Sirvi Kuupäev , alustades "2010-01-14" järgi

Filtreeri tulemusi aasta või kuu järgi

Nüüd näidatakse 1 - 3 3

Ain Kallis: pühvliaasta tõi ilma osas kõiksugu pulli
(Maaleht, 2010-01-14) Kallis, A.
Ligand binding to 5-HT1A receptors and its regulation by Mg2+ and Mn2+
(Tartu University Press, 2010-01-14T08:04:14Z) Parkel, Sven
In the first part of this thesis the binding of 5-HT1A receptor specific antagonist [3H]WAY100635 to rat brain membranes was characterized. It was found, that the binding on lower concentrations was considerably slow, and a notable amount of receptors will be inactivated before thermodynamic equilibrium can be reached, yet on higher concentrations rapid increase in reaction rate indicative of cooperative binding was detected. This means that [3H]WAY100635 is an excellent tool for determining receptor number in a given sample, but not a very good ligand in equilibrium binding studies. In the second part of this thesis the influence of Mn2+ in comparison to Mg2+ to signal transduction via 5-HT1A receptors was measured. It was shown that Mn2+ can stabilize greater number of agonist high-affinity binding sites, while the size of this effect depended on the used brain region (different in hippocampal and cortical membranes) and also on the GTPγS concentration. Since GTPγS activates G-proteins, sensitivity to its concentration refers to the involvement of G-proteins in the enhancing regulation by Mn2+. Sf9 cell lines were created for comparison expressing only 5-HT1A receptor or the receptor with Gi or Gs protein. Agonist high affinity binding was achieved only in cell line expressing the receptor with Gi protein, and the sensitivity of this cell line to Mn2+ was similar to cortical preparations but different from hippocampal membranes. To clarify the role of G-proteins on this regulation, influence of Mn2+ compared to Mg2+ to the affinity of guanosine nucleotides (GDP and GTPγS) binding to G-proteins was measured. Mn2+ lowered the affinity of both GDP and GTPγS compared to Mg2+, and the size of the effect was again dependent on used brain region, showing that there are differences in the composition of signaling complexes that are formed with 5-HT1A receptor in different brain regions. Additionally there seem to be differences in the sensitivity of these complexes to Mn2+-ions.
Mycorrhizal fungi of native and introduced trees in the Seychelles Islands
(2010-01-14T14:12:15Z) Suvi, Triin
Mycorrhiza is a mutualistic relationship between plants and fungi. Fungi provide mineral nutrients (N, P) to the host plant that, in return, transfers carbohydrates fixed via photosynthesis to the fungus. Mycorrhiza is divided into different types based on morphology/anatomy of the colonized root. In case of ectomycorrhiza (EcM) fungus forms a fungal sheath around the root tip and Hartig net between the cortical cells. EcM is most common in temperate regions, but can also be found in tropics. Study was carried out in the Seychelles archipelago that consists of more than one hundred granitic, coral and sand islands that are situated in Indian Ocean just south of the equator. The granitic islands of the Seychelles represent mountain tops of the largely submerged Mahé microcontinent that was separated from Gondwana approximately 65 million years ago and evolved in isolation thereupon. Six plant species were studied – Intsia bijuga, Vateriopsis seychellarum, Pisonia grandis, Pisonia sechellarum, Pinus caribea and Eucalyptus robusta. P. caribea and E. robusta are introduced to the Seychelles, while the other species are native or even endemic (V. seychellarum and P. sechellarum). The mycorrhizal status of P. sechellarum was not known before. Fungal species from the roots were determined by using molecular methods. All studied plants possessed EcM root tips, except P. sechellarum that was forming arbuscular mycorrhiza. Altogether we found 37 EcM fungal species from the roots of different plants. V. seychellarum hosted the most EcM fungal species (15 spp.) while P. grandis and P. caribea the least (three spp. for both). The detected overall species richness is low compared with the other tropical and temperate regions probably caused by long-term isolation and ex¬ten¬¬sive removal of natural vegetation. The most species rich fungal taxa were Thelephorales, Agaricales and Boletales that are also the most common and diverse in other tropical and temperate fungal communities. Introduced E. robusta had common EcM fungi with I. bijuga and V. seychellarum while P. caribea did not share its fungal partners. P. caribea was introduced as seedlings and probably was already associated with EcM fungi, it seems that these fungi are not able to associate with native plants and at the same time P. caribea cannot form mycorrhiza with local fungi. Also native P. grandis possessed distinctive fungal partners (only Tomentella spp.) probably due to unique environmental conditions of the habitat - large amount of N and P amendment to the soil as bird guano makes the soil conditions unusual for the EcM fungi that are common in nutrient-poor soils. It seems that P. grandis is associated with a narrow range of EcM fungi throughout its area. In addition, fungal fruit-bodies were collected from the sampling sites and nine new Tomentella species were described: Tomentella pisoniae, Tomentella tedersooi, Tomentella parmastoana, Tomentella hjortstamiana, Tomentella tenuis, Tomentella beaverae, Tomentella pileocystidiata, Tomen¬tella larssoniana, Tomentella intsiae.