Viktor Oláh

Short-term chromium(VI) stress induces different photosynthetic responses in two duckweed species, Lemna gibba L. and Lemna minor L.

Physiological responses of two duckweed species, Lemna gibba and Lemna minor, to hexavalent chromium [Cr(VI)] were studied in axenic cultures using short-term (48 h) treatments by K2Cr2O7 (0–200 μM). Chlorophyll (Chl) fluorescence parameters and photosynthetic pigment composition of plants were screened to determine the effects of Cr(VI) exposures. The two duckweed species exhibited different sensitivity in the applied Cr(VI) concentration range. Chl fluorescence parameters of dark-adapted and light-adapted plants and electron transport inducibility were more sensitive to Cr(VI) in L. minor than in L. gibba. We also found fundamental differences in quantum yield of regulated, Y(NPQ), and nonregulated, Y(NO), non-photochemical quenching between the two species. As Cr(VI) concentration increased in the growth medium, L. minor responded with considerable increase of Y(NPQ) with a parallel significant increase of Y(NO). By contrast, in L. gibba only 200 μM Cr(VI) in the growth medium resulted in elevation of Y(NPQ) while Y(NO) remained more or less constant within the regarding Cr(VI) concentration range during 48 h. Photosynthetic pigment content did not change considerably during the short-term Cr(VI) treatment but decrease of Chl a/b and increase of Car/Chl ratios were observed in good accordance with the changes in Chl fluorescence parameters. The data suggest that various duckweed species respond with different sensitivity to the same ambient concentrations of Cr(VI) in the growth medium, and presumably to other environmental stresses too, which may have an influence on their competitive relations when heavy metal pollution occurs in aquatic ecosystem.

Carotenoid composition and photochemical activity of four sandy grassland species

The photosynthetic pigments and photochemical efficiency of photosystem 2 (PS2) were studied in four constitutive species (Achillea millefolium L., Festuca pseudovina Hack. ex Wiesb., Potentilla arenaria Borkh., and Thymus degenianus Lyka) of a semiarid grassland in South-eastern Hungary. Every species displayed typical sun-adapted traits and substantial plasticity in the composition and functioning of the photosynthetic apparatus. The contents of chlorophylls (Chls) and carotenoids (Cars) on a dry matter basis declined from May to July, however, the amount of total Cars on a Chl basis increased. This increase was the largest in Potentilla (48 %) and the smallest in Achillea (14 %). The pool of xanthophylls (VAZ) was between 25 % and 45 % of the total Car content and was larger in July than in May. The content of β-carotene increased by July, but lutein content did not change significantly. The Chl fluorescence ratio Fv/Fm was reduced by 3–10 % at noon, reflecting the down-regulation of PS2 in the period of high irradiance and high temperature. The occurrence of minimal values of ΔF/Fm’ showed close correlation to the de-epoxidation rate of violaxanthin. Hence in natural habitats these species developed a considerable capacity to dissipate excess excitation energy in the summer period in their photosynthetic apparatus through the xanthophyll cycle pool and a related photoprotective mechanism, when the photochemical utilization of photon energy was down-regulated.

Comparative study on the sensitivity of turions and active fronds of giant duckweed (Spirodela polyrhiza (L.) Schleiden) to heavy metal treatments.

Standard ecotoxicological test procedures use only active forms of aquatic plants. The potential effects of toxicants on vegetative propagules, which play an important role in the survival of several aquatic plant species, is not well understood. Because turion-like resting propagules overwinter on the water bottom in temperate regions, they could be exposed to contaminants for longer periods than active plants. Due to its turion producing capability, giant duckweed (Spirodela polyrhiza) is widely used in studying morphogenesis, dormancy, and activation mechanisms in plants. It is also suitable for ecotoxicological purposes. The present work aims to compare the growth inhibition sensitivity of active (normal frond) and overwintering (turion) forms of S. polyrhiza to concentrations of nickel (Ni), cadmium (Cd) and hexavalent chromium (Cr) ranging from 0 to 100mgL(-1). The results indicated that in general, resting turions have higher heavy metal tolerance than active fronds. Cd proved to be the most toxic heavy metal to S. polyrhiza active frond cultures because it induced rapid turion formation. In contrast, the toxicity of Ni and Cr were found to be similar but lower than the effects of Cd. Cr treatments up to 10mgL(-1) did not result in any future negative effects on turion activation. Turions did not survive heavy metal treatments at higher concentrations of Cr. Cd and Ni treatments affected both the floating-up and germination of turions but did not significantly affect the vigor of sprouts. Higher concentrations (of 100mgL(-1)) Cd completely inhibited germination.

Characterization of the aodA, dnmA, mnSOD and pimA genes in Aspergillus nidulans

Mitochondria play key roles in cellular energy generation and lifespan of most eukaryotes. To understand the functions of four nuclear-encoded genes predicted to be related to the maintenance of mitochondrial morphology and function in Aspergillus nidulans, systematic characterization was carried out. The deletion and overexpression mutants of aodA, dnmA, mnSOD and pimA encoding alternative oxidase, dynamin related protein, manganese superoxide dismutase and Lon protease, respectively, were generated and examined for their growth, stress tolerances, respiration, autolysis, cell death, sterigmatocystin production, hyphal morphology and size, and mitochondrial superoxide production as well as development. Overall, genetic manipulation of these genes had less effect on cellular physiology and ageing in A. nidulans than that of their homologs in another fungus Podospora anserina with a well-characterized senescence. The observed interspecial phenotypic differences can be explained by the dissimilar intrinsic stabilities of the mitochondrial genomes in A. nidulans and P. anserina. Furthermore, the marginally altered phenotypes observed in A. nidulans mutants indicate the presence of effective compensatory mechanisms for the complex networks of mitochondrial defense and quality control. Importantly, these findings can be useful for developing novel platforms for heterologous protein production, or on new biocontrol and bioremediation technologies based on Aspergillus species.

The Effects of Climate Change on Element Content and Soil pH (Síkfőkút DIRT Project, Northern Hungary)

In the Detritus Inputs and Removal Treatment (DIRT) field experiments established at the Sikfőkut Site (northern Hungary) in October 2000, an experimental approach was applied to study long-term effects of litter quality and quantity on pH and nutrient mobility of soil in a Quercetum petraeae-cerris forest. Our previous results have suggested that decreases in organic matter content, total N, Ca2+ and Mg2+ concentrations in the soil are the consequence of the reduction in forest litter production induced by climate change and the resultant soil degradation over a longer period. An eight-year litter manipulation demonstrated a relation between soil pH and Mg2+ and Ca2+ concentrations in the soil. The reduction of litter production resulted in a decrease of the soil pH which occurred due to the decreasing Mg2+ and Ca2+ inputs into the soil, and consequent reduction of soil buffering capacity against the acidifying effects of the acidic intermediates of litter decomposition and humus compounds. If the litter production increases as a result of climate change, it should be accompanied by increasing C, total N, Ca2+ and Mg2+ contents in the soil and soil pH, with a positive effect on the soil organic matter and fertility. However, this scenario is rather unlikely as our results indicated decreasing litter production in the measurement period.

Assessment of Giant Duckweed (Spirodela polyrhiza L. Schleiden) Turions as Model Objects in Ecotoxicological Applications

In this study germination of Spirodela polyrhiza (L.) Schleiden (giant duckweed) turions was assessed under cadmium exposure to test applicability of a novel turion-based ecotoxicology method. Floating success of germinating turions, protrusion of the first and subsequent fronds as test endpoints were investigated and compared to results of standard duckweed growth inhibition tests with fronds of the same species. Our results indicate that turions can be used to characterize effects of toxic substances. Initial phase of turion germination (floating up and appearance of the first frond) was less sensitive to Cd treatments than the subsequent frond production. The calculated effective concentrations for growth rates in turion and normal frond tests were similar. Single frond area produced by germinating turions proved to be the most sensitive test endpoint. Single frond area and colony disintegration as additionally measured parameters in normal frond cultures also changed due to Cd treatments but the sensitivity of these parameters was lower than that of growth rates.

Seasonal and diurnal variability in sap flow intensity of mature sessile oak (Quercus petraea (Matt.) Liebl.) trees in relation to microclimatic conditions.

In this study sap flow dynamics of mature sessile oak trees (Quercus petraea) in a marginal sessile oak-turkey oak forest was investigated in 2009. That year spring was dry without significant rain in April and May and the driest month was August. Due to the extreme weather conditions the volumetric soil water content (SWC) of upper 30 cm was low on experimental days in May (0.13-0.14 cm3 cm-3) but it reached the lowest value in August (0.08 cm3 cm-3). Sap flow was measured in a dominant and a co-dominant tree by heat dissipation method from 26 March till 30 October. In the present paper several three-day long periods of the continuous seasonal recordings were chosen to represent the effects of typical weather conditions and different stages of canopy development on sap flow dynamics. The daily maximum sap flow density values of dominant and co-dominant trees were similar (0.30-0.32 cm3 cm-2 min-1) in moist period (July). Rains and transient increase of SWC after proceeding drought resulted in change of diurnal course of sap flow in experimental days of July. In this period dominant trees also showed considerable sap flow (0.19 cm3 cm-2 min-1) during night hours and short sap flow peaks in early morning (6:00 to 8:00 a.m.) indicating the refilling of desiccated tissues. After the progressive drought in August the daily maximum sap flow density decreased to 0.07 cm3 cm-2 min-1 in dominant tree and to 0.12 cm3 cm-2 min-1 in the co-dominant. Both trees exhibited gradual stomatal closure from morning hours.

Anthocyanins: possible antioxidants against Cr (VI) induced oxidative stress in Spirodela polyrrhiza.

Rural economy in Croatia with your small sized sector of peasant enterprises still stays in the shadow of restructuring of large industrial sector. The slow leading process of privatization, the wandering in the claim the best solution in agricultural development, absence of consensus about key development priorities, as well as common indicators of backwardness, are only part of gray scale of problems which dented the continue pauperization of wide rural area in Croatia. The Croatian government administration late with implementation of new rural policy measures, which are recommended by Council Regulation (EC) No 1257/1999. This act emphasis the balanced development of the countryside alongside the market support measures in the lights of the social and territorial cohesion. It is based on the following principles: recognising the multifunctional role of agriculture, improving competitiveness, ensuring that environmental issues are taken into account, diversifying economic activity, and conserving rural heritage. In the past time new rural policy in Croatia is considered below local and regional development programs, where the LEADER approach take important role. This is result of pre-accession process to EU and new possibilities of using considerable financial support in IPA subsidy program 2007- 2113.

Springtime Leaf Development of Mature Sessile Oak Trees as Based on Multi-Seasonal Monitoring Data

Abstract - Based on a four year leaf growth data-set we modelled the thermal time-dependent leaf ontogeny in upper and lower canopy layers of mature sessile oak trees, in a Quercetum petraeae-cerris forest stand (NE Hungary). Our regression models revealed no considerable differences between the timing of leaf unfolding and leaf expansion of different canopy layers. On the other hand seasonal course in leaf mass-to-area ratio (LMA) indicated that sun leaves needed considerably longer thermal time to fully develop their anatomical structures compared to shade leaves. LMA of sun leaves was higher during the whole leaf maturation process suggesting that ‘sun’ and ‘shade’ characteristics develop in very early stage of leaf ontogeny. Functioning of photosynthetic apparatus (Fv/Fo) in shade leaves have built up faster and performed better in all developmental stages which could be attributed to two main factors: 1) very early determination of leaf traits as a function of light environment and 2) evolving shading effect of upper canopy layer eliminates photoinhibition in lower leaves. Kivonat - Levélnövekedés és a fotokémiai hatékonyság tavaszi felépülése kocsánytalan tölgyfák lombkoronájában, többéves monitoring adatok alapján. Jelen munkánk során több levéljellemző változása alapján modelleztük a levélfejlődés folyamatait a hőösszeg függvényében, egy mérsékelt övi cseres-tölgyes erdőállomány idős kocsánytalan tölgyfáinak alsó és felső lombkorona-rétegében. Az eredményeink alapján a levélterület kialakulása a lombkorona alsó és felső részében egyszerre kezdődik és fejeződik be. A fénylevelek esetében a levéltömeg/terület arány (LMA) később érte el a nyári értékét, és a levélfejlődés minden szakaszában nagyobb vastagságot és/vagy nagyobb sűrűséget jelzett, ami a fény- és árnyéklevél-tulajdonságok igen korai kialakulását jelzi. A levelekben a PSII kvantumhozam (Fv/Fo) szezonális fejlődését szintén befolyásolja a lombkorona-helyzet. Az árnyéklevelek a teljes fejlődési folyamat alatt magasabb Fv/Fo értékekkel rendelkeztek, és gyorsabban elérték a szezonális maximumukat, mint a fénylevelek, Az utóbbi eredmények szintén a fény- és árnyékjelleg korai determinációjára utalnak, továbbá jelzik azt is, hogy a levélterület-növekedéssel párhuzamosan kialakuló önárnyékolás sietteti a PSII kvantumhozam felépülését.

Retrospective analyses of archive phytotoxicity test data can help in assessing internal dynamics and stability of growth in laboratory duckweed cultures

High growth potential of duckweed species (Lemnaceae family) has been utilized in wide range of research and practical applications. Based on literature data, however, it can be assumed that duckweed populations maintain constant growth rates only when short periods are considered but can vary over longer time scales. This intrinsic instability in growth can affect the interpretation of growth data. Duckweed phytotoxicity tests are usually performed according to highly standardized protocols. Therefore the archive data provide an opportunity for retrospective comparisons. In the present study we collected growth (frond number- and frond area-based relative growth rates) and morphology (average frond and colony sizes) data from control treatments of phytotoxicity tests. All the analyzed tests were carried out with the same Spirodela polyrhiza (L.) Schleid. (giant duckweed) clone (RDSC ID No. 5501) under the same experimental conditions over more than four years. We aimed to assess the overall variability of the above parameters and to test if intrinsic growth patterns affect growth data in short-term. In general, the results reflected high stability of the measured parameters in long term but also indicated that some temporal variability is inevitable which can bias the comparability of growth tests. The frond area-based relative growth rate resulted in smaller coefficient of variation than the usually preferred frond number-based one. The results also revealed a negative correlation between mean growth rates and their coefficients of variation. Therefore, it would be advisable to introduce higher minimal growth rates and/or maximized tolerable coefficients of variation for control cultures into the standard duckweed growth inhibition tests. Analyses of growth data aggregated on seasonal basis indicated faster growth and larger mean frond size in laboratory duckweed cultures from mid-autumn till mid-spring than during summer and early autumn. But, in shorter term (∼50 days) we did not observe distinct trends in growth suggesting that the successive frond generations have no effect on growth traits within this time-scale. Our results point to the importance of assessing intrinsic growth dynamics in duckweed cultures and also to the re-usability of the already collected phytotoxicity data in addressing new research questions.