Exposure Media and Nanoparticle Size Influence on the Fate, Bioaccumulation, and Toxicity of Silver Nanoparticles to Higher Plant Salvinia minima.

Silver nanoparticles (AgNPs) are favoured antibacterial agents in nano-enabled products and can be released into water resources where they potentially elicit adverse effects. Herein, interactions of 10 and 40 nm AgNPs (10-AgNPs and 40-AgNPs) with aquatic higher plant Salvinia minima at 600 µg/L in moderately hard water (MHW), MHW of raised calcium (Ca2+), and MHW containing natural organic matter (NOM) were examined. The exposure media variants altered the AgNPs' surface properties, causing size-dependent agglomeration. The bio-accessibility in the ascending order was: NOM < MHW < Ca2+, was higher in plants exposed to 10-AgNPs, and across all exposures, accumulation was higher in roots compared to fronds. The AgNPs reduced plant growth and the production of chlorophyll pigments a and b; the toxic effects were influenced by exposure media chemistry, and the smaller 10-AgNPs were commonly the most toxic relative to 40-AgNPs. The toxicity pattern was linked to the averagely higher dissolution of 10-AgNPs compared to the larger counterparts. The scanning electron microscopy and X-ray fluorescence analytical techniques were found limited in examining the interaction of the plants with AgNPs at the low exposure concentration used in this study, thus challenging their applicability considering the even lower predicted environmental concentrations AgNPs.

Electrostatic spraying of imazamox to control the floating aquatic plant Salvinia molesta and its effects on environmental indicators of water quality.

This study aimed to assess, in a microcosm condition, the efficacy of electrostatic spraying of herbicide imazamox in the control of Salvinia molesta and the effects of decomposition of plant material on water quality. The herbicide rates used were 600, 700, 800, and 900 g ai ha-1 and spray volume of 50 L ha-1 in electrostatic application. Control effectiveness was assessed at 7, 15, 30, 45, and 60 days after application (DAA), expressed in percentage (0-100%) of visible injury symptoms in the plants, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), chlorophyll a and pheophytin a contents at 0, 7, 15, 30, 45, and 60 DAA, and fresh and dry biomass at 60 DAA. Imazamox was effective in controlling 63% of S. molesta with 900 g ai ha-1 in 45 DAA and 30% with 800 g ai ha-1 in 30 DAA, and reduced 82.3% and 17.5% of fresh weight and 62.6% and 9.3% of dry weight of plant at 60 DAA, respectively. The imazamox spray reduced chlorophyll a with all doses applied and increased BOD5 in 45 DAA with 900 g ai ha-1 and COD in all assessment periods, but for temperature, dissolved oxygen, electrical conductivity, and pH, there was no significant effect after spraying. The herbicide imazamox reduced S. molesta plants with 900 g ai ha-1, without causing significant effects on environmental indicators of water quality. Electrostatic spraying of herbicide can be used in management strategies of aquatic plants to reduce plant density in water bodies and maintain the colonization of plants at a level not harmful to the aquatic biota.

Synergetic enhancement toxicity of copper, cadmium and microcystin-LR to the Ceratophyllum demersum L.

Heavy metals and microcystins commonly co-exist in water bodies with cyanobacteria, and have been shown to affect aquatic plants. However, their combined effects remain largely unknown. In this study, the toxic effects of copper (Cu) and cadmium (Cd) on Ceratophyllum demersum L. were characterized in the presence of microcystin-LR (MC-LR). The results showed that the bioaccumulation of MC-LR and Cu/Cd in C. demersum was significantly increased by the interaction between MC-LR and Cu/Cd. The combined toxicity assessment results suggested that the toxicities of Cu or Cd to C. demersum would be largely exacerbated by MC-LR, which could be the results of increased bioaccumulation of the pollutants. Cu, Cd and MC-LR, as well as their mixture, significantly decreased plant fresh weight and total chlorophyll content of C. demersum, especially at their high concentrations. The antioxidative system was activated to cope with the adverse effects of oxidative stress. Antioxidant enzyme activities were significantly stimulated by Cu, Cd and MC-LR, as well as their mixture. However, the decreased superoxide dismutase (SOD) and glutathione reductase (GR) activities were observed when exposed to relative high concentrations of Cu or Cd together with MC-LR of 5 µg L-1. MC-LR brought more stress to the antioxidative system, which is another possible explanation for the synergistic effect. Our findings highlight increased ecological risks of the co-contamination of heavy metals and harmful cyanobacteria.

Assessing the effects of water quality on leaf morphoanatomy, ultrastructure and photosynthetic pigment content of Salvinia auriculata Aubl. (Salviniaceae).

The objective of this study is to evaluate the effects of physical-chemical and biological variables of the water of the Capibaribe River (state of Pernambuco, Brazil) on leaf anatomy, including ultrastructure and photosynthetic pigment of Salvinia auriculata. Specimens of S. auriculata collected in the Gurjaú River, an area with a low pollution degree, were acclimatized in Hoagland's solution and then subjected to three water samples of the Capibaribe River with different levels of pollution. Twenty-one physical-chemical and biological variables were analyzed according to the Standard Methods for the Examination of Water and Wastewater. The results showed that the samples of the Capibaribe River presented nine parameters that did not comply with the current Brazilian legislation. After 15 days of bioassay, S. auriculata presented variations in mesophyll and cuticle thickness, changes in trichome morphology and accumulation of phenolic compounds. No significant differences were observed for photosynthetic pigment content and leaf length of S. auriculata. Multivariate analyses (PCA and Cluster) showed that the point in the Capibaribe River with the highest number of variables that do not comply with the current legislation was responsible for major structural and chemical changes observed in S. auriculata.

Typha latifolia and Thelypteris palustris behavior in a pilot system for the refinement of livestock wastewaters: A case of study.

In animal livestock heavy metals are widely used as feed additives to control enteric bacterial infections as well as to enhance the integrity of the immune system. As these metals are only partially adsorbed by animals, the content of heavy metals in manure and wastewaters causes soil and ground water contamination, with Zn2+ and Cu2+ being the most critical output from pig livestock. Phytoremediation is considered a valid strategy to improve the purity of wastewaters. This work studied the effect of Zn2+ and Cu2+ on the morphology and protein expression in Thelypteris palustris and Typha latifolia plants, cultured in a wetland pilot system. Despite the absence of macroscopic alterations, remodeling of cell walls and changes in carbohydrate metabolism were observed in the rhizomes of both plants and in leaves of Thelypteris palustris. However, similar modifications seemed to be determined by the alterations of different mechanisms in these plants. These data also suggested that marsh ferns are more sensitive to metals than monocots. Whereas toleration mechanisms seemed to be activated in Typha latifolia, in Thelypteris palustris the observed modifications appeared as slight toxic effects due to metal exposure. This study clearly indicates that both plants could be successfully employed in in situ phytoremediation systems, to remove Cu2+ and Zn2+ at concentrations that are ten times higher than the legal limits, without affecting plant growth.

Lead accumulation and soil microbial activity in the rhizosphere of the mining and non-mining ecotypes of Athyrium wardii (Hook.) Makino in adaptation to lead-contaminated soils.

Better understanding of microbial activity in the rhizosphere soils associated with lead (Pb) uptake by plants may help with the phytoremediation of Pb-contaminated soils. In this work, the effects of Pb exposure (0, 200, 400, 600, 800 mg kg-1) on Pb accumulation and soil microbial activity in the rhizosphere of the mining ecotype (ME) and corresponding non-mining ecotype (NME) of Athyrium wardii (Hook.) Makino were investigated through a pot experiment. Although the plant growth of the two ecotypes was inhibited under Pb stress, the ME showed a less biomass decrease (12.6-44.0%) for aboveground than the NME, showing a greater tolerance to Pb stress. Pb concentrations as well as Pb accumulation in the two ecotypes showed an increasing trend with increasing soil Pb concentrations. The ME presented greater Pb accumulation ability than the NME, especially in underground parts. Pb availability in the rhizosphere soils of the two ecotypes after harvest decreased compared with those before transplantation. Available Pb in the rhizosphere of the ME was 1.4-4.8 times higher than that of the NME under exposure to 200-800 mg kg-1 Pb. The ME shows a greater ability to mobilize Pb in the rhizosphere soils. Pb exposure resulted in an inhibition of microbial activity in the rhizosphere of the two ecotypes. The ME demonstrated greater soil respiration and microbial biomass carbon (MBC) in the rhizosphere than the NME when treated with 200-800 mg kg-1 Pb. The ME showed a less decrease for MBC and a less increase for metabolic quotient in the rhizosphere soils than the NME when exposed to Pb generally. Microorganisms in the rhizosphere soils of the ME seem to be much more adapted to Pb stress, thus showing a great benefit for Pb accumulation and the phytostabilization of Pb-contaminated soils by the ME.

Accumulation of uranium and heavy metals in the soil-plant system in Xiazhuang uranium ore field, Guangdong Province, China.

Plants that have grown for many years in the special environmental conditions prevailing in mining areas are naturally screened and show strong capacity to adapt to their environment. The present study investigated the enrichment characteristics of U and other heavy metals (As, Cu, Pb, Mn, Mo, Zn, Cd, Co, and Ni) in the soil-plant system in Xiazhuang uranium mine. Four dominant plants (Castanopsis carlesii, Rhus chinensis, Liriodendron chinense, and Sapium discolor) and soil samples were collected from the mined areas, unmined areas, and background areas away from the ore field. U, As, Cu, Pb, Mn, Mo, Zn, Cd, Co, and Ni concentrations were analyzed by ICP-MS. The results demonstrate that (1) The highest concentrations of U (4.1-206.9 mg/kg) and Pb (43.3-126.0 mg/kg) with the geoaccumulation index (Igeo) greater than 1 show that they are the main soil pollutants in the research area. (2) The biological accumulation coefficient (LBAC) values for Cd, Mn, and Cu are greater than zero in S. discolor, L. chinense, and C. carlesii and these three plants indicate that they can be used for remediation of the soil in the ore field. (3) R. chinensis inhibits the accumulation of heavy metals and shows sensitive pigment responses to the accumulation of U in the leaves. L. chinense has the strongest enrichment effect on heavy metals but exhibits weak biochemical responses under U stress. C. carlesii demonstrates strong adaptation to U and can maintain healthy pigment characteristics in case of high U enrichment. (4) S. discolor, L. chinense, C. carlesii and R. chinensis have strong tolerance to U toxicity and different biochemical responses.

Effect of daily exposure to Pb-contaminated water on Salvinia biloba physiology and phytoremediation performance.

Lead (Pb) removal from water column was evaluated in batch experiments using naturally occurring Salvinia biloba Raddi (S. biloba) specimens collected from Middle Paraná River and exposed every 24 h to a fresh discharge of water contaminated with 2.65 ± 0.07, 12.62 ± 0.02 or 30.57 ± 0.01 mg L-1 Pb, during 10 consecutive days. S. biloba demonstrated a great ability for metal concentration-dependent Pb removal under these stressful conditions. Additionally, Pb toxicity in plants was assessed by the quantification of physiological parameters in root-like modified fronds (named "roots"), and its aerial leaf-like fronds (named "leaves") of submerged S. biloba. Photosynthetic (carotenoids, chlorophyll a, b, and total) and antioxidant pigments (anthocyanins and flavonoids), soluble carbohydrate content, and membrane stability index of both roots and leaves were affected as the metal concentration increased. In general, root deterioration was more pronounced than that in leaves, suggesting a greater implication of the former organs in Pb removal by S. biloba. All of these deleterious effects were well correlated with qualitative changes observed at plant phenotype during the assay. In conclusion, S. biloba may be considered as a water fern useful in phytoremediation strategies towards management of residual water bodies contaminated with Pb. In addition, these macrophytes could also be valuable for water biomonitoring contributing to improve risk assessments related to metal presence in wastewaters.

Physiological mechanisms of aluminum (Al) toxicity tolerance in nitrogen-fixing aquatic macrophyte Azolla microphylla Kaulf: phytoremediation, metabolic rearrangements, and antioxidative enzyme responses.

To investigate the extent of aluminum toxicity tolerance of eco-friendly, fast-growing, fresh water, pteridophytic Azolla-Anabaena symbiotic association in terms of altered physiological signals; Azolla microphylla Kaulf was exposed to 0 (control), 100, 250, 500, and 750 µM AlCl3, at pH 4.5 for 6 days. The adversity of Al was increased in a dose-dependent manner and the highest was recorded at 750 µM AlCl3. Despite the significant loss in membrane integrity (80% electrolyte leakage) due to an enhanced generation of H2O2, A. microphylla reflected only 50% growth inhibition (fresh and dry weight) at 500 µM AlCl3 (LD50). However, the average root length of Azolla was drastically reduced at high concentration due to their direct contact with aluminum-containing growth medium. Contrary to this, the whole association maintained moderate chlorophyll, carbohydrate content, photosynthetic efficiency, nitrogen-fixing ability, and nitrogen content at high Al concentration. Probably, growth protection was pertained through significant detoxification of H2O2 by employing an efficient antioxidative defense system including antioxidative enzymes (SOD, APX, and CAT) and non-enzymatic antioxidant carotenoids. An enhanced level of phenolics and flavonoids in the root exudates possibly maintained a non-toxic level of aluminum inside the cell (195.8 µg Al/g FW) which makes A. microphylla a suitable pteridophytic plant to not only remove toxic Al from the contaminated sites but also to improve nitrogen status of those regions. Graphical abstract ᅟ.

Changes of DNA methylation of Isoetes sinensis under Pb and Cd stress.

To investigate the molecular response of ancient plants to heavy metal stress and to explore the feature of DNA methylation in endangered plants after exposure to heavy metals, the Isoetes sinensis, an endangered plant, was stressed with three different concentrations of two heavy metals lead (Pb) and cadmium (Cd), respectively. Then the degrees and the patterns of DNA methylation in the leaves were measured on the 14th day using Methylation Sensitive Amplified Polymorphism (MSAP) technique. The results showed that the DNA methylated profile of I. sinensis was affected by Pb and Cd stress. There was no significant difference in the amount of DNA methylation among control check (CK), Pb stress group, and Cd stress group (CK 46.96%, Pb 48.23%, and Cd 48.1%). However, full-methylation level of Pb stress group (28.34%) and Cd stress group (20.25%) was lower than control (33.91%), in contrast, hemi-methylation level Pb stress group (19.89%) and Cd stress group (27.85%) were higher than control (13.04%). The change of patterns from no methylation or hemi-methylation of internal and external cytosines into full-methylation of internal and external cytosines accounted for a large proportion in enhanced methylation aspects. The full-methylation into no methylation or hemi- or full-methylation of internal and external cytosines occupied most of demethylation. The proportion of DNA methylation (including hypermethylation) by both Pb and Cd stresses is nearly equal (39.04% and 39.71%), but the proportion of DNA demethylation by Cd is higher than that by Pb (46.86% than 33.92%).

Macrophytes are highly sensitive to the herbicide diquat dibromide in test systems of varying complexity.

The herbicide diquat dibromide is used in North America to manage nuisance macrophytes. However, its effect on native macrophytes is less clear and it could cause indirect effects on other aquatic biota. This study determined the sensitivity of both native and non-native macrophytes grown in test systems with varying complexity to diquat dibromide applied directly to water following label directions. In an outdoor mesocosm experiment and single species greenhouse concentration-response tests, Elodea canadensis Michx., Myriophyllum spicatum L., Ceratophyllum demersum L. and Hydrocharis morsus-ranae L. were exposed to a range of diquat dibromide concentrations (4.7 - 1153 µg/L), corresponding to 0.4 - 100% of the recommended label rate of the formulated product. The mesocosm experiment contained all four plant taxa in the same system along with caged amphipods (Hyalella azteca Saus.), tadpoles (Lithobates pipiens Schreber), phytoplankton and periphyton; however, this study focuses on the macrophytes only. In both test systems, severe direct effects of diquat dibromide on macrophytes were detected, with almost 100% mortality of all macrophytes in both test systems at 74 µg/L. The most sensitive species in the single species tests, E. canadensis, showed almost 100% mortality at concentrations below the HPLC-based method detection limit of 5 µg/L. Effects occurred very rapidly and showed no difference in severity between native and non-native macrophytes or complexity of test systems. These results suggest that diquat dibromide could be applied at a considerably lower label rate, depending on the characteristics of the waterbody, while still achieving effective control of nuisance macrophytes.

Evaluation of the Relevance of Myriophyllum alterniflorum (Haloragaceae) Cadmium-Sensitive Biomarkers for Ecotoxicological Surveys.

Toxicity caused by trace metal elements in water is a major concern, leading to environmental disturbances and public health problems. The effect of cadmium on clonal macrophyte populations is poorly documented despite its high level of toxicity among aquatic organisms. Our aim here is to highlight the strong relationship existing between the physiological responses of Myriophyllum alterniflorum and the cadmium level over a long exposure period. Nine potential biomarkers of cadmium stress are tested, with three of them appearing to be highly sensitive: free proline, Hsp70, and malondialdehyde. Long-term follow-up analysis after metal exposure (27 days) also proves to be quite beneficial by providing a detailed overview of ecotoxicological events that is more complete and extensive than data recordings conducted over a few days. Taken together, these results support our initial hypothesis that leads to recommending biomarker analyses over at least 2 weeks of metal exposure.

Cd and Pb accumulation characteristics of phytostabilizer Athyrium wardii (Hook.) grown in soils contaminated with Cd and Pb.

Interactions between heavy metals in soil could affect soil heavy metal availability and plant uptake. Thus, in this study, Cd and Pb accumulation as well as plant growth of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii (Hook.) in response to the exposure of Cd and Pb was investigated by a pot experiment. Although the exposure of Cd in combination with Pb further inhibited the growth of the two ecotypes in comparison with the exposure of single Cd or Pb, the ME presented lower biomass decline for the whole plant (22.0%-70.0%) than the NME among most treatments. The presence of Pb promoted Cd accumulation both in above-ground and under-ground parts of the ME. Cd concentrations in under-ground parts of the ME decreased when exposed to higher concentrations of Pb (> 600 mg kg-1). Meanwhile, the presence of Cd inhibited Pb accumulation in above-ground parts of the ME and promoted Pb accumulation in under-ground parts of the ME. Pb concentrations in under-ground parts of the ME decreased when soil Cd concentrations were more than 25 mg kg-1. The partial correlation analysis further demonstrated that the interactions between Cd and Pb stimulated Cd accumulation both in above-ground and under-ground parts of the ME and Pb accumulation in under-ground parts of the ME, while inhibited Pb accumulation in above-ground parts of the ME, showing great benefit for Pb phytostabilization by the ME. Among treatments, the bioaccumulation coefficients for Cd and Pb of the ME, varying from 2.71-31.05 and 20.09-78.06, were much higher than those of the NME. The translocation factors for Cd and Pb of the ME, varying from 0.26-0.52 and 0.01-0.10, were lower than those of the NME. These results indicate that the ME presented greater potential for the phytostabilization of soil contamination with Cd and Pb, especially for Pb.

Hornwort stomata do not respond actively to exogenous and environmental cues.

Backgrounds and Aims: Because stomata in bryophytes occur on sporangia, they are subject to different developmental and evolutionary constraints from those on leaves of tracheophytes. No conclusive experimental evidence exists on the responses of hornwort stomata to exogenous stimulation. Methods: Responses of hornwort stomata to abscisic acid (ABA), desiccation, darkness and plasmolysis were compared with those in tracheophyte leaves. Potassium ion concentrations in the guard cells and adjacent cells were analysed by X-ray microanalysis, and the ontogeny of the sporophytic intercellular spaces was compared with those of tracheophytes by cryo-scanning electron microscopy. Key Results: The apertures in hornwort stomata open early in development and thereafter remain open. In hornworts, the experimental treatments, based on measurements of >9000 stomata, produced only a slight reduction in aperture dimensions after desiccation and plasmolysis, and no changes following ABA treatments and darkness. In tracheophytes, all these treatments resulted in complete stomatal closure. Potassium concentrations are similar in hornwort guard cells and epidermal cells under all treatments at all times. The small changes in hornwort stomatal dimensions in response to desiccation and plasmolysis are probably mechanical and/or stress responses of all the epidermal and spongy chlorophyllose cells, affecting the guard cells. In contrast to their nascent gas-filled counterparts across tracheophytes, sporophytic intercellular spaces in hornworts are initially liquid filled. Conclusions: Our experiments demonstrate a lack of physiological regulation of opening and closing of stomata in hornworts compared with tracheophytes, and support accumulating developmental and structural evidence that stomata in hornworts are primarily involved in sporophyte desiccation and spore discharge rather than the regulation of photosynthesis-related gaseous exchange. Our results run counter to the notion of the early acquisition of active control of stomatal movements in bryophytes as proposed from previous experiments on mosses.

Endocide-Induced Abnormal Growth Forms of Invasive Giant Salvinia (Salvinia molesta).

Giant salvinia (Salvinia molesta) is one of the most noxious invasive species in the world. The fern is known to have primary, secondary, and tertiary growth forms, which are also commonly hypothesized as growth stages. The identification of these forms is primarily based on the size and folding status of the floating leaves. However, we identified 12 forms in the greenhouse and the field. Our experiments showed that the folding of floating leaves is a reversible trait dependent on water access. The floating leaves quickly fold in response to water shortage, reducing water loss and needs, decreasing growth, and avoiding trichome damage. The leaves re-open to allow trichomes repel water and enhance growth when having adequate water supply. Larger secondary or tertiary forms do not produce small-leaf primary forms without high intensity stress. These results do not support the hypothesis that three growth forms represent sequential growth stages. The abnormal small-leaf forms are the result of endocide-induced autotoxicity and some of them never grow into other forms. The development of abnormal forms and reversible leaf folding strategy in response to high stress along with rapid asexual reproduction are major adaptive traits contributing to the invasiveness of S. molesta.

Lead-Induced Physiological, Biochemical and Enzymatic Changes in Asplenium scolopendrium L.

The paper aims to determine the lead-induced physiological, biochemical and enzymatic changes in Asplenium scolopendrium, which could represent biomarkers used in environmental assessment. Of all the physiological processes, photosynthesis and respiration were analyzed and the enzymatic and biochemical determinations focused on catalase activity, assimilatory pigment concentration, polyphenol content and lead presence in tissues.The stress induced by the exposure to Pb of the species Asplenium scolopendrium determined an increase in the carotenoid content, the catalase activity, the total polyphenol content and also enhanced the respiration potential. No significant changes were recorded regarding the chlorophyll content and the photosynthetic activity. The recorded changes may be used as non-specific markers in the assessment of the impact of Pb on plants (Asplenium scolopendrium).

Salinity-induced inhibition of growth in the aquatic pteridophyte Azolla microphylla primarily involves inhibition of photosynthetic components and signaling molecules as revealed by proteome analysis.

Salinity stress causes adverse physiological and biochemical changes in the growth and productivity of a plant. Azolla, a symbiotic pteridophyte and potent candidate for biofertilizer due to its nitrogen fixation ability, shows reduced growth and nitrogen fixation during saline stress. To better understand regulatory components involved in salinity-induced physiological changes, in the present study, Azolla microphylla plants were exposed to NaCl (6.74 and 8.61 ds/m) and growth, photochemical reactions of photosynthesis, ion accumulation, and changes in cellular proteome were studied. Maximum dry weight was accumulated in control and untreated plant while a substantial decrease in dry weight was observed in the plants exposed to salinity. Exposure of the organism to different concentrations of salt in hydroponic conditions resulted in differential level of Na+ and K+ ion accumulation. Comparative analysis of salinity-induced proteome changes in A. microphylla revealed 58 salt responsive proteins which were differentially expressed during the salt exposure. Moreover, 42 % spots among differentially expressed proteins were involved in different signaling events. The identified proteins are involved in photosynthesis, energy metabolism, amino acid biosynthesis, protein synthesis, and defense. Downregulation of these key metabolic proteins appears to inhibit the growth of A. microphylla in response to salinity. Altogether, the study revealed that in Azolla, increased salinity primarily affected signaling and photosynthesis that in turn leads to reduced biomass.

Glutathione and abscisic acid supplementation influences somatic embryo maturation and hormone endogenous levels during somatic embryogenesis in Podocarpus lambertii Klotzsch ex Endl.

Here we propose a protocol for embryogenic cultures induction, proliferation and maturation for the Brazilian conifer Podocarpus lambertii, and investigated the effect of abscisic acid (ABA) and glutathione (GSH) supplementation on the maturation phase. ABA, zeatin (Z) and salicylic acid (SA) endogenous levels were quantified. Number of somatic embryos obtained in ABA-supplemented treatment was significant higher than in ABA-free treatment, showing the relevance of ABA supplementation during somatic embryos maturation. Histological analysis showed the stereotyped sequence of developmental stages in conifer somatic embryos, reaching the late torpedo-staged embryo. GSH supplementation in maturation culture medium improved the somatic embryos number and morphological features. GSH 0mM and GSH 0.1mM treatments correlated with a decreased ABA endogenous level during maturation, while GSH 0.5mM treatment showed constant levels. All treatments resulted in decreased Z endogenous levels, supporting the concept that cytokinins are important during the initial cell division but not for the later stages of embryo development. The lowest SA levels found in GSH 0.5mM treatment were coincident with early embryonic development, and this treatment resulted in the highest development of somatic embryos. Thus, a correlation between lower SA levels and improved somatic embryo formation can be hypothesized.

The influence of humic substance on Cd accumulation of phytostabilizer Athyrium wardii (Hook.) grown in Cd-contaminated soils.

The application of organic amendments into heavy metal contaminated soil is considered as an environmentally friendly technique to promote the potential of phytoremediation. A pot experiment was carried out to evaluate the effect of humic substances on growth, cadmium (Cd) accumulation and phytostabilization potential of the mining ecotype (ME) and the corresponding non-mining ecotype (NME) of Athyrium wardii (Hook.) grown in Cd-contaminated soils. The addition of the humic substances demonstrated great promotion for the growth and Cd uptake of ME. Both plant biomass and Cd concentration significantly increased with the increasing application of the humic substances up to 100 g kg(-1), beyond which no significant change of underground part biomass and Cd concentrations in underground part of A. wardii was observed. The maximum Cd concentration in underground part of ME was 180 mg kg(-1) when 150 g kg(-1) humic substances were applied. The ME showed greater Cd accumulation capability in underground part (0.47-0.68 mg plant(-1)) than that of NME (0.27-0.45 mg plant(-1)). Increasing bioaccumulation coefficient (BCF) values of A. wardii was observed with increasing application of the humic substances. The BCF values of ME were higher than those of NME. However, the use of the humic substances exhibited little impact on translocation factors (TFs) of ME, and the TF values of ME were less than NME. Furthermore, the application of the humic substances improved the remediation factors (RFs) of A. wardii. The RF values in underground part of ME ranging from 0.73 to 0.91 % were apparently higher than those of NME. These results indicated that the humic substances can be a potential candidate for enhancing the phytostabilization of A. wardii grown in Cd-contaminated soils.

The copper spoil heap Knappenberg, Austria, as a model for metal habitats - Vegetation, substrate and contamination.

Historic mining in the Eastern Alps has left us with a legacy of numerous spoil heaps hosting specific, metal tolerant vegetation. Such habitats are characterized by elevated concentrations of toxic elements but also by high irradiation, a poorly developed substrate or extreme pH of the soil. This study investigates the distribution of vascular plants, mosses and lichens on a copper spoil heap on the ore bearing Knappenberg formed by Prebichl Layers and Werfener Schist in Lower Austria. It serves as a model for discriminating between various ecological traits and their effects on vegetation. Five distinct clusters were distinguished: (1) The bare, metal rich Central Spoil Heap was only colonised by highly resistant specialists. (2) The Northern and (3) Southern Peripheries contained less copper; the contrasting vegetation was best explained by the different microclimate. (4) A forest over acidic bedrock hosted a vegetation overlapping with the periphery of the spoil heap. (5) A forest over calcareous bedrock was similar to the spoil heap with regard to pH and humus content but hosted a vegetation differing strongly to all other habitats. Among the multiple toxic elements at the spoil heap, only Cu seems to exert a crucial influence on the vegetation pattern. Besides metal concentrations, irradiation, humidity, humus, pH and grain size distribution are important for the establishment of a metal tolerant vegetation. The difference between the species poor Northern and the diverse Southern Periphery can be explained by the microclimate rather than by the substrate. All plant species penetrating from the forest into the periphery of the spoil heap originate from the acidic but not from the calcareous bedrock.