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Algae are predominantly aquatic organisms that must be able to discriminate between essential and non-essential heavy metal ions (Perales-Vela et al. 2006). Many of the trace metals are essential but toxic at elevated concentrations. Cobalt (Co 2+ ), although an essential element (Lustigman et al. 1995), seems to have a direct effect on P680 (El-Sheekh et al. 2003). According to El-Sheekh et al. (2003) higher Co 2+ concentrations had an inhibitory effect on O 2 uptake by the two algal species Monoraphidium minutum and Nitzchia perminuta. Zinc (Zn 2+ ) is also an essential metal and at elevated concentrations can be toxic and cause algal cell death. Hirata et al. (2001) established that in marine green algae Dunaliella tertiolecta glutathione and phytochelatins can be involved in Zn detoxification. Mercury (Hg 2+ ), a toxic but non-essential element, is a metal with redox capacity that can enhance the pro-oxidant status by reducing the antioxidant glutathion pool (Okamoto et al. 2001). Cadmium (Cd 2+ ) has no known biological functions and is a highly toxic metal to aquatic organisms. Some previous studies demonstrated that Cd can be a substitute of Zn in marine phytoplankton (Price and Morel 1990). Nickel is one of the toxic metals found in industrial wastewaters (Lustigman et al. 1995). Nickel caused reduction in dry weight and at the same time highly stimulated biosynthesis of sulfur containing amino acids in N. perminuta probably due to some chelating mechanisms against heavy metal toxicity (Osman et al. 2004).As pointed out in the paper of Pavlić et al. (2006) microplate algal assays for freshwater algae offer many advantages over standard Erlenmeyer flask tests. A similar procedure was developed for marine algae. Lukavský and Simmer (2001) miniaturized the ISO 10253 bioassay with the marine diatom Phaeodactylum tricornutum by using immunological plates with wells of 0.25 and 2.5 ml as cultivation vessels. Diatoms occupy a variety of habitats and are often the most abundant photosynthetic organisms in marine waters. P. tricornutum is one of the most used algal species in the marine bioassays because of its easy cultivation, it is also a prospective alga in aquaculture as food for, e.g., crustacean Artemia (Kvíderová and Lukavský 2003). Therefore, in this study we have investigated the influence of different heavy metals (Ni 2+ , Co 2+ , Zn 2+ , Cd 2+ and Hg 2+ ) on the growth rate of marine phytoplankton diatom P. tricornutum Bohlin (Bacillariophyceae) by miniaturized bioassay method. Materials and MethodsThe toxicity tests were carried out with the unicellular marine diatom P. tricornutum Bohlin 1897 strain CCAP 1052/1A obtained by Culture Collection of Algae and Protozoa, UK. The alga was cultivated at the Department of Biology, J. J. Strossmayer University in Osijek in the f/2 medium at 20°C under continuous white light exposed to irradiance by PAR 120 lmol m -2 s -1 measured with flat sensor. The basic design of toxicity tests followed the International Standard ISO 10253 marine algal growth inhibition te...

The algal growth potential (AGP) in water samples of the Danube wetland waters (1388-1426 r. km) as well as the effect of nitrogen (in final concentration of 0.16 g l )1 ) and phosphorus enrichment (in final concentration of 0.02 g l )1 ) on the AGP was investigated by miniaturized bioassay method. Values of the total biomass of Chlorella kessleri up to the 14th day of incubation were suitable for the evaluation of trophic conditions according to the classification of AGP. On the basis of the AGP results, trophic conditions in 55% of the samples were oligo-mesotrophic and in 46% of the samples meso-eutrophic. A statistically significant correlation (r=0.34) was established between the AGP of C. kessleri in original water samples and NO 3 concentrations in situ. The TN/TP ratio in the wetland waters indicated a greater limitation due to nitrogen than phosphorous. Significantly lower TSI TN than TSI SD , TSI Chla and TSI TP indicated nitrogen limited conditions. In order to quantify established nutrient limitation by the bioassay method, the effect of added N and P concentrations on the growth rate of C. kessleri was expressed as the degree of nutrient limitation (Dr d )1

The importance of nutrients as limiting factors might vary in environments with different limnological characteristics. In this article we evaluate the effect of frequency and duration of flooding on nutrient limitation in a riparian floodplain. Variations in N and P limitations were studied in the period of low (2003) and high (2004) water level in two different floodplain habitat types in the Nature Park Kopački Rit (Croatia), a floodplain area of the Danube River. In 2003 and 2004, the limnological characteristics of floodplain lake (Lake Sakadaš) and the channel (Stara Drava) differed due to their hydrological regimes. Potential for nutrient limitation was determined by DIN:TP and TN:TP ratios, while the actual nutrient limitation was assessed by nutrient enrichment bioassay. A change from non-limited to N-limited conditions in the channel, and consistent actual N limitation in the lake was determined by the nutrient enrichment experiment. Of the two ratios, DIN:TP matched better with the bioassay data. Phosphorus limitation was only occasionally evident. Changes in trophic conditions from hypereutrophy to eutrophy (between low and high water levels) reflected the importance of the hydrologic regime as a factor which can modify the trophic state of Lake Sakadaš. Compared with 2003, the increase of total nitrogen concentrations in 2004 calls attention to the importance of nitrogen inputs from the Danube to the system with excessive phosphorus concentrations.

This study aimed to screen different winter wheat genotypes at the onset of metabolic changes induced by water deficit to comprehend possible adaptive features of photosynthetic apparatus function and structure to physiological drought. The drought treatment was the most influential variable affecting plant growth and relative water content, and genotype variability determined with what intensity varieties of winter wheat seedlings responded to water deficit. PEG-induced drought, as expected, changed phenomenological energy fluxes and the efficiency with which an electron is transferred to final PSI acceptors. Based on the effect size, fluorescence parameters were grouped to represent photochemical parameters, that is, the donor and acceptor side of PSII (PC1); the thermal phase of the photosynthetic process, or the electron flow around PSI, and the chain of electrons between PSII and PSI (PC2); and phenomenological energy fluxes per cross-section (PC3). Furthermore, four distinct clusters of genotypes were discerned based on their response to imposed physiological drought, and integrated analysis enabled an explanation of their reactions’ specificity. The most reliable JIP-test parameters for detecting and comparing the drought impact among tested genotypes were the variable fluorescence at K, L, I step, and PITOT. To conclude, developing and improving screening methods for identifying and evaluating functional relationships of relevant characteristics that are useful for acclimation, acclimatization, and adaptation to different types of drought stress can contribute to the progress in breeding research of winter wheat drought-tolerant lines.