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  • 1
    Electronic Resource
    Electronic Resource
    Progesterone Can Block the Preovulatory Gonadotropin-Releasing Hormone/Luteinising Hormone Surge in the Ewe by a Direct Inhibitory Action on Oestradiol-Responsive Cells within the Hypothalamus (2005)
    Oxford, UK : Blackwell Science Ltd
    Journal of neuroendocrinology 17 (2005), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Elevated oestradiol concentrations during the follicular phase stimulate a surge in gonadotropin-releasing hormone (GnRH) and luteinising hormone (LH) concentrations, which leads to ovulation. Progesterone can block the oestradiol-induced GnRH/LH surge, but the mechanism that is involved is unclear. We examined the effect of progesterone on oestradiol-induced activation of cells within the ovine hypothalamus/preoptic area (POA) to determine: (i) in which regions progesterone acts to block the GnRH/LH surge and (ii) whether progesterone directly or indirectly prevents activation of oestradiol-responsive cells. Cellular activation was assessed by measuring the number of cells that expressed Fos (an immediate early gene). Exposure to increased oestradiol concentrations in the absence of progesterone (which normally stimulates a LH surge) did not cause any region-specific changes in hypothalamic Fos expression during the activation stage of the LH surge-induction process (Experiment 1). The same treatment significantly increased cellular activation within the POA, lateral septum (LS), and arcuate nucleus at the time of surge onset (Experiment 2). Concurrent exposure to increased oestradiol and progesterone concentrations during the activation stage of the surge-induction process (which normally blocks the LH surge) was associated with significantly reduced cellular activation within the ventromedial hypothalamus and anterior hypothalamic area, relative to the positive controls (oestradiol increment alone) and arcuate nucleus relative to the negative controls (no increment in oestradiol) during the activation stage (Experiment 1). At the time of surge onset (Experiment 2), exposure to progesterone during the activation period prevented the oestradiol-induced increase in cellular activation that occurred in the POA, LS and arcuate nucleus of the positive controls. These results demonstrated that oestradiol and progesterone induced differential region- and time-specific effects on cellular activation within the regions of the ovine brain that generate the preovulatory GnRH/LH surge. Moreover, the lack of cellular activation within the POA, LS and arcuate nucleus at the time of surge onset in animals exposed to progesterone during the activation stage is consistent with the hypothesis that progesterone can block the preovulatory surge by direct inhibition of oestradiol-induced cellular activation in these areas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.2005.01287.x
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  • 2
    Electronic Resource
    Electronic Resource
    Mycorrhizal colonization and drought stress affect Δ13C in 〈CO2-labeled lettuce plants (2000)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 109 (2000), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We studied the role of different arbuscular-mycorrhizal (AM) fungi on lettuce (Lactuca sativa L.) plant carbon metabolism under drought stress. Plants were grown in pots maintained at two levels of soil moisture and labeled during photosynthesis with 〈displayedItem type="mathematics" xml:id="di-fml-2" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00319317:PPL100307:PPL_100307_mu2"/〉CO2. P-fertilized plants were used as a non-mycorrhizal control. Well-watered mycorrhizal plants showed similar growth to that of P-fertilized plants. The level of mycorrhizal root infection was not significantly affected by fungal species or by water treatment. In contrast, important differences in Δ13C between P-fertilized and AM plants were found in shoot and root tissues as a consequence of both water limitation and fungal presence. Δ13C in shoots and roots increased in non-mycorrhizal treatment as compared with the well-watered plants, whereas this parameter decreased significantly in mycorrhizal plants. Photosynthetic activity was increased in AM plants in well-watered and droughted plants. G. deserticola was the most beneficial endophyte for water use efficiency in both water treatments. Transpiration rate was not affected by any of the treatments. On the basis of total 〈displayedItem type="mathematics" xml:id="di-fml-3" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00319317:PPL100307:PPL_100307_mu3"/〉 C in plant tissues, in AM plants the newly fixed C seemed to be preferentially utilized for fungal activity rather than being stored in roots.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2000.100307.x
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  • 3
    Electronic Resource
    Electronic Resource
    Hyphal contribution to water uptake in mycorrhizal plants as affected by the fungal species and water status (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 95 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Vesicular-arbuscular mycorrhizae may increase resistance of plants to drought by a number of mechanisms, such as increased root hydraulic conductivity, stomatal regulation, hyphal water uptake and osmotic adjustment. However, a substantial contribution of vesicular-arbuscular mycorrhizal (VAM) hyphae to water uptake has not been demonstrated unequivocally. The objective of this investigation was to examine the contribution of hyphae from two VAM fungi to water uptake and transport by the host plant. Lettuce (Lactuca sativa L.) plants were grown in a container divided by a screen into two compartments. One was occupied by roots, the other only by VAM hyphae, which the screen permitted to pass. Roots were colonized by the VAM fungi Glomus deserticola or Glomus fasciculatum, or were left uninoculated but P-supplemented. Water was supplied to the hyphal compartment at a distance of 10 cm from the screen (root). CO2 exchange rate, water-use efficiency, transpiration, stomatal conductance and photosynthetic phosphorus-use efficiency of VAM or P-amended control plants were evaluated at three levels of water application in the hyphal compartment. Results indicate that much of the water was taken up by the hyphae in VAM plants. VAM plants, which had access to the hyphal compartment, had higher water and nutrient contents. G. deserticola functioned efficiently under water limitation and mycelium from G. fasciculatum-colonized plants was very sensitive to water in the medium. This discrepancy in VAM behaviour reflects the various abilities of each fungus according to soil water levels. Different abilities of specific mycelia were also expressed in terms of nutritional and leaf gas-exchange parameters. G. fasciculatum caused a significant increase in net photosynthesis and rate of water use efficiency compared to G. deserticola and P-fertilized plants. In contrast, the G. deserticola treatment was the most efficient affecting N, P and K nutrition, leaf conductance and transpiration. Since no differences in the intra- and extra-radical hyphal extension of the two endophytes were found, the results demonstrate that mycorrhizal hyphae can take up water and that there are considerable variations in both the behaviour of these two VAM fungi and in the mechanisms involved in their effects on plant water relations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb00865.x
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  • 4
    Electronic Resource
    Electronic Resource
    Alleviation of salt stress by arbuscular-mycorrhizal Glomus species in Lactuca sativa plants (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 98 (1996), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Improved salt tolerance of mycorrhizal plants is commonly attributed to their better mineral nutrition, particularly phosphorus. However, the effect of arbuscular-mycorrhizal (AM) fungi on salt tolerance may not be limited to this mechanism. We investigated the possibility that non-nutritional effects of AM fungi, based on proline accumulation or increased photosynthesis and related parameters, can influence the tolerance of lettuce (Lactuca sativa L.) to salinity. Three levels of salt (3, 4 and 5 g NaCl kg-1 dry soil) were applied and plants were maintained under these conditions for 7 weeks. The salt-treated AM plants produced greater root and shoot dry weights than unfertilized or P-fertilized non-AM controls. With increasing salinity, both shoot and root dry weights were reduced, but this decrease was greater in uninoculated plants. In particular, shoot dry weight was not reduced in G. fasciculatum-colonized plants as a consequence of salt, whereas in uninoculated plants it was reduced by about 35% at the highest salt level. Proline accumulation was considerably lower for P-amended non-AM and for AM plants except for G. mosseae-colonized plants than was the case for unamended plants. Transpiration, carbon dioxide exchange rate (CER), stomatal conductance and water use efficiency (WUE) were higher in mycorrhizal plants. At 5 g NaCl kg-1, both photosynthesis and WUE increased by more than 100% in mycorrhizal treatment relative to uninoculated plants. The contents of phosphorus of P-fertilized non-AM plants was similar to or higher than those of G. mosseae- and G. fasciculatum-colonized plants. Plants colonized by G. deserticola had the highest P-content regardless of salt level. Hence, the effect of G. mosseae and G. fasciculatum on salt tolerance in this experiment could not be attributed to a difference in the P content. The mechanisms by which these two fungi alleviated salt stress appeared to be based on physiological processes (increased CER, transpiration, stomatal conductance and WUE) rather than on nutrient uptake (N or P).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1996.tb06683.x
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  • 5
    Electronic Resource
    Electronic Resource
    Genes involved in resistance to powdery mildew in barley differentially modulate root colonization by the mycorrhizal fungus Glomus mosseae (1999)
    Springer
    Mycorrhiza 9 (1999), S. 237-240 
    Details
    ISSN: 1432-1890
    Keywords: Key words Barley ; Glomus mosseae ; Powdery mildew ; Non-race-specific resistance ; Race-specific resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Arbuscular mycorrhizal fungi (AMF) and Erysiphe graminis are obligate biotrophic fungi with different outcomes in their interaction with plants, different targeted host tissues, but similar patterns of development and infection processes. These similarities raise the question of whether the two types of biotrophic fungal infections have common features in their regulation. To investigate this question, we compared a number of Ror and Rar barley mutants susceptible to E.graminis f. sp. hordei, as well as their resistant progenitors, for susceptibility to infection by the AMF Glomus mosseae. The two powdery mildew-resistant lines BC Ingrid and Sultan presented a similar reduction in G. mosseae development within roots when compared to the wildtype cultivar Ingrid, indicating a systemic effect of the altered genes in the plant. Ror and Rar mutants, in which susceptibility to powdery mildew is restored, showed increased resistance to AM fungal development in their roots when compared to their progenitors, which suggests that corresponding mutations must have affected genes which differentially modulate symbiotic and pathogenic biotrophic plant-fungus interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005720050273
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  • 6
    Electronic Resource
    Electronic Resource
    Symbiotic efficiency and infectivity of an autochthonous arbuscular mycorrhizal Glomus sp. from saline soils and Glomus deserticola under salinity (2000)
    Springer
    Mycorrhiza 10 (2000), S. 137-143 
    Details
    ISSN: 1432-1890
    Keywords: Keywords Arbuscular-mycorrhiza ; Infectivity ; Fungal isolate ; Salt stress ; Symbiotic efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The purpose of this study was to compare the effect of salinity on the symbiotic efficiencies and mycelial infectivity of two arbuscular mycorrhizal fungi (AMF), one isolated from saline soils (Glomus sp.) and the other (Glomus deserticola) from nonsaline soils (belonging to the Estación Experimental del Zaidín collection). Lettuce plants inoculated with either of these two fungi or maintained as uninoculated controls were grown in soil with three salt concentrations (0.25, 0.50 or 0.75 g NaCl kg–1 dry soil). Both AMF protected host plants against salinity. However, when the results of shoot dry weight and nutrient contents were expressed relative to the total length of mycorrhiza formed, it was found that both AMF differed in their symbiotic efficiencies. These differences were more evident at the two highest salt levels. Glomus sp.-colonized plants grew less and accumulated less N and P, whereas they formed a higher amount of mycorrhiza. The mechanism by which Glomus sp. protected plants from the detrimental effects of salt was based on the stimulation of root development, while the effects of G. deserticola were based on improved plant nutrition. The increase in salinity of soil decreased the hyphal growth and/or viability of Glomus sp. to a higher extent than those of G. deserticola since the mycelial network generated by G. deserticola was more infective than that of Glomus sp.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005720000075
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  • 7
    Electronic Resource
    Electronic Resource
    Calorimetric study of the proximity effect in aliphatic diesters (1985)
    Springer
    Journal of thermal analysis and calorimetry 30 (1985), S. 1393-1396 
    Details
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Bei Atmosphärendruck und 303,15 K gemessene molare Überschußenthalpien (H E werden für binäre Gemische von 1-Chlorhexan mit Diäthyloxalat, Diäthylmalonat, Diäthylsuccinat, Diäthylglutarat, Diäthyladipat, Diäthylpimelat bzw. Diäthylsebacat angegeben. Diese experimentellen Ergebnisse werden zusammen mit den früher für Gemische von aliphatischen Diestern und n-Hexan erhaltenen Resultaten als molekulare Oberflächenwechselwirkungen zwischen aliphatischen, chlorierten und Carboxylatgruppen interpretiert. Ein Vergleich der Enthalpieaustauschparameter läßt eine Verminderung der intermolekularen Wechselwirkungen mit abnehmendem intramolekularem Abstand zwischen den COO-Gruppen erkennen.
    Abstract: Резюме Приведены избыточны е молярные энтальпии (H E ) при атмосферном дав лении и температуре 303,15 K для дво йных смесей 1-хлоргекс ана с диэтиловыми эфирами щавелевой, малоновой, сукциново й, глутаровой, адипино вой, пимелиновой и себаци новой кислот. Получен ные экспериментальные р езультаты, наряду с ра нее измеренными для смес ей алифатический диэфир + н-гексан, интер претированы на основ е молекулярных поверх ностных взаимодейст вий между алифатической, хлорзамещенной и сло жноэфирной группами. Сопоставле ние энтальпийных взаимообменных пара метров показывает ум еньшение межмолекулярных вза имодействий с одновременным умень шением внутримолеку лярных COO-COO взаимодействий.
    Notes: Abstract Excess molar enthalpies,H E , at atmospheric pressure and 303.15 K are reported for binary mixtures of 1-chlorohexane with diethyl oxalate, diethyl malonate, diethyl succinate, diethyl glutarate, diethyl adipate, diethyl pimelate and diethyl sebacate. These experimental results, together with those obtained previously on the excess enthalpies of aliphatic diester+n-hexane mixtures, are interpreted in terms of molecular surface interactions between aliphatic, chlorinated and carboxylate groups. Comparison of the enthalpy interchange parameters reveals a decrease of the intermolecular interactions with decreasing intramolecular COO-COO distance in the diester molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01914312
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