Facultative parthenogenesis and sex-ratio evolution

Summary Phenotypic models of selection are used to determine the effect of facultative parthenogenesis on the production of males in a spatially variable environment when (i) sex determination is under strict genetic control, and (ii) when sex may be environmentally determined. The results show that when sex is under strict genetic control and there is some chance of maturing in isolation, selection favors a female-biased sex ratio. When sex can be environmentally induced by cues which indicate high density, selection favors a mixture of genetic and environmental control, such that half the individuals always become female and the other half become females when isolated and become males when not isolated.     

Growth and senescence in plant communities exposed to elevated CO2 concentrations on an estuarine marsh

Summary Three high marsh communities on the Chesapeake Bay were exposed to a doubling in ambient CO₂ concentration for one growing season. Open-top chambers were used to raise CO₂ concentrations ca. 340 ppm above ambient over monospecific communities of Scirpus olneyi (C₃) and Spartina patens (C₄), and a mixed community of S. olneyi, S. patens, and Distichlis spicata (C₄). Plant growth and senescence were monitored by serial, nondestructive censuses. Elevated CO₂ resulted in increased shoot densities and delayed sensecence in the C₃ species. This resulted in an increase in primary productivity in S. olneyi growing in both the pure and mixed communities. There was no effect of CO₂ on growth in the C₄ species. These results demonstrate that elevated atmospheric CO₂ can cause increased aboveground production in a mature, unmanaged ecosystem.     

Temporal mechanisms influencing gender expression and pollen flow within a self-incompatible perennial,Amianthium muscaetoxicum (Liliaceae)

Summary Temporal mechanisms that influence the synchrony of gender expression and the patterns of withinplant pollen flow were examined in Amianthium muscatoxicum. In this species self-incompatible pollinations can clog stigmas, interfere with the growth of outcrossed pollen tubes, and reduce fecundity. The majority of flowers have partial dichogamy: a two-day period of pollen dehiscence and a four-day period of pollen viability are nested in a six-day period of pistil viability. An indeterminate flowering sequence among flowers on the same plant and partial dichogamy within flowers help reduce pollen flow within the whole plant. The combined effects at both of these levels should reduce pollen wastage and lower the incidence of stigma clogging by incompatible self pollen.     

Effect of Inhibition of Glycosylation on the Appearance of a 60 kD Membrane Glycopolypeptide in Endomembrane Fractions of Soybean Root

Endomembrane (endoplasmic reticulum, Golgi apparatus, plasma membrane) proteins of soybean (Glycine max) root cells are highly glycosylated. We investigated whether N-linked oligosaccharide moieties are essential for the correct intracellular transport of plant endomembrane glycoproteins. Excised roots were incubated with tunicamycin, to block cotranslational glycosylation of proteins, and dual labeled with [³H]glucosamine and [³⁵S] (methionine, cysteine). In the presence of tunicamycin, the incorporation of glucosamine into membrane proteins was inhibited by 60 to 90% while amino acid incorporation was only slightly affected. Autoradiograms of two-dimensionally separated polypeptides from each endomembrane fraction revealed the presence of at least one new polypeptide in tunicamycin-treated tissue. The new polypeptide was of the same isoelectric point but lower molecular weight than a preexisting polypeptide. The new polypeptide was unreactive to concanavalin A, as opposed to the preexisting polypeptide, suggesting the absence of the glycan portion. Trifluoromethanesulfonic acid and N-glycanase were used to cleave the carbohydrate from the preexisting concanavalin A binding polypeptide. In each case a deglycosylated polypeptide of the same isoelectric point and molecular weight as the new polypeptide from tunicamycin-treated tissue resulted. Since the absence of carbohydrate from the new endomembrane polypeptide did not prevent its appearance on autoradiograms of Golgi and plasma membrane, intracellular transport and intercalation of newly synthesized glycoproteins into plant cell membranes may not require the presence of polysaccharide moieties.     

A specific rearrangement of mitochondrial DNA induced by tissue culture

Summary The induction, growth and regeneration of sugar beet callus to whole plants were all found to be highly genotype-specific. Regenerants of one line (of sterile cytoplasm) were obtained and a study of the chloroplast and mitochondrial DNA in these somaclones was undertaken by gel electrophoresis and cosmid hybridization. In one somaclone a rearrangement in the mitochondrial genome was observed; the novel arrangement of this part of the genome was identical to the corresponding area of the genome of the normal cytoplasm though it was otherwise of sterile type. This suggests that mitochondrial DNA may have a propensity to undergo certain types of rearrangement.     

A selective differential medium for the isolation of Listeria monocytogenes

A new medium has been developed for the isolation of Listeria monocytogenes from clinical specimens with a mixed flora. Almost complete inhibition of unwanted organisms was achieved and recognition of colonies of Listeria spp. was usually possible after 24 h using the aesculin-ferric ammonium citrate indicator system. Compared to McBride agar the new medium was more inhibitory to representative contaminating species in pure culture and more successful in isolating small numbers of L. monocytogenes from artificially seeded clinical specimens.     

Mn2+ reduces Yz + in manganese-depleted Photosystem II preparations

Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn²⁺. Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Y_z ⁺, the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Y_z ⁺ reduction by benzidine was a linear function of benzidine concentration. The rate of Y_z ⁺ reduction by Mn²⁺ at pH 6 increased linearly at low Mn²⁺ concentrations and reached a maximum at the Mn²⁺ concentrations equal to several times the reaction center concentration. The rate was inhibited by K⁺, Ca²⁺ and Mg²⁺. These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Y_z ⁺ reduction at pH 7.5 was biphasic with a fast 400 s phase that suggests binding of Mn²⁺ near Y_z ⁺ at a site that may be one of the native manganese binding sites.Abbreviations PS II Photosystem II - Y_D tyrosine residue in Photosystem II that gives rise to the stable Signal II EPR spectrum - Y_z tyrosine residue in Photosystem II that mediates electron transfer between the reaction center chlorophyll and the site of water oxidation - ESR electron spin resonance - DPC diphenylcarbazide - DCIP dichlorophenolindophenol     

Molecular Analysis of Recombination Events in Drosophila

The locations of crossover junctions and gene conversion tracts, isolated in the rosy gene of Drosophila melanogaster, were determined using DNA sequencing and denaturing gradient gel electrophoresis. Frequent DNA sequence polymorphisms between the parental genes served as unselected genetic markers. All conversion tracts were continuous, and half of the reciprocal crossover events had conversion tracts at the crossover junction. These experiments have also identified the sequence polymorphisms responsible for altered gene expression in two naturally occurring rosy variants.     

The primary role of the P1 residue (ser359) of alpha-1-proteinase inhibitor

The replacement of ser359 with ala359 at the P1 position in human alpha-1-proteinase inhibitor results in the production of a variant protein containing 15% of the inhibitory activity of the normal inhibitor. Separation of active from inactive inhibitor on anhydrochymotrypsin-sepharose yields a form which has a second order association rate with neutrophil elastase which is approximately one half that for the native protein. These data indicate that the P1 residue is not of primary importance during the interaction of proteinases with alpha-1-proteinase inhibitor. Since substitution of alanine for serine causes the formation, primarily, of inactive inhibitor the major function of ser359 probably involves proper folding to give a functionally active inhibitory conformation.     

12S,19- and 12S,20-dihydroxyeicosanoids: novel 12S-hydroxy-5,8-cis-10-trans-14-cis-eicosatetraenoic acid metabolites formed by hydroxylation and reduction in murine lymphocytes

Murine spleen cells and purified B lymphocytes oxidized arachidonic acid via the lipoxygenase pathway. The major metabolite of both the whole spleen and enriched B lymphocytes was 12S-hydroxy-5,8-cis-10-trans-14-cis-eicosatetraenoic acid. A novel metabolite was observed that did not have an absorbance from 210 to 400 nm, indicating the absence of a conjugated double bond system. The new metabolite was converted to the methyl ester, reduced by platinum oxide, derivatized to the trimethylsilyl ether, and analyzed by gas chromatography-mass spectrometry. A major and a minor component were observed in the analysis of the new compound. The major component had major diagnostic ions indicating the presence of hydroxyl groups at C-12 and C-19. The minor component had major diagnostic ions indicating the presence of hydroxyl groups at C-12 and C-20. The new metabolites are characterized as a mixture of 12S,19- and 12S,20-dihydroxyeicosanoids presumably formed by hydroxylation and reduction of one or more double bonds of 12S-hydroxy-5,8-cis-10-trans-14-cis-eicosatetraenoic acid. These metabolites were formed predominantly with whole spleen lymphocytes but could be detected at longer incubation times or by using 12S-hydroxy-5,8-cis-10-trans-14-cis-eicosatetraenoic acid as the starting substrate with highly enriched B lymphocytes.