Reconstructing geographical parthenogenesis: effects of niche differentiation and reproductive mode on Holocene range expansion of an alpine plant

Asexual taxa often have larger ranges than their sexual progenitors, particularly in areas affected by Pleistocene glaciations. The reasons given for this ‘geographical parthenogenesis’ are contentious, with expansion of the ecological niche or colonisation advantages of uniparental reproduction assumed most important in case of plants. Here, we parameterized a spread model for the alpine buttercup Ranunculus kuepferi and reconstructed the joint Holocene range expansion of its sexual and apomictic cytotype across the European Alps under different simulation settings. We found that, rather than niche broadening or a higher migration rate, a shift of the apomict's niche towards colder conditions per se was crucial as it facilitated overcoming of topographical barriers, a factor likely relevant for many alpine apomicts. More generally, our simulations suggest potentially strong interacting effects of niche differentiation and reproductive modes on range formation of related sexual and asexual taxa arising from their differential sensitivity to minority cytotype disadvantage.     

Antibiotic‐induced effects on scaling relationships and on plant element contents in herbs and grasses

Plant performance is correlated with element concentrations in plant tissue, which may be impacted by adverse chemical soil conditions. Antibiotics of veterinary origin can adversely affect plant performance. They are released to agricultural fields via grazing animals or manure, taken up by plants and may be stored, transformed or sequestered by plant metabolic processes. We studied the potential effects of three antibiotics (penicillin, sulfadiazine, and tetracycline) on plant element contents (macro‐ and microelements). Plant species included two herb species (Brassica napus and Capsella bursa‐pastoris) and two grass species (Triticum aestivum and Apera spica‐venti), representing two crop species and two noncrop species commonly found in field margins, respectively. Antibiotic concentrations were chosen as to reflect in vivo situations, that is, relatively low concentrations similar to those detected in soils. In a greenhouse experiment, plants were raised in soil spiked with antibiotics. After harvest, macro‐ and microelements in plant leaves, stems, and roots were determined (mg/g). Results indicate that antibiotics can affect element contents in plants. Penicillin exerted the greatest effect both on element contents and on scaling relationships of elements between plant organs. Roots responded strongest to antibiotics compared to stems and leaves. We conclude that antibiotics in the soil, even in low concentrations, lead to low‐element homeostasis, altering the scaling relationships between roots and other plant organs, which may affect metabolic processes and ultimately the performance of a plant.     

Carboxyl-terminal processing of the cytoplasmic NAD-reducing hydrogenase of Alcaligenes eutrophus requires the hoxW gene product.

Two open reading frames (ORFs) were identified immediately downstream of the four structural genes for the soluble hydrogenase (SH) of Alcaligenes eutrophus H16. While a mutation in ORF2 had no obvious effect on hydrogen metabolism, an in-frame deletion in ORF1, subsequently designated hoxW, led to a complete loss of SH activity and hence a significant retardation of autotrophic growth on hydrogen. Hydrogen oxidation in the hoxW mutant was catalyzed by the second hydrogenase, a membrane-bound enzyme. Assembly of the four subunits of the SH was blocked in mutant cells, and HoxH, the hydrogen-activating subunit, accumulated as a precursor which was still capable of binding nickel. Protein sequencing revealed that HoxH isolated from the wild type terminates at His-464, whereas the C-terminal amino acid sequence of HoxH from the hoxW mutant is colinear with the deduced sequence. Processing of the HoxH precursor was restored in vitro by a cell extract containing HoxW. These results indicate that HoxW is a highly specific carboxyl-terminal protease which releases a 24-amino-acid peptide from HoxH prior to progression of subunit assembly.     

Long-term persistence in a changing climate: DNA analysis suggests very old ages of clones of alpine Carex curvula

Carex curvula is a very slow-growing rhizomatous sedge that forms extensive stands in the European an alpine belt. The recruitment of sexual progeny is extremely rare and propagation occurs predominantly through clonal growth. The randomly amplified polymorphic DNA (RAPD) technique was used to analyse clonal structure in a small patch (2.0x0.4 m sampling transect plus some additional samples) of a high-alpine population of the species. Amplification of the DNA of 116 tiller samples from the patch with eight ten-base primers yielded a total of 95 bands, of which 73 were polymorphic. Based on the RAPD amplification profiles a total of 15 multilocus genotypes (putative clones) were identified. Due to the high number of polymorphic loci the number of genetic markers delineating individual clones was high (range: 16–39 markers) which suggests that our estimates of clonal diversity are precise. More than half of the sampled tillers were identified as belonging to a single clone which formed a relatively homogeneous disc intermingling with other clones only at its margin. Based on the maximum diameter of this large clone of more than 7000 tillers and estimates of annual expansion growth of rhizomes (0.4 mm year^-1), the age of the clone was calculated to be around 2000 years. This demonstrates that clones of C. curvula may persist on a single spot over long periods with quite diverse alpine climates ranging from rather mild periods in the Middle Ages to cool periods during the so called little ice age in the last century. Our results suggest caution with plant migration scenarios based on shifting isotherms where late-successional clonal species, which dominate the alpine vegetation all over the world, are concerned.     

Diurnal modulation of phosphoenolpyruvate carboxylation in pea leaves and roots as related to tissue malate concentrations and to the nitrogen source

Phosphoenolpyruvate (PEP) carboxylation was measured as dark ¹⁴CO₂ fixation in leaves and roots (in vivo) or as PEP carboxylase (PEPCase) activity in desalted leaf and roof extracts (in vitro) from Pisum sativum L. cv. Kleine Rheinländerin. Its relation to the malate content and to the nitrogen source (nitrate or ammonium) was investigated. In tissue from nitrate-grown plants, PEP carboxylation varied diurnally, showing an increase upon illumination and a decrease upon darkening. Diurnal variations in roots were much lower than in leaves. Fixation rates in leaves remained constantly low in continuous darkness or high in continuous light. Dark CO₂ fixation of leaf slices also decreased when leaves were preilluminated for 1 h in CO₂-free air, suggesting that the modulation of dark CO2 fixation was related to assimilate availability in leaves and roots. Phosphoenolpyruvate carboxylase activity was also measured in vitro. However, no difference in maximum enzyme activity was found in extracts from illuminated or darkened leaves, and the response to substrate and effectors (PEP, malate, glucose-6-phosphate, pH) was also identical. The serine/threonine protein kinase inhibitors K252b, H7 and staurosporine, and the protein phosphatase 2A inhibitors okadaic acid and cantharidin, fed through the leaf petiole, did not have the effects on dark CO₂ fixation predicted by a regulatory system in which PEPCase is modulated via reversible protein phosphorylation. Therefore, it is suggested that the diurnal modulation of PEP carboxylation in vivo in leaves and roots of pea is not caused by protein phosphorylation, but rather by direct allosteric effects. Upon transfer of plants to ammonium-N or to an N-free nutrient solution, mean daily malate levels in leaves decreased drastically within 4–5 d. At that time, the diurnal oscillations of PEP carboxylation in vivo disappeared and rates remained at the high light-level. The coincidence of the two events suggests that PEPCase was de-regulated because malate levels became very low. The drastic decrease of leaf malate contents upon transfer of plants from nitrate to ammonium nutrition was apparently not caused by increased amino acid or protein synthesis, but probably by higher decarboxylation rates.Abbreviations CAM crassulacean acid metabolism - PEP Phosphoenolpyruvate - PEPCase phosphoenolpyruvate carboxylase - PP protein phosphatase - PK protein kinase This work was supported by the Deutsche Forschungsgemeinschaft. B. Baur was a recipient of a doctoral grant, and L. Leport recipient of a post-doctoral grant of the DFG. The skilled technical assistance of Eva Wirth and Maria Lesch is gratefully acknowledged.     

The monofunctionalized 1,4,7-triazacyclononane derivatives 1,4,7-triazacyclononane-N-acetate (L) and N-(2-hydroxybenzyl-1,4,7-triazacyclononane (HL) and their complexes with vanadium(IV)/(V). Localized and delocalized electronic structures in compounds containing the mixed valent [OV---O---VO] core

The synthesis of the tetradentate pendant arm macrocycles 1,4,7-triazacyclononane-N-acetate (L¹) and N-(2-hydroxybenzyl)-1,4,7-triazacyclononane (HL²) and their coordination chemistry with vanadium(IV) and (V) are reported. The following mononuclear species have been prepared and characterized by UV-Vis, IR spectroscopy: [L¹V^IVO(NCS)] (1), [L¹VO₂]·H₂O (2), [L²VO(NCS)] (3), [L²VO(NCS)]Cl (4), and [L²VO₂] (5). In addition, the dinuclear, mixed valent complexes [L₂¹V₂O₃]Br (6), [L₂²V₂O₃](ClO₄)·0.5acetone (7), and the homovalent complex [L₂²V₂O₃](ClO₄)₂ (8) have been synthesized. Complexes 2, 3, 6 and 7 have been characterized by single crystal X-ray crystallography. Crystal data: 2, space group P2₁c,a=9.944(4),b=6.701(3),c=18.207(8)Å, β=102.88(3)°, V=1182.7 ų, Z=4, D_calc=1.51 g cm⁻³, R=0.049 based on 4760 reflections; 3, space group Pbca, A=11.003(6), b=14.295(7), C=20.21(1) Å, V=3178.8 ų, Z=8, D_calc=1,50 g cm⁻³, R=0.057 based on 1049 reflections; 6, space Pbcn, a=12.922(3), B=13.852(3), C=12.739(3) Å, V=2280.3 ų, Z=4, D_calc=1,75 g cm⁻³, R=0.047 based on 1172 reflections; 7, space group C2/c, A=23.553(9), B=13.497(5), C=20.951(8) Å, β=90.03(3)°, V=6660.2 ų, Z=8, D_calc=1.49 g cm⁻³, R=0.053 based on 3698 reflections. Complexes 6 and 7 are mixed valent V(IV)/(V) complexes containing the [OV---O---VO]³⁺ core. In the solid state 6 belongs to class III (delocalized) and 7 to class I (localized) according to the Robin and Day classification of mixed valent compounds. A rationale for these differing electronic structures is given.     

A 23 kDa membrane glycoprotein bearing NeuNAc{alpha}2-3Gal{beta}1-3GalNAc O-linked carbohydrate chains acts as a receptor for Streptococcus sanguis OMZ 9 on human buccal epithelial cells

Streptococcus sanguis colonizes several human oral surfaces,including both hard and soft tissues. Large salivary mucin likeglycoproteins bearing sialic acid residues are known to bindvarious S.sanguis strains. However, the molecular basis forthe adhesion of S.sanguis to human buccal epithelial cells (HBEC)has not been established. The present study shows that S.sanguisOMZ 9 binds to exfoliated HBEC in a sialic acid-sensitive manner.The desialylation of such cells invariably abolhhes adhesionof S.sanguis OMZ 9 to the cell surface. A soluble glycopeptidebearing short sialylated O-linked carbohydrate chains behavesas a potent inhibitor of the attachment of S.sanguis OMZ 9 toexfoliated HBEC. The resialylation of desialylated HBEC withCMP-sialic acid and Galß1,3GalNAc     

Exposure to polychlorinated biphenyls causes endothelial cell dysfunction

Environmental chemicals, such as polychlorinated biphenyls (PCBs), may be atherogenic by disrupting normal functions of the vascular endothelium. To investigate this hypothesis, porcine pulmonary artery-derived endothelial cells were exposed to 3,3′,4,4′-tetrachlorobiphenyl (PCB 77), 2,3,4,4′,5-pentachlorobiphenyl (PCB 114), or 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153) for up to 24 hours. These PCBs were selected for their varying binding avidities with the aryl hydrocarbon (Ah) receptor and differences in their induction of cytochrome P450. PCB 77 and PCB 114 significantly disrupted, in a dose-dependent manner, endothelial barrier function by allowing an increase in albumin transfer across endothelial monolayers. These PCBs also contributed markedly to cellular oxidative stress, as measured by 2,7-dichlorofluorescin (DCF) fluorescence and lipid hydroperoxides, and caused a significant increase in intracellular calcium ([Ca²⁺]_i) levels. Enhanced oxidative stress and [Ca²⁺]_i in PCB 77- and PCB 114-treated cells were accompanied by increased activity and content of cytochrome P450 1A and by a decrease in the vitamin E content in the culture medium. In contrast to the effects of PCB 77 and PCB 114, cell exposure to PCB 153 had no effect on cellular oxidation, [Ca²⁺]_i, or endothelial barrier function. These results suggest that certain PCBs may play a role in the development of atherosclerosis by causing endothelial cell dysfunction and a decrease in the barrier function of the vascular endothelium. It is possible that interaction of PCBs with the Ah receptor and activation of the cytochrome P450 1A subfamily are involved in this pathology. © 1995 John Wiley & Sons, Inc.     

Effects of ionizing radiation on cell cycle progression

Irradiation of normal eukaryotic cells results in delayed progression through the G1, S, and G2 phases of the cell cycle. The G1 arrest is regulated by the p53 tumor suppressor gene product. Irradiation results in increased expression of p53, which in turn induces a 21 kDa protein, WAF 1/Cip 1, that inhibits cyclin CDK kinases. S-phase delay is observed after relatively high doses of radiation. This delay has both radiosensitive and radioresistant components, corresponding to inhibition of DNA replicon initiation and DNA chain elongation, respectively. The mechanism for this delay is as yet undefined, but the extent of the delay appears to be under genetic control and is sensitive to the kinase inhibitor staurosporine. A delay in G2 has been demonstrated in virtually all eukaryotic cells examined in response to irradiation. Our studies have focused on the mechanisms responsible for this delay. Cyclin B1 and p34^cdc2 are cell cycle control proteins that together form a kinase complex required for passage through G2 and mitosis [22]. Control of radiation-induced G2 delay is likely therefore to involve modulation of cyclin B1/p34^cdc2 activity. We have shown in HeLa cells that cyclin B1 expression is decreased in a dose-dependent manner following irradiation. This decrease is controlled at both the level of mRNA and protein accumulation. We have also shown that radiation-sensitive rat embryo fibroblast lines (REF) immortalized with v- or c-myc display a minimal G2 delay when compared to radiation resistant cells transformed with v-myc + H-ras. These REF lines respond to irradiation with a decrease in cyclin B mRNA, which parallels the extent of their respective G2 delays. The duration of the G2 delay in radiation-resistant REF can be shortened by treatment with low doses of the kinase inhibitor staurosporine. We have also been able to markedly reduce the radiation-induced G2 delay in HeLa cells using either staurosporine or caffeine. Attenuation of the G2 delay is accompanied by reversal of the radiation-induced inhibition of cyclin B mRNA accumulation. The results of these studies are consistent with the hypothesis that reduced expression of cyclin B in response to radiation is in part responsible for the G2 delay. The duration of the G2 delay may also be influenced by the activation state of the cyclin B/p34_cdc2 complex.Invited paper presented at the International Symposium on Heavy Ion Research: Space, Radiation Protection and Therapy, Sophia-Antipolis, France, 21–24 March 1994