

NADPH-cytochrome P-450 reductases from pig liver and kidney and rabbit liver microsomes were purified to a specific activity of 50–62 μmol cytochrome c reduced/min/mg. All reductase preparations were separated into one major and one minor fraction on Sephadex G-200 columns. The molecular weights of the major fractions of the reductases were estimated to be 74,000, 75,000, and 75,500 for rabbit liver, pig kidney, and liver reductases, respectively, whereas the molecular weight of the minor fractions of these reductases, 67,000, was the same as that of the steapsin-solubilized pig liver reductase on SDS-polyacrylamide gel electrophoresis. K_m values for NADPH and cytochrome c were: 20 and 29 μm or 14 and 28 μm for the pig kidney or liver reductase, respectively. Immunochemical studies, including Ouchterlony double diffusion experiments and inhibition of benzphetamine N-demethylation activity in microsomes by antibody against pig liver NADPH-cytochrome P-450 reductase, indicated the similarity of the purified liver and kidney reductases. There were no differences in the ability to reconstitute NADPH-mediated benzphetamine N-demethylation and laurate hydroxylation in reconstituted systems between the pig liver and kidney reductases, indicating that the reductase did not determine substrate specificity in these systems.     

Radical mechanism of aminopyrine oxidation by cumene hydroperoxide catalyzed by purified liver microsomal cytochrome P-450

Under identical experimental conditions, purified preparations of rabbit liver microsomal cytochrome P-450 and beef heart metmyoglobin were equally effective at stimulating the oxidation of aminopyrine to a free radical species by cumene hydroperoxide. Mannitol had no effect on radical levels produced with either hemeprotein-hydroperoxide system; however, specific ligands of the two hemeproteins, substrates of cytochrome P-450, and phospholipid affected the two systems quite differently. Only the metmyo-globindependent oxidation of aminopyrine was significantly inhibited by fluoride and cyanide. Metyrapone, a specific ligand of cytochrome P-450, and benzphetamine, which was N-demethylated by cumene hydroperoxide only in the presence of cytochrome P-450, inhibited only the cytochrome P-450-stimulated oxidation of aminopyrine. Moreover, only with the solubilized liver hemeprotein was aminopyrine radical generation markedly stimulated by phospholipid. Similar properties of aminopyrine N-demethylation and radical formation by the cytochrome P-450-cumene hydroperoxide system have strongly implicated the radical as a requisite intermediate in product formation. Micromolar concentrations of metyrapone caused parallel inhibition, by at least 50%, of both radical generation and formaldehyde production. These results support a radical pathway of N-demethylation proposed for other hemeprotein-hydroperoxide systems (B. W. Griffin and P. L. Ting, 1978, Biochemistry, 17, 2206–2211), in which the substrate undergoes two successive one-electron abstractions, followed by hydrolysis of the iminium cation intermediate. Thus, for this class of substrates, the experimental data are consistent with the oxygen atom of the product arising from H₂O and not directly from the hydroperoxide, which has been previously proposed as a general mechanism for cytochrome P-450 peroxidatic activities.     

Recombination and Chromosome Segregation during the Single Division Meiosis in SPO12–1 and SPO13–1 Diploids

This paper reports a study of chromosome segregation and recombination during sporulation of spo12–1 and spo13–1 diploid strains of S. cerevisiae. These strains undergo a single division to form asci containing two diploid or near-diploid spores. The segregation of centromere-linked markers in the two-spored (dyad) products indicates that the division is generally equational. However, in a small percentage of the spo12–1 and spo13–1 cells, it appears that a meiosis I-like division occurs. Aberrant segregation of the MAT locus on chromosome III, yielding a monosomic and a trisomic spore pair, occurs in 12% of all dyads. The segregation patterns of markers at various distances from their centromeres and several pairs of markers on the same chromosome indicate that recombination takes place in both strains at nearly standard meiotic levels.     

Ultrastructural observations on the cell surface of the intestinal epithelium of the nematode,Ascaris suum

Summary The intestinal epithelium of Ascaris suum consists of a single layer of tall columnar epithelial cells that rest on a thick basal membrane in contact with the pseudocoelomic cavity. Experiments were conducted on glutaraldehyde-fixed tissue to ascertain the nature of the electronegative charges associated with both the apical microvillar surface and basal membrane.A strong electronegative charge was demonstrated on the microvillar surface and basal membrane with ruthenium red and cationic ferritin staining. The ionic nature of ferritin binding was demonstrated with poly-L-lysine, a polycation that interacts with anionic groups on the membrane and thus blocks the subsequent binding of ferritin. Tissue thus treated was devoid of reaction product. Methylation with diazomethane completely abolished staining. Since the stronger acidic groups of sulfates or phosphates would not be protonated under the conditions employed in this study, and therefore susceptible to methylation, staining by ferritin is thought to be due to its interaction with carboxyl groups. Prior enzymatic treatment of tissue with neuraminidase or phospholipase C had no effect on subsequent ferritin binding. Tissue exposed to colloidal iron at various pH values showed maximal reactivity at a pH of 2.5 or above. Above pH 2.5, the dissociation of protons from free carboxyl groups of protein-bound amino-acid residues with pK's of 3.8 and 4.2 would be maximal, and the ionized carboxyl groups are then available to interact with iron micelles. These results suggest the presence of weaker acidic groups, such as the carboxyl groups of acidic amino acids or uronic acid residues. The stronger acidic groups of sialic acid and the esterified sulfate groups, if present, contribute only minimally to overall staining. These results demonstrate that a high electronegative charge density exists, despite the apparent lack of sialic acid. Staining is believed to be due to carboxyl groups of acidic amino acids and/or carboxyl groups or uronic acid residues.Part of this work was conducted at the Department of Zoology, Louisiana State University, Baton Rouge, Louisiana