No abstract

Rutin is an antioxidant with many interesting pharmacological effects. It can also be found in buckwheat (Fagopyrum esculentum Moench). UV radiation stimulates the activity of enzymes of the phenylpropanoid pathway and there is some evidence that it influences the rutin content in plants. The aim of the present research was (1) to examine the influence of different levels of UV-B radiation on rutin content and (2) to compare the results obtained by three analytical methods. The plants were grown under three UV-B levels: reduced, ambient and enhanced, simulating 17% ozone depletion. Analyses were performed by HPLC and two spectrophotometric methods. In one, the absorbancies were measured at 420 nm with and without the addition of AlCl(3). In another method the concentration was calculated from absorbancies at 352.5 nm and 366.5 nm according to the Official Methods of Analysis of AOAC International. The highest amounts of rutin were found in flowers, followed by leaves and stems. A comparison of the different treatments revealed that the highest amounts of rutin were in plants grown under ambient radiation, followed by the plants cultivated under enhanced UV-B and then under reduced UV-B radiation. Treatments caused more effect on leaves than on flowers. Leaves developed under ambient light conditions contained 97% more rutin than leaves grown under reduced UV-B radiation. In flowers, the contents differed by 19% only. The results obtained using the three methods showed a good correlation, but the absolute differences were surprisingly high. The AOAC and the AlCl(3) methods gave, on average, 140% and 30% higher results than HPLC, respectively.

The effect of enhanced UV-B radiation on buckwheat (Fagopyrum esculentum Moench. variety 'Darja'), an important high elevation crop, was studied in order to estimate its vulnerability in changing UV-B environment. Plants were grown in outdoor experiments from July to October under reduced and ambient UV-B levels, and an UV-B level simulating 17% ozone depletion in Ljubljana. During the development the following parameters were monitored: light saturated photosynthetic activity, transpiration, potential and effective photochemical efficiencies of photosystem II, the contents of photosynthetic pigments and methanol soluble UV-B absorbing compounds. At the end of the experiment, growth rate and production of seeds were estimated. In the following growth season the seeds collected from plants exposed to different UV-B treatments were tested for germination capacity. Total UV-B absorbing compounds during plant development were increased by UV-B radiation, photosynthetic pigments (chlorophyll a and b and carotenoids) decreased. Photosynthetic rate was lowered in an early stage of development. UV-B treatment resulted in the increase in the transpiration rate and consequently the decrease in water use efficiency (WUE). The disturbances in water economy and in photosynthesis affected the reproduction potential negatively; the production of seeds in plants cultivated under ambient and enhanced UV-B was 57 and 39% of the production of specimens treated with reduced UV-B, respectively. The germination of seeds collected from treated plants revealed on average about 95% success, independently of the treatment, but the time needed for germination was the shortest for seeds developed under enhanced UV-B level treatment. Enhanced UV-B radiation affected water relations and production of buckwheat, but not the potential of seeds for germination.

No abstract

The hypothesis of this study is that the variable hydrological regime of intermittent lakes and wetlands affects the primary productivity, decomposition and root fungal colonisation of Phragmites australis, with effects on the whole ecosystem metabolism. The above-ground biomass of reed stands was monitored in littoral and riparian stands of Lake Cerknica, under different water levels. Leaf and culm litter decomposition was also studied at three locations, from predominantly dry to permanently submerged. Root colonisation by fungi was monitored across two seasons in the littoral reed stand. The primary productivity of the littoral stands was related to a variable degree with water levels and air temperature in July in the current year. In the riparian reeds, only monthly temperatures in October of the previous year were important. The submersion duration of the litter enhanced the decomposition rates. The frequency of fungal colonisation of reed roots was decreasing with the submersion time length. Overall, roots were colonised by arbuscules, hyphae, vesicles, hyphal coils and microsclerotia. The main outcomes of this study deals with the role of intermittent hydrological conditions in determining the structure and functioning of reed-dominated lacustrine wetlands, which are exposed to climate threats.

No abstract

The combined effects of UV-B irradiation and foliar treatment with selenium on two buckwheat species, common (Fagopyrum esculentum Moench) and tartary [Fagopyrum tataricum (L.) Gaertn.] buckwheat, that underwent different intensity of breeding, were examined. Plants grown outdoors under three levels of UV-B radiation were studied for 9 weeks, from sowing to ripening. At week 7 they were sprayed with solution containing 1 g(Se) m -3 that presumably mitigates UV-B stress. Morphological, physiological, and biochemical parameters of the plants were monitored. Elevated UV-B radiation, corresponding to a 17 % reduction of the ozone layer, induced synthesis of UV absorbing compounds. In both buckwheat species it also caused a reduction in amounts of chlorophyll a during the time of intensive growth, an effect, which was increased in tartary buckwheat in the presence of selenium. The respiratory potential, measured as terminal electron transport system activity, was lower in plants subjected to enhanced UV-B radiation during the time of intensive growth. The effective quantum yield of photosystem 2 was also reduced due to UV-B radiation in both buckwheat species and was mitigated by the addition of Se. Se treatment also mitigated the stunting effect of UV-B radiation and the lowering of biomass in common buckwheat.

Two cultivars of common buckwheat (Fagopyrum esculentum), Pyra and Siva, were exposed to three treatments: water deficit (WD), foliar spraying by selenium (as Na 2 SeO 4 ) (Se), and the combination of both. In WD-plants the stomatal conductance (g s ) was significantly lower, while WD+Se-plants of Siva had significantly higher g s . None of the treatments resulted in significant differences of potential photochemical efficiency of photosystem 2 (PS2). A significantly higher actual photochemical efficiency of PS2 was obtained in Siva WD-plants and in Pyra Se-and WD-plants which was possibly due to improvement of plant water management during treatment. A significant interaction was observed between the effects of WD and Se on respiratory potential in Pyra. WD, Se, and the WD+Se combination resulted in shorter Pyra and Siva plants, with a reduced number of nodes. WD slightly negatively affected the yield per plant. The yield was highest in plants exposed to Se only. In Siva the number of seeds was triple while the average seed mass remained unchanged.