Toxic effects of Pb2+ on the growth and mineral nutrition of signal grass (Brachiaria decumbens) and Rhodes grass (Chloris gayana)

Although grasses are commonly used to revegetate sites contaminated with lead (Pb), little is known regarding the Pb-tolerance of many of these species. Using dilute solution culture to mimic the soil solution, the growth of signal grass (Brachiaria decumbens Stapf cv. Basilisk) and Rhodes grass (Chloris gayana Kunth cv. Pioneer) was related to the mean activity of Pb²⁺ {Pb²⁺} in solution. There was a 50% reduction in fresh mass of signal grass shoots at 5 μM {Pb²⁺} and at 3 μM {Pb²⁺} for the roots. Rhodes grass was considerably more sensitive to Pb in solution, with shoot and root fresh mass being reduced by 50% at 0.5 μM {Pb²⁺}. The higher tolerance of signal grass to Pb appeared to result from the internal detoxification of Pb, rather than from the exclusion of Pb from the root. At toxic {Pb²⁺}, an interveinal chlorosis developed in the shoots of signal grass (possibly a Pb-induced Mn deficiency), whilst in Rhodes grass, Pb²⁺ caused a bending of the root tips and the formation of a swelling immediately behind some of the root apices. Root hair growth did not appear to be reduced by Pb²⁺ in solution, being prolific at all {Pb²⁺} in both species.     

Effects of Combined Abiotic Stresses on Growth,Trace Element Accumulation,and Phytohormone Regulation in Two Halophytic Species

Trace element contamination of lands is a serious environmental problem that limits yield and threatens human health. To study the combined effect of high salinity and toxic levels of trace elements on halophytes, the performance of two marsh species, Atriplex halimus and Suaeda fruticosa, grown for 1 month with an irrigation solution supplemented with 200 mM NaCl and 400 μM Cd²⁺ or 400 μM Cu²⁺ was evaluated. The effect of the combined stress conditions on hormone signaling was also assessed. Biomass production and chlorophyll content decreased under Cd²⁺ stress in both species, whereas Cu²⁺ had a lower impact on plant performance. The different plant sensibilities to the two trace elements assayed indicate that each metal has a different effect on plants. Furthermore, the deleterious effect of metal toxicity was alleviated when NaCl was added to the irrigation solution, demonstrating that NaCl improves plant performance and tolerance of halophytic species to cope with trace element intoxication. Results show that both species accumulated important quantities of Cd²⁺ and Cu²⁺ in roots (Cd²⁺: 2,690–3,130 μg g^?1 DW and Cu²⁺: 2,070–2,770 μg g^?1 DW); this finding allows us to classify these species among the hyperaccumulator plants. Cd²⁺ and Cu²⁺ differently affected endogenous phytohormone contents in both species. Data suggest an essential involvement of roots on the regulation of tolerance to trace elements. Therefore, indole-3-acetic acid levels increased in roots of both species irrigated with high levels of Cd²⁺, which suggests that the auxin may stimulate root promotion and growth under these stress conditions. Other compounds, classically considered as “stress hormones” showed very different patterns of accumulation. Whereas, salicylic acid (SA) levels in roots and leaves increased in response to Cd²⁺, root contents of jasmonic acid (JA), and abscisic acid (ABA) decreased. In leaves, the rambling pattern of accumulation observed for JA and ABA suggested the lack of a specific role in regulation against trace element toxicity. Together, data suggest that SA could act as a specific signal that detects trace element toxicity, whereas JA and ABA promote general responses against abiotic stress.     

Effect of larch (Larix gmelini Rupr.) root exudates on Manchurian walnut (Juglans mandshurica Maxim.) growth and soil juglone in a mixed-species plantation

The establishment and productivity of a Manchurian walnut (Juglans mandshurica Maxim.) plantation can be improved by inter-planting with larch (Larix gmelini Rupr.) in Northeast China, but the potential mechanism remains obscure. We carried out a series of experiments in a 20-year-old mixed-species plantation, as well as in Manchurian walnut and larch plantations. Manchurian walnut seedlings had difficulty surviving in the Manchurian walnut plantation because their growth was inhibited by their own soil and root exudates. In sharp contrast, Manchurian walnut seedlings grew well in larch and mixed-species plantations. Larch soil and root exudates greatly stimulated the growth of Manchurian walnut seedlings in controlled conditions. In particular, larch root exudates can increase the soil microbial populations, including bacteria, actinomycetes, azotobacter and cellulose-decomposing microorganisms; larch root exudates can also increase the enzyme activities of saccharase, urease, proteinase and polyphenol oxidase. Significant results led to a rapid degradation of the root-exuded phytotoxic juglone from Manchurian walnut. Manchurian walnut root exudates contained juglone at a high concentration of 121.3?±?6.6 mg g^?1, while juglone concentrations in the soil beneath Manchurian walnut trees ranged from 2.9–6.2 µg g^?1 soil. It appears from the results that juglone may be released from Manchurian walnut roots into the soil in a sufficient quantity but rapidly degrades due to interactions with soil factors. Furthermore, juglone was more resistant toward degradation in the Manchurian walnut soil (t _1/2 ?=?7.36?±?0.63 h) when compared to the larch soil (t _1/2 ?=?4.66?±?0.82 h). The results suggest that larch may improve the establishment and productivity of Manchurian walnut in a mixed-species plantation through the release of root exudates.     

Variation in seedling growth of 11 perennial legumes in response to phosphorus supply

Phosphorus (P) deficiency is a major problem for Australian agriculture. Development of new perennial pasture legumes that acquire or use P more efficiently than the current major perennial pasture legume, lucerne (Medicago sativa L.), is urgent. A glasshouse experiment compared the response of ten perennial herbaceous legume species to a series of P supplies ranging from 0 to 384 µg g^?1 soil, with lucerne as the control. Under low-P conditions, several legumes produced more biomass than lucerne. Four species (Lotononis bainesii Baker, Kennedia prorepens F.Muell, K. prostrata R.Br, Bituminaria bituminosa (L.) C.H.Stirt) achieved maximum growth at 12 µg P g^?1 soil, while other species required 24 µg P g^?1. In most tested legumes, biomass production was reduced when P supply was ≥192 µg g^?1, due to P toxicity, while L. bainesii and K. prorepens showed reduced biomass when P was ≥24 µg g^?1 and K. prostrata at ≥48 µg P g^?1 soil. B. bituminosa and Glycine canescens F.J.Herm required less soil P to achieve 0.5 g dry mass than the other species did. Lucerne performed poorly with low P supply and our results suggest that some novel perennial legumes may perform better on low-P soils.     

The effect of zinc on the growth and physiological and biochemical parameters in seedlings of Eruca sativa (L.) (Rocket)

Eruca sativa seedlings were treated with different Zn concentrations (0, 250, 500, 1,000, 2,000 μg g^?1 dried growth medium) under controlled conditions. The seedlings were harvested 20 days after Zn treatment. Physiological parameters, such as root and shoot length, fresh and dry weight, were measured and Zn content of roots and shoots was determined. Furthermore, various biochemical parameters were studied on E. sativa leaves: enzymatic antioxidants, such as superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX), and non-enzymatic antioxidants, such as ascorbate, non-protein thiols. Malondialdehyde, which is an index of lipid peroxidation, was assayed. Zn treatment did not have any significant effect on fresh and dry weights, whereas 500 μg g^?1 Zn increased root growth significantly (p < 0.05). Zn accumulated in roots 2–8 times more than it did in leaves. Lipid peroxidation increased in proportion with the increase in Zn. Although a decrease in SOD and CAT activities at increased Zn was found, a significant increase in APX and POD was observed at 500 and 1,000 μg g^?1 Zn, respectively. In addition, an increase in the amounts of non-protein thiols and total AsA (Ascorbate) was observed with the increase in Zn.     

Boron induced changes in biochemical constituents,enzymatic activities,and growth performance of wheat

The present study investigates how excess boron (B) affects and alters the biochemical constituents and enzymatic activities of wheat (Triticum aestivum var. ‘Raj 4037’), consequently leading to reduced plant growth and yield. Plants were raised in soils supplemented with various concentrations of B (0, 1, 2, 4, 8, 16, and 32 µg B g^?1 soil). Biochemical constituents including soluble leaf protein contents, total phenol contents, soluble sugar contents, proline contents, enzymatic activities of peroxidase (POX), and nitrate reductase (NR) were analyzed. In addition, growth parameters namely shoot–root length, shoot–root fresh and dry weight, seed number and seed weight were analyzed to assess the impact of B toxicity. Results indicate that change in biochemical constituents were correlated with B treatments. Boron concentrations beyond 4 µg g^?1 significantly increased soluble leaf protein contents, total phenol contents, soluble sugar contents, and proline contents. The POX activity was found to be positively correlated with B treatments. B significantly affects nitrogen metabolism and nitrate accumulation which is reflected by the downregulation of NR activity at higher B concentrations. B induced changes in physiological parameters of the plant which subsequently led to the reduction in growth, biomass production, and yield attributes. Out of the various concentrations of B, 8 µg g^?1 was moderately toxic while 16 and 32 µg g^?1 generated high toxicity and induced B stress response to confer tolerance in wheat. Further, a possible mechanism of B toxicity response in wheat is suggested.     

Soil N and C trace gas fluxes and microbial soil N turnover in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary

During two intensive field campaigns in summer and autumn 2004 nitrogen (N₂O, NO/NO₂) and carbon (CO₂, CH₄) trace gas exchange between soil and the atmosphere was measured in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N₂O emission rates were 1.5 μg N m⁻² h⁻¹ in summer and 3.4 μg N m⁻² h⁻¹ in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 μg N m⁻² h⁻¹) as compared to summer (6.0 μg N m⁻² h⁻¹). However, as NO₂ deposition rates continuously exceeded NO emission rates (−9.7 μg N m⁻² h⁻¹ in summer and −18.3 μg N m⁻² h⁻¹ in autumn), the forest soil always acted as a net NO _x sink. The mean value of CO₂ fluxes showed only little seasonal differences between summer (81.1 mg C m⁻² h⁻¹) and autumn (74.2 mg C m⁻² h⁻¹) measurements, likewise CH₄uptake (summer: −52.6 μg C m⁻² h⁻¹; autumn: −56.5 μg C m⁻² h⁻¹). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N₂O/CH₄ soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO_{2 resp} ΔO_{2 resp}⁻¹) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 μg N kg⁻¹ SDW d⁻¹) and autumn measurements (0.89 μg N kg⁻¹ SDW d⁻¹). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 μg N kg⁻¹ SDW d⁻¹) and significantly lower in the uppermost mineral layer (1.3–2.9 μg N kg⁻¹ SDW d⁻¹). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N₂O emissions and negatively correlated with CH₄ uptake, whereas soil CO₂ emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn.     

Elicitor mediated enhancement of wedelolactone in cell suspension culture of <Emphasis Type="Italic">Eclipta alba</Emphasis> (L.) Hassk

The present research focused on enhancing the production of wedelolactone through cell suspension culture (CSC) in Eclipta alba (L.) Hassk. With an aim of attaining a sustainable CSC, various plant growth regulators, elicitors and agitation speed were examined. Nodal segments of in vitro propagated plantlets induced the maximum percentage (93.47?±?0.61%) of callus inoculated on Murashige and Skoog (MS) medium fortified with picloram (2 mg L^?1). The growth kinetics of CSC exhibited a sigmoid pattern with a lag phase (0–6 days), a log phase (6–18 days), a stationary phase (18–24 days) and then death phase thereafter. The highest biomass accumulation in CSC with 7.09?±?0.06 g 50 mL^?1 fresh weight, 1.52?±?0.02 g 50 mL^?1 dry cell weight, 1.34?±?0.01?×?10⁶ cell mL^?1 total cell count and 57.00?±?0.58% packed cell volume was obtained in the liquid MS medium supplemented with 1.5 mg L^?1 picloram plus 0.5 mg L^?1 kinetin at 120 rpm. High performance thin layer chromatography confirmed that yeast extract (biotic elicitor) at 150 mg L^?1 accumulated more CSC biomass with 1.22-fold increase in wedelolactone (288.97?±?1.94 µg g^?1 dry weight) content in comparison to the non-elicited CSC (237.78?±?0.04 µg g^?1 dry weight) after 120 h of incubation. Contrastingly, methyl jasmonate (abiotic elicitor) did not alter the biomass but increased the wedelolactone content (259.32?±?1.06 µg g^?1 dry weight) to an extent of 1.09-fold at 100 µM. Complete plantlet regeneration from CSC was possible on MS medium containing N⁶-benzyladenine (0.75 mg L^?1) and abscisic acid (0.5 mg L^?1). Thus, the establishment of protocol for CSC constitutes the bases for future biotechnological improvement studies in this crop.     

Salicylic acid accumulation as a result of Cu,Zn, Cd and Pb interactions in common reed (<Emphasis Type="Italic">Phragmites australis</Emphasis>) growing in natural ecosystems

Common reed (Phragmites australis (Cav.) Trin. ex Steud.) plants were harvested from four natural water ecosystems of the Bogdanka river catchment (Poznań, Poland) four times throughout the 2014 vegetative season. Over the year, average metal contents followed different decreasing trends according to the analyzed tissue: Zn > Cu ≈ Pb > Cd (rhizomes) and Zn > Pb > Cu > Cd (leaves), and mean translocation ratios (leaves/rhizomes) were found as follows: 0.93, 0.70, 0.65, 0.40 for Zn, Pb, Cd and Cu, respectively. Metal content increased gradually during the growing season, and in the case of Cu, Cd and Pb exceeded the upper limit of average concentration detected in plants from natural ecosystems. However, the content of salicylic acid did not follow the increase of metal accumulation. In rhizomes, the highest production of the metabolite was observed in May and reached 324 ng g^?1 fresh weight (FW) (mean value). Afterwards, a significant drop to 50 ng g^?1 FW was observed. Simultaneously, the highest values of total salicylic acid in P. australis leaves were observed in July and accompanied the intensive development of the aboveground biomass of the plant (11.3 µg g^?1 FW–mean value). Subsequently, its content in leaves showed a significant decrease down to 2.1 µg g^?1 FW in November. Multivariate regression analysis revealed significant interactions between analyzed metals influencing the plant response to metal-derived stress. Cu and Zn showed antagonistic properties considering their uptake and the induction of salicylic acid biosynthesis, whereas non-essential metals (Pb and Cd) acted similarly and stimulated the formation of salicylic acid glucoside.     

Temporal variability of solution Cd2+ concentration in metal-contaminated soils as affected by soil temperature: consequences on lettuce (Lactuca sativa L.) exposure

The aim of this study was to assess how the solubility and the speciation of Cd in soil solution were affected over time by the soil temperature for three metal-contaminated soils. The changes of solution Cd concentration (either total or free ionic) and other physico-chemical parameters (e.g. pH, ionic strength, the concentrations of ${\text{NO}}_3^ - $ , ${\text{SO}}_4^{2 - } $ , Ca, Mg and dissolved organic carbon) were monitored over a 28-day culture of lettuce (Lactuca sativa L.) in soils incubated at 10°C, 20°C or 30°C. The major result of this study was that Cd²⁺ concentration greatly varied over time in soil solution. The Cd²⁺ concentration declined over time in soil solution as did the concentration of cations that may compete for adsorption (Ca²⁺, Mg²⁺). The rise in soil temperature primarily impacted on the concentration of Cd²⁺ via promoting the microbial C-degradation and, thus, the complexation of Cd in soil solution. The integration of the temporal variations in Cd²⁺ concentration through the calculation of the root exposure to solution Cd (E _Cd) provided a fairly close and robust prediction of Cd concentration in lettuce roots. The present work thus provided new insights on the fate of Cd in contaminated soils that may be relevant for predicting the root uptake of Cd.     

In vitro tetraploidization for the augmentation of wedelolactone in <Emphasis Type="Italic">Sphagneticola calendulacea</Emphasis> (L.) Pruski

A practical and reliable method for in vitro tetraploidization of Sphagneticola calendulacea (L.) Pruski [synonym Wedelia chinensis (Osbeck) Merrill] has been established to enhance the production of wedelolactone. Shoot tip and nodal explants from in vitro-grown culture (2n?=?50) were exposed to the antimitotic chemical, i.e., colchicine, at various concentrations (0, 0.025, 0.05, 0.1, 0.3, and 0.5%; w/v) for 12, 24, 36, 48, and 60 h. The treated explants were then incubated and proliferated on Murashige and Skoog (MS) medium fortified with 0.2 mg l^?1 thidiazuron and 0.05 mg l^?1 naphthalene acetic acid, followed by root induction in 1.0 mg l^?1 indole-3 acetic acid enriched ½MS medium. Treatment of shoot tips with 0.05% colchicine for 24 h supported the maximum rate of survival (63.33%) of explants as well as tetraploid induction (42.93%). Morphological, stomatal, and cytological characteristics along with the secondary metabolite content of the in vitro tetraploids were compared to that of diploids. The recovered tetraploid plants possessed superior plant height, stem diameter, leaf size, root number, and increased length and width of stomata but decreased stomatal frequency. The tetraploid plants demonstrated twice the chromosome number (2n?=?4x?=?100) than the diploids as confirmed through cytology, spectrophotometry and flow cytometry. High-performance thin-layer chromatography showed a significant enhancement in the wedelolactone content of tetraploid plants (541.48 µg g^?1 of dried sample) in comparison to diploid plants (325.43 µg g^?1 of dried sample), signifying the prospective of this technique for the trade value improvement.     

Optimization and quality assessment of adventitious roots culture in Panax quinquefolium L.

In this study, adventitious roots of Panax quinquefolium L. have been successfully established. The highest induction rate of roots was obtained in MS medium containing 3 mg L^?1 IBA after 4 weeks of culture. The culture conditions of adventitious root were optimized and evaluated with response surface methodology. The best culture conditions for root growth seemed to be 0.75 salt strength MS medium, 4.70 g L^?1 inoculum size and 40 days of culture. The active component contents of adventitious roots were compared with those of native roots. The total saponins content was found to be 16.28 mg g^?1 in native root and 4.64 mg g^?1 in adventitious root. The polysaccharide content of the adventitious root was 1.5 times higher than that in the native P. quinquefolium (30.54 vs. 20.28 mg g^?1).     

Production of biomass and bioactive compounds by adventitious root suspension cultures of Morinda citrifolia (L.) in a liquid-phase airlift balloon-type bioreactor

To improve root growth and production of bioactive compounds such as anthraquinones (AQ), phenolics, and flavonoids by adventitious root cultures of Morinda citrifolia, the effects of aeration rate, inoculum density, and Murashige and Skoog (MS) medium salt strengths were investigated using a balloon-type bubble bioreactor. The possible mechanisms underlying changes in activities of enzymic (superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase) and nonenzymic (vitamin E) antioxidants, phenylalanine ammonia lyase, and stress levels (accumulation of hydrogen peroxide and proline, peroxidation of lipids) were also studied. Low aeration rate (0.05 vvm [air volume/culture volume/min]) accelerated accumulation of root fresh weight and dry weight (DW). High aeration rates (0.1 to 0.3 vvm) stimulated accumulation of AQ, phenolics, and flavonoids and reduced root growth. Low inoculum densities (5 and 10 g l^–1) increased accumulation of those metabolites but inhibited root growth. Culture of adventitious roots with high concentrations of MS salts (1× and 1.5× MS) resulted in induction of oxidative stress that strongly inhibited root growth. Overall, an aeration rate of 0.05 vvm, 15 g l^–1 inoculum density, and half-strength (0.5×) MS medium were optimal for enhancing accumulation of root dry biomass (4.38 g l^–1), AQ (103.08 mg g^–1 DW), phenolics (54.81 mg g^–1 DW), and flavonoids (49.27 mg g^–1 DW).     

Cadmium effects and accumulation in cultures ofProrocentrum micans (dinophyta)

Effects and accumulation of cadmium were studied in unialgal 10-1 batch-culture experiments with the dinoflagellateProrocentrum micans Ehrenberg. Tests were made using sterile filtered North Sea water enriched with nitrate and phosphate only in order to avoid disturbances by complex formation. Cadmium was added to the cultures in amounts of 100 to 0.13μg l⁻¹. In one series it was added at the start of the experiments and in a second one after a growth period of 1 week. Addition of only 1.2μg Cd l⁻¹ reduces multiplication rates and maximum cell densities of the algae. Not until 0.4μg Cd⁻¹ does growth correspond to that of the controls. Cadmium concentrations were measured, after filtration, in the culture medium and in the biomass by means of flameless AAS. The cadmium content in algae increased from 2.7μg g⁻¹ (dry weight) in controls to 500μg g⁻¹ (dry weight) in media containing 100μg Cd l⁻¹. Uptake occurred rapidly during the first few days of the experiments, slowed down somewhat during exponential growth stage, and increased during decay of the cultures. Cadmium content of culture media remained nearly constant (Series 1) or decreased only slowly during experimental time (Series 2). The highest concentration factor was measured in the controls. It decreased with increasing metal concentration in the medium and increased with experimental time. Structural modifications of the cells were visible after Lugol fixation only, indicating brittleness of the cell walls.P. micans has shown to be extremely sensitive to cadmium and to accumulate this metal.     

Increased production of plumbagin in <Emphasis Type="Italic">Plumbago indica</Emphasis> root cultures by biotic and abiotic elicitors

Objectives

To evaluate the effects of 12 biotic and abiotic elicitors for increasing the production of plumbagin in Plumbago indica root cultures.

Results

Most elicitors showed minimal effects on the root dry weight, except for 250 mg chitosan l^?1 and 10 mM l-alanine that markedly decreased root biomass by about 40 % compared to the untreated root cultures (5 g l^?1). Treatments with 100 µM AgNO₃ significantly increased intracellular plumbagin production by up to 7.6 mg g^?1 DW that was 4-fold more than the untreated root cultures (1.9 mg g^?1 DW). In contrast, treatments with 150 mg chitosan l^?1, 5 mM l-alanine, and 50 µM 1-naphthol significantly enhanced the extracellular secretion of plumbagin by up to 10.6, 6.9, and 5.7 mg g^?1 DW, respectively, and increased the overall production of plumbagin by up to 12.5, 12.5, and 9.4 mg g^?1 DW, respectively.

Conclusions

Chitosan (150 mg l^?1), l-alanine (5 mM), and 1-naphthol (50 µM) were the best elicitors to enhance plumbagin production in P. indica root cultures.

     

Differential competence for in vitro adventitous rooting of grass pea (Lathyrus sativus L.)

Grass pea (Lathyrus sativus L.) family leguminosae is cultivated as an important food and feed crop all over the world. It is very recalcitrant and difficult to regenerate and root under in vitro conditions. In this cotext, the study was carried out in three steps to find out the effects of three auxins [naphthalene acetic acid, indole 3 butyric acid, indole-3-acetic acid (IAA)], four sucrose concentrations and six types of substrate most suited for plant growth and helpful in acclimatisation of grass pea. The results showed that 2 mg L^?1 IAA, 3 % sucrose was most suitable for rooting of grass pea. When different concentrations of sucrose were supplied to optimum concentration of IAA in Murashige and Skoog medium, 4.5 % sucrose concentration induced maximum number of 13.70 roots per explants that had positive impact on root length, fresh and dry weight of roots, plant height and morphology of the growing plants. There was 92.66 % acclimatisation and survival rate of these plants using peat moss compared to five other substrates used in this study. The developing plants were vigorous, flowered and set seed contained in pods under glass house conditions. It is concluded that rooting is affected by type and concentration of plant growth regulators and type of substrate has direct bearing on acclimatisation, flowering, pod and seed set of grass pea. As such this paper reports an efficient rooting and acclimatisation system of grass pea that will be very useful in future genetic transformation and breeding for improved characteristics.     

Significant enhancement of lignan accumulation in hairy root cultures of Linum album using biotic elicitors

Linum album has been shown to accumulate some lignans with antiviral and anticancer properties such as podophyllotoxin (PTOX) and 6-methoxy podophyllotoxin (MPTOX). In this research, we examined the effects of fungal elicitors on the production of lignans in L. album hairy root cultures. The biosynthesis of lignans was differentially affected by fungal elicitors. Fusarium graminearum extract induced the highest increase of PTOX, 190 μg g^?1 dry weight (DW), and lariciresinol, 260 μg g^?1 DW, which was two-fold and three-fold greater than the untreated control, respectively, while Trichoderma viride extract enhanced the accumulation of MPTOX, instead of PTOX, up to 160 µg g^?1 DW, which was 2.4-fold greater than the control. The enhancing effects of fungal elicitors on lignans production was correlated with the increased expression of some key genes involved in the biosynthesis of these compounds, phenylalanine ammonia-lyase, cinnamoyl-CoA reductase, cinnamyl-alcohol dehydrogenase and pinoresinol-lariciresinol reductase.     

Dust mediated transfer of phosphorus to alpine lake ecosystems of the Wind River Range,Wyoming, USA

Alpine lakes receive a large fraction of their nutrients from atmospheric sources and are consequently sensitive to variations in both the amount and chemistry of atmospheric deposition. In this study we explored the spatial changes in lake water chemistry and biology along a gradient of dust deposition in the Wind River Range, Wyoming. Regional differences were explored using the variation in bulk deposition, lake water, sediment, and bedrock geochemistry and catchment characteristics. Dust deposition rates in the Southwestern region averaged 3.34 g m^?2 year^?1, approximately three times higher than deposition rates in the Northwestern region (average 1.06 g m^?2 year^?1). Dust-P deposition rates ranged from 87 µg P m² day^?1 in the Northwestern region to 276 µg P m² day^?1 in the Southwestern region. Subalpine and alpine lakes in the Southwestern region had greater total phosphorus (TP) concentrations (5–13 µg L^?1) and greater sediment phosphorus (SP) concentrations (2–5 mg g^?1) than similar lakes elsewhere in the region (1–8 µg L^?1 TP, 0.5–2 mg g^?1 SP). Lake phosphorus concentrations were related to dissolved organic carbon (DOC) across vegetation gradients, but related to the percent of bare rock, catchment area to lake area, and catchment steepness across dust deposition gradients. Modern phytoplankton and zooplankton biomasses were two orders of magnitude greater in the Southwest than in the Northwest, and alpine lakes in the Southwest had a unique diatom species assemblage with relatively higher concentrations of Asterionella formosa, Pseudostaurosira pseudoconstruens, and Pseudostaurosira brevistriata. These results suggests that catchment controls on P export to lakes (i.e. DOC) are overridden in dominantly bare rock basins where poor soils cannot effectively retain dust deposited P.     

Cadmium Removal Potential from Contaminated Soil by Tagetes erecta L. and Panicum maximum: Influence of Soil pH

The potential for cadmium (Cd) removal from contaminated soil by two species—marigold (Tagetes erecta L.) and Guinea grass (Panicum maximum)—was investigated in pot culture experiments in a greenhouse in triplicate. The concentration of Cd was varied from 50 to 200 mg kg^?1 and the pH was varied from 5.0 to 7.5 to investigate the effect of pH on Cd uptake. The results showed that total biomass of Guinea grass was around nine and seven times higher than that of marigold for Cd treatments of 50 and 100 mg kg^?1 at pH 5.0, respectively. Total cadmium uptake at Cd treatments of 50 and 100 mg kg^?1 at pH 5.0 by Guinea grass was 19.28 ± 3.14 and 36.06 ± 4.28 mg kg^?1, respectively, and for marigold was 15.66 ± 4.17 and 20.38 ± 3.24 mg kg^?1, respectively. The total Cd uptake by Guinea grass was 1.23 and 1.77 higher than that of marigold at Cd treatments of 50 and 100 mg kg^?1, respectively, at pH 5.0 due to higher biomass. The maximum Cd uptake by marigold and Guinea grass occurred at pH 5.0 at Cd treatment of 100 mg kg^?1. The results clearly show that the two species behave very differently for Cd uptake. Guinea grass is easy to grow, drought tolerant and, due to its higher biomass, it can be used for remediation of Cd-contaminated soil.     

Elevated CO2 improves root growth and cadmium accumulation in the hyperaccumulator Sedum alfredii

Aims

This study examined the effect of elevated CO₂ on plant growth, root morphology and Cd accumulation in S. alfredii, and assessed the possibility of using elevated CO₂ as fertilizer to enhance phytoremediation efficiency of Cd-contaminated soil by S. alfredii.

Methods

Both soil pot culture and hydroponic experiments were carried out to characterize plant biomass, root morphological parameters, and cadmium uptake in S. alfredii grown under ambient (350 μL L^?1) or elevated (800 μL L^?1) CO₂.

Results

Elevated CO₂ prompted the growth of S. alfredii, shoot and root biomass were increased by 24.6–36.7% and 35.0–52.1%, respectively, as compared with plants grown in ambient CO₂. After 10 days growth in medium containing 50 μM Cd under elevated CO₂, the development of lateral roots and root hairs were stimulated, additionally, root length, surface area, root volume and tip number were increased significantly, especially for the finest diameter roots. The total Cd uptake per pot was significantly greater under elevated CO₂ than under ambient CO₂. After 60 d growth, Cd phytoextraction efficiency was increased significantly in the elevated CO₂ treatment.

Conclusions

Results suggested that the use of elevated CO₂ may be a useful way to improve phytoremediation efficiency of Cd-contaminated soil by S. alfredii.