Elodea plants (Elodea (Egeria) densa Planch.) were incubated in the presence of individual and mixed 1 µM sulfate salts of Ni, Cd, Cu, Zn, and Mn to study the influence of heavy metals (HM) on shoot growth, structural-and functional parameters of the photosynthetic apparatus, lipid peroxidation, enzymatic activities of the antioxidant defense system (superoxide dismutase and catalase), and the content of non pro tein and protein thiols in leaves. The accumulation of HM in leaves decreased in a row: Mn > Cu > Cd > Zn > Ni. The largest reduction in chlorophyll content was caused by Mn and Cu, whereas the strongest reduction in carotenoid content was induced by Cu. The presence of Cu produced the largest decrease in the maximal quantum efficiency of photosystem II (PSII) (F v /F m ). These changes were paralleled by the shift of the pro /antioxidant balance towards the dominance of oxidative processes. The presence of Cd elevated the content of chlorophyll and carotenoids without altering the photochemical efficiency of PSII; Cd retarded the shoot growth but had no appreciable effect on leaf mesostructure. The addition of the second metal to the growth medium alleviated in most treatments the detrimental action of individual ions owing to the enhanced activities of SOD and catalase and because of the significant increase in the content of non protein thiols. It is supposed that the observed antagonism of metal ions is related to their competitive interactions restricting the entry of HM into the cell.Keywords: Elodea (Egeria) densa, heavy metals, oxidative stress, antioxidant enzymes, photosynthetic appa ratus, chlorophyll fluorescence, non protein and protein thiols.Abbreviations: CAT-catalase; DTNBA-5,5' dithiobis(2 nitrobenzoic) acid; GSH-reduced glutathione; HM-heavy metals; NBT-nitroblue tetrazolium; PSII-photosystem II; SOD-superoxide dismutase; TBA-thiobarbituric acid; F v /F m -maximal quantum yield of PSII photoreaction.

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The objective of this study was to compare ecophysiological and morphological parameters of a regionally endangered orchid species, Epipactis atrorubens (Hoffm. ex Bernh.) Bess., growing in two forest communities (on serpentine and granite outcrops) of the Middle Urals, Russia. Biodiversity, dominance, and phytocoenosis studies showed the colonization of a wide range of plant species on both sites. The physicochemical properties of the soil, chemical composition and morphological features of E. atrorubens, growing under technogenic conditions (asbestos deposits), on serpentine outcrops and in the natural environment of the granite massif were studied for the first time. The serpentine substrate differed from the granite one by its greater stoniness, circumneutral pH and lower contents of available nitrogen and phosphorus. Extremely high concentrations of magnesium were found in the serpentine soil, some 79 times higher than in the granite substrate. High concentrations of nickel (94 times), chromium (59 times), cobalt (17 times), and iron (4 times) were found in the serpentine substrate, higher than in the granite substrate. The differences between the sites for available metal contents and for root and shoot metal contents were significantly less. Concentrations of most of the metals in the roots were higher than in the shoots. Despite higher metal concentrations and lower nitrogen and phosphorus levels in serpentine soils, E. atrorubens had a larger population and greater viability compared to those growing on granite. Plants on serpentine outcrops were characterized by the formation of a larger number of fruits, greater root lengths and thicker leaf blades, compared to plants on granites. The well-developed orchid mycorrhizae contributed to the survival of this species under unfavorable serpentine conditions. Hence, serpentine outcrops formed due to the mining of asbestos could be a suitable substrate for the light-demanding E. atrorubens due to its capacity to adapt to dry, rocky, nutrient-depleted soils and limited competition from other plants.

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Aquatic macrophytes, viz. Sagittaria sagittifolia L., Lemna gibba L., Elodea canadensis Michx., Batrachium trichophyllum (Chaix.) Bosch., Ceratophyllum demersum L. and Potamogeton sp. (P. perfoliatus L., P. alpinus Balb., P. crispus L., P. berchtoldii Fieber, P. friesii Rupr., P. pectinatus L.) were collected from 11 sites for determining their metal accumulation and thiols content. Cu(2+), Ni(2+), Mn(2+), Zn(2+), and Fe(3+) exceeded maximum permissible concentrations in chosen sites. Significant transfer of metals from water to leaves is observed in the order of Ni(2+) < Cu(2+) < Zn(2+) < Fe(3+) < Mn(2+). The maximum variation of bioconcentration factor was noticed for manganese. The accumulation of heavy metals in leaves was correlated with non-protein and protein thiols, confirming their important role in metal tolerance. The largest contribution was provided by Cu(2+) (on the average r = 0.88, p < 0.05), which obviously can be explained as an important role of these ions in thiols synthesis. Increased synthesis of thiols in the leaves allows the usage of SH-containing compounds as biomarkers of metal tolerance. Considering accumulation of metals and tolerance, B. trichophyllum, C. demersum and L. gibba are the most suitable species for phytoremediation of highly multimetal contamination, while E. canadensis and some species of Potamageton are suitable for moderately metal-polluted sites.

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In previous decades, some species of the Orchidaceae family have been found growing in man-made habitats. Neottia ovata is one of the most widespread orchids in Europe, however it is quite rare in Russia and is included in several regional Red Data Books. The purpose of this study was to compare the chemical composition and morphophysiological parameters of N. ovata from two forest communities of the Middle Urals, Russia: natural and transformed (fly ash dump of Verkhnetagil’skaya Thermal Power Station) for determining orchid adaptive features. The content of most of the studied metals in the underground parts (rhizome + roots) of N. ovata was considerably higher than in the leaves, which diminished the harmful effect of toxic metals on the aboveground organs. The adaptive changes in the leaf mesostructure of N. ovata such as an increase in epidermis thickness, the number of chloroplasts in the cell, and the internal assimilating surface were found for the first time. The orchids from the fly ash deposits were characterized by a higher content of chlorophyll b and carotenoids than plants from the natural forest community that evidenced the compensatory response on the decrease in chlorophyll a. The ability of N. ovata from the transformed habitat to maintain a relatively favorable water balance and stable assimilation indexes further contribute to its high viability. The study of orchid adaptive responses to unfavorable factors is necessary for their successful naturalization and introduction into a new environment.

Urea being a fertilizer is expected to be less toxic to plants. However, it was found that urea at 100 mg L(-1) caused the oxidative stress in Elodea leaves due to the formation of reactive oxygen species (ROS) and lipid peroxidation that are known to stimulate antioxidant pathway. Urea at a concentration of 500 and 1000 mg L(-1) decreased low-molecular-weight antioxidants. In this case, the antioxidant status of plants was supported by the activity of antioxidant enzymes such as superoxide dismutase and guaiacol peroxidase. A significant increase in the soluble proteins and -SH groups was observed with high concentrations of urea (30-60 % of control). Thus, the increased activity of antioxidant enzymes, low-molecular-weight antioxidants, and induced soluble protein thiols are implicated in plant resistance to oxidative stress imposed by urea. We found that guaiacol peroxidase plays an important role in the removal of the peroxide in Elodea leaves exposed to 1000 mg L(-1)of urea.