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  • Author or Editor: Z. Nagy x
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Stand and leaf scale responses of loess grassland swards to elevated air CO 2 concentration had been investigated in a mini FACE system during 1998–2000. The study concentrated on biomass, leaf area index (LAI) and vegetation surface temperature (stand scale) and on diurnal carbohydrate pattern and gas-exchange responses (leaf scale). Leaf net CO 2 uptake under prolonged exposure to elevated CO 2 showed an upward response in the dicotyledonous and a downward one in the monocotyledonous species. Dawn and evening carbohydrate levels in leaves suggested growth stimulation of the dicot under elevated CO 2 and the opposite for the grass species and indicated sink limitation as a major factor determining photosynthetic acclimation at the species level. The smaller LAI as well as the insignificant biomass response to elevated air CO 2 was a compounded response by multi-species stands. Under mild water shortage, elevated air CO 2 concentration partly alleviated the drought effect shown by the higher relative growth rate of LAI. Canopy surface temperatures of the vegetation in the CO 2 enriched rings were higher than those in the ambient rings suggesting that decreased leaf conductance and transpiration were responsible for the temperature difference between the treatments. Increased canopy surface temperature under elevated air CO 2 concentration will probably lead to increased sensible heat flux and therefore enhanced convection at larger spatial scales.

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The aim of the present work was to study the soil seed bank of the semiarid sandy grassland community using the nested sampling procedure. The samples consisted of six concentric cores with diameters ranging from 5 to 22 cm and surface area ratio of the outermost to the innermost ring of 19. Investigations were directed to establish the minimum core diameter to find the dominant and less frequent species in the seed bank and also to have an insight on distribution patterns of species. The smallest core (diameter: 5 cm) employed in 20 repetitions was adequate to find the dominant species in the seed bank, while increasing the sample area to 19 times resulted in doubling the number of species found. The seeds of the dominant species had clustered distribution even at the smallest applied sample scale, while patterns of seed clumps followed different (uniform, contagious, random) distributions.

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The effects of UV-C radiation on the germination rate and fungal contamination of tall fescue seeds were investigated. Samples from the same seed lot were irradiated in two different ways in two consecutive years. The seeds were irradiated with a Hg vapour lamp using different doses. In the first trial one side of the seeds was irradiated, while in the second trial a mirror was used to irradiate the whole seed surface. The results showed that various doses of UV-C irradiation had an effect on the germination rate, but there were no significant differences in germination percentage between the treatments. Differences in fungal contamination rates were observed when the seeds were irradiated on all sides. The presence of 21 fungal genera was identified on the seeds, the saprotrophic fungi Alternaria, Rhizopus and Penicillium being dominant.

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The survey was carried out on the seed bank of several patches of an open, semiarid sandy grassland (Festucetum vaginatae Rapaics ex Soó 1929 (Borhidi 1996)). We chose four, approximately 20 m × 20 m large, adjacent patches, different in their species composition and total cover. Soil samples were taken in early spring and at the end of summer, in two consecutive years. We determined the seed bank of the samples with the seedling emergence method. The fact that we found the seeds of only two species that were not present in the vegetation indicates the isolated and without artificial disturbed state of the grassland. The vegetation and the seed bank of the patches showed a low degree of similarity in the same period, while the composition of the spring aspect reflected clearly in the seed bank of late summer in all four patches. Results showed that mosaic-like appearance is not only characteristic of the vegetation, but also the seed bank of the soil. Differentiation of the seed bank manifested mostly after the period of seed-fall, at the end of summer, while in early spring it was less expressed. On the basis of the differentiation of the seed bank we can conclude that not the dispersion of seeds, but natural vicinity of mother plants was decisive in forming the spatial variation of the seed bank.

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Although angiogenesis is considered to be indispensable for continuous tumour growth, only very few studies have been published performing microvessel quantification during tumour progression. We mea- sured the tumour vascularity in different stages of rat pancreatic carcinogenesis induced by azaserine and promoted by raw soya flour-containing pancreatotrophic diet. Besides the tumour samples taken at 6 (atypical acinar cell nodules), 15 (adenomas) and 20 (localised adenocarcinomas) months after carcino- gen initiation, we also investigated 3 control groups: tumour-bearing host tissue of azaserine-treated rats and normal tissue of untreated rats kept on standard or pancreatotrophic diet. In contrast with the usual microvessel counting on hot spots, we determined microvascular surface density (SV) and volume den- sity (VV) by electron microscopic morphometry. There was no significant difference in these respect between the control groups. At month 6 after the azaserine induction SV and VV showed slight, non- significant decrease as compared to the host control. Both values remained unchanged until the 15th month and increased significantly by the 20th month. These results may indicate comparable growth rate of tumour and new microvessels in the premalignant stages of carcinogenesis while a more intense angio- genesis than tumour growth afterwards.

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In vitro shoot multiplication of Telekia speciosa (Schreb.) Baumg. was tested on media containing benzyladenine, benzyladenine riboside, kinetin, zeatin, meta-topolin or 2-isopentenyladenine in different concentrations. We observed the proliferation rate, the length of shoots, rate of callus formation, and the presence of the hyperhydricity. The highest proliferation rate (13.17) was obtained on medium supplemented with 5.0 μM benzyladenine, however, the leaves were hyperhydrated at this concentration of benzyladenine, therefore for shoot multiplication lower (1.0 μM BA) concentration of benzyladenine is suggested. The longest shoots were achieved using 1.0 μM 2-iP. At this treatment 100% rooting was found, therefore the stage of rooting is omissible using 1.0 μM 2-iP during the multiplication. This in vitro propagation protocol should be useful for conservation as well as mass propagation of this plant species.

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The carbon balance of the sandy pasture (Bugac) and the mountain meadow (Mátra) varied between −171 and 96 gC m−2 year−1, and −194 and 14 gC m−2 year−1, respectively, during the study period (2003–2009). Large part of interannual variability of net ecosystem exchange (NEE) was explained by the variation of the annual sum of precipitation in the sandy grassland ecosystem, while this relationship was weaker in the case of the mountain meadow on heavy clay soil. These different responses are largely explained by soil texture characteristics leading to differences in soil water contents available to plants at the two grasslands. The grassland on heavy clay soil was more sensitive to temporal distribution of rainfall for the same reason. The mountain meadow therefore seems to be more vulnerable to droughts, while the sandy grassland is better adapted to water shortage. The precipitation threshold (annual sum), below which the grassland turns into source of carbon dioxide on annual basis, is only 50–80 mm higher than the 10 years average precipitation sum. In extremely dry years (2003, 2007 and 2009), even the sandy grassland ecosystem was not stable enough to maintain its sink character.

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Phytophthora alni is a species hybrid that causes a destructive root and collar rot disease of alders throughout Europe. Its subspecies, P. alni subsp. alni (Paa), P. alni subsp. uniformis (Pau) and P. alni subsp. multiformis (Pam) can be distinguished on the basis of phenotypic and genotypic traits. In this study, we report evidence of an unusual genomic combination of two subspecies occurring in two P. alni isolates from Hungary. These isolates, which had previously been identified as Paa using hybrid-specific PCR primers and morphological traits, exhibited a mitochondrial DNA restriction pattern identical to that of Pau. However, RAPD patterns and isozyme profiles of nuclear genes encoding glucose-phosphate isomerase (Gpi) and malate dehydrogenase (Mdh) of the two atypical isolates were identical to those found in all Paa isolates. Isozyme analysis also revealed a novel allele at the putative Mdh-1 locus in Paa and Pam isolates. The atypical Paa isolates have likely emerged as a result of hybridization events in the P. alni population between Paa and Pau .

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Growth regulation is a crucial event in tumour progression. Surprisingly, relatively few papers have dealt with the catabolic side of regulation, and there are practically no data regarding the autophagic process during tumour development. We approach this problem by morphometrical investigation into the possi- ble changes of autophagic activity during the progression of rat pancreatic adenocarcinoma induced by azaserine. In the present study, autophagic capacity of the azaserine-induced premalignant and malignant cells were characterised and compared to the respective host tissue cells of the rat pancreas and to the acinar cells in other stages of tumour development. Using vinblastine (VBL) as an enhancer, and cyclo- heximide (CHI) as an inhibitor of autophagic segregation we observed that autophagic capacity of pre- malignant cells (month 6 and 10 after initiation) is much higher than in the host tissue cells. We found a sharp decrease in self-digesting capacity in adenocarcinoma cells (month 20) where VBL induced a min- imal accumulation of autophagic vacuoles which was, surprisingly, not inhibited by CHI, i.e. the CHI- sensitive regulatory step was lost. The changes in autophagic capacity are probably associated to specif- ic steps of tumour progression in our system.

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