Arsenic Uptake by Lemna minor in Hydroponic System

Arsenic is hazardous and causes several ill effects on human beings. Phytoremediation is the use of aquatic plants for the removal of toxic pollutants from external media. In the present research work, the removal efficiency as well as the arsenic uptake capacity of duckweed Lemna minor has been studied. Arsenic concentration in water samples and plant biomass were determined by AAS. The relative growth factor of Lemna minor was determined. The duckweed had potential to remove as well as uptake arsenic from the aqueous medium. Maximum removal of more than 70% arsenic was achieved at initial concentration of 0.5 mg/l arsenic on 15th day of experimental period of 22 days. Removal percentage was found to decrease with the increase in initial concentration. From BCF value, Lemna minor was found to be a hyperaccumulator of arsenic at initial concentration of 0.5 mg/L, such that accumulation decreased with increase in initial arsenic concentration.     

Removal of fluoride contamination in water by three aquatic plants

Phytoremediation, popularly known as ‘green technology’ has been employed in the present investigation to examine the potential of fluoride removal from water by some aquatic plants. Fluoride contamination in drinking water is very much prevalent in different parts of the world including India. Batch studies were conducted using some aquatic plants e.g., Pistia stratiotes, Eichhornia crassipes, and Spirodela polyrhiza which profusely grow in natural water bodies. The experimental data exhibited that all the above three aquatic floating macrophytes could remove fluoride to some relative degree of efficiency corresponding to initial concentration of fluoride 3, 5, 10, 20 mg/l after 10 days exposure time. Result showed that at lower concentration level i.e., 3 mg/L removal efficiency of Pistia stratiotes (19.87%) and Spirodela polyrhiza (19.23%) was found to be better as compared to Eichhornia crassipes (12.71%). Some of the physiological stress induced parameters such as chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, total protein, catalase, and peroxidase were also studied to explore relative damage within the cell. A marginal stress was imparted among all the plants for lower concentration values (3 mg/L), whereas at 20 mg/l, maximum damage was observed.     

Cadmium-induced responses in duckweed <Emphasis Type="Italic">Lemna minor</Emphasis> L.

Although duckweed Lemna minor L. is a known accumulator of cadmium, detailed studies on its physiological and/or defense responses to this metal are still lacking. In this study, the effects of 10 μM CdCl₂ on Lemna minor were monitored after 6 and 12 days of treatment, while growth was estimated every 2 days. Cadmium treatment resulted in progressive accumulation of the metal in the plants and led to a decrease in the growth rate to 54% of the control value. The metal also considerably impaired chloroplast ultrastructure and caused a significant reduction in pigment content, i.e., at day 12, by 30 and 34% for chlorophylls a and b, and by 25% for carotenoids. During cadmium treatment, the contents of malondialdehyde and endogenous H₂O₂ progressively increased (rising 77 and 46% above the controls by day 12), indicating that cadmium induced considerable oxidative stress. On the other hand, higher activities of pyrogallol peroxidase (PPX), ascorbate peroxidase (APX) and catalase (CAT), as well as the induction of a new APX isoform, in cadmium-treated plants, clearly showed activation of an antioxidative response. At day 6, only PPX activity was significantly above the controls (15%), while, at day 12, PPX, APX and CAT activities were increased (74, 78 and 63%). Cadmium also led to accumulation of the heat shock protein 70 (HSP70) and induced an additional isoform of this protein. The obtained results suggest that cadmium (10 μM) is phytotoxic to Lemna minor, inducing oxidative stress, and that antioxidative enzymes and HSP70 play important roles in the defense against cadmium toxicity. M. Tkalec and T. Prebeg contributed equally to this work     

Isotherm and kinetic modelling of Toluidine Blue (TB) removal from aqueous solution using Lemna minor

The aim of this study was to investigate the ability of Lemna minor for Toluidine Blue (TB) removal. Influence of the initial concentration over the removal process was considered. Experimental data have been analyzed using Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Elovich isotherm models. In addition, several kinetic models, pseudo-first-, pseudo-second-order, intraparticle and film diffusion models were considered. Langmuir and Freundlich isotherm suggested a favorable adsorption of TB by Lemna minor plants. From the D–R the mean free energy was calculated to be 11.18 kJ/mol, which indicates that TB adsorption was characterized by a chemisorption process. Kinetic studies showed that liquid film diffusion plays an important role during the process. Adsorption capacities of up to 26.69 mg/g and a high capacity of adaptation indicated that phytoremediation using Lemna minor could be a valuable alternative for dyes removal from wastewaters.     

The effect of Stratiotes aloides L. and nutrients on the growth rate of Lemna minor L.

We tried to find the reasons for frequently observed low biomass of Lemna minor among floating rosettes of Stratiotes aloides as opposed to the abundance of Spirodela polyrhiza in these stands. The effect of S. aloides on L. minor was analysed in outdoor culture experiments. The duckweed collected from among dense stands of the floating form of S. aloides (test sites) showed a significantly lower growth rate than that from stands free of the water soldier (control sites). Water from the latter stands was significantly richer in nitrate-nitrogen and ammonium-nitrogen, but not in soluble reactive phosphorus suggesting possible nutrient depletion as a reason for observed differences. Growth rates of L. minor were indeed significantly correlated with in situ concentrations of all dissolved nutrients and showed saturation at around 0.18 mg N-NH₄ dm⁻³ and 0.05 mg SRP dm⁻³ above which the growth rates did not increase significantly. We used stepwise regression to test the combined effect of nutrients and the presence/absence of S. aloides on the growth rate of L. minor. The regression showed a negligible effect of ammonium ions and nitrates on the growth rate of the duckweed. At low concentrations of soluble reactive phosphorus the presence of both the S. aloides and SRP concentrations significantly affected the growth of L. minor. Above saturating SRP concentrations none of the two effects was significant. Results of our experiments seem to suggest that the presence of S. aloides exerts a negative effect on the growth of L. minor only at low concentrations of soluble phosphorus. Since the depletion of nutrients in water by the floating form of S. aloides is unlikely, we point to S. polyrhiza as a superior competitor for nutrients and suggest a possible allelopathic effect of the water soldier on L. minor.     

Oxygen regime in a fishpond with duckweeds (lemnaceae) and Ceratophyllum

The depth of oxygen and the daily changes in oxygen concentration were assessed by in situ measurements in stands of (1) Lemnaceae; (2) Ceratophyllum; (3) Lemnaceae + Ceratophyllum; and (4) phytoplankton at the peak of the vegetation season. With the aim of excluding the influence of phytoplankton on the diurnal oxygen course, oxygen concentrations were measured in near-natural conditions below both the dense and the loose covers of Lemnaceae, placed in nutrient solution. The duckweeds Lemna minor L. and Spirodela polyrhiza (L.) Schleid. did not release any oxygen into the nutrient solution, despite the fact that their biomass increased by 7 and 4 gm^?2 dry matter per 12 h in the loose and the dense stand, respectively. The oxygen uptake by the bottom sediments reduced the oxygen concentration by up to 2 mg1^?1.     

Short term exposure of Lemna minor and Lemna gibba to mercury, cadmium and chromium

The effects of mercury (Hg), cadmium (Cd) and chromium (Cr) in concentrations ranging from 0.02 to 20 mg L^?1 applied for 24 h were assessed in Lemna minor and Lemna gibba by measuring changes in protein concentration, ascorbic acid, phenolics, malondialdehyde (MDA), hydrogen peroxide (H₂O₂), the activity of guaiacol peroxidase (G-POX) and catalase (CAT). Ascorbic acid, phenolics, catalase and guaiacol peroxidase played a key role in the antioxidative response of L. gibba. Inadequate activity of antioxidant enzymes in the L. minor resulted in MDA and H₂O₂ accumulation. In both used species, Hg treatment decreased protein content and increased CAT and G-POX activity, but decreased MDA and H₂O₂ levels. Cadmium and chromium had opposite impacts on two used Lemna species on almost all observed parameters. Enhanced antioxidative responses of L. gibba to lower concentrations of Hg, Cd and Cr indicated greater abiotic stress tolerance than L. minor.     

Allozymic and morphometric variation inLemna minor (Lemnaceae)

Allozymic and morphometric variation was studied in 28 clones ofLemna minor. This variation was compared with the corresponding variation in four clones ofLemna gibba and four clones ofSpirodela polyrrhiza. A high level of allozymic variation was observed among the clones, despite having been grown under uniform laboratory conditions for several years and despite its quasi-exclusive clonal means of propagation. Based on degree of allozymic similarity,Spirodela polyrrhiza was distinguished from the twoLemna species but the latter species were genetically indistinguishable. Allozymic similarity among clones ofLemna minor was not related to morphometric similarity, nor was it related to the degree of geographic separation or climatic similarity of their sites of origin. The results suggest that allozymic variation among these clones ofLemna minor may be largely neutral and not a consequence of differential selection.     

Host specificity and biology of the weevilNeohydronomus affinis [Coleoptera: Curculionidae] a biological control agent ofPistia stratiotes

Waterlettuce,Pistia stratiotes L., has been successfully controlled in Australia with the weevil,Neohydronomus affinis Hustache. In this study, the weevil was tested in quarantine against 34 plant species in 27 families. In non-replicated no-choice tests, it fed and oviposited on 3 species of duckweeds [(Lemna minor L.,Spirodela punctata (Meyer) Thomps.,S. polyrhiza (L.) Schleid.], frogbit [(Limnobium spongia (Bosc.) Steud.], mosquitofern (Azolla caroliniana Willd) and waterfern (Salvinia mimima Baker). Feeding also occurred on golden club (Orontium aquaticum L.) and one egg was laid on the terrestrial panda plant (Kalanchoe tomentosa Baker). Plants oviposited and fed upon were retested in choice tests. The weevils then fed and oviposited exclusively on waterlettuce. Various aspects of weevil biology, including larval feeding and mining, plant response to weevil attack, and adult behavior are discussed. Florida Agric. Expt. J. series No 8580.     

Arginine Silicate Inositol Complex Accelerates Cutaneous Wound Healing

The objective of this study was to assess the accumulation and depletion of cadmium in the blood, milk, hair, feces, and urine of Holstein cows during and after treatment. Three Holstein cows received daily oral cadmium administrations (as cadmium chloride) of 0.182 mg/kg body weight/day for 21 days followed by a 63-day withdrawal period. Blood, milk, hair, feces, and urine were collected during treatment and withdrawal periods. Cadmium concentrations were measured by inductively coupled plasma mass spectrometry (ICP-MS). Cadmium concentrations in blood (0.61–1.12 μg/L), milk (0.39–1.04 μg/L), and urine (0.41–2.05 μg/L) were low. Comparatively, cadmium concentrations in feces were higher, especially on treatment day 14 (20.11 mg/kg dry matter). Fecal cadmium concentrations decreased to baseline levels (0.12 mg/kg dry matter) on withdrawal day 21. Hair cadmium concentrations increased with treatment, reaching the highest levels on withdrawal day 7 (24.33 μg/kg). Most of the cadmium was excreted via the feces and very little was present in urine or milk. Cadmium residues were detected in blood and milk more than 63 days after cadmium withdrawal. Hair cadmium concentrations may reflect exposure to the metal.     

A microcosm investigation of fe (iron) removal using macrophytes of ramsar lake: A phytoremediation approach

The present study deals with the microcosm study of Fe (Iron) phytoremediation using Eichhornia crassipes, Lemna minor, Pistia stratiotes and Salvinia cucullata species collected from the Loktak Lake, a Ramsar Site which exists in north-eastern India (an Indo-Burma hotspot region). Efficiency of these four macrophytes was compared using different Fe concentrations of 1 mg L^?1, 3 mg L^?1 and 5 mg L^?1 for 4 days, 8 days and 12 days, respectively. E. crassipes was the most efficient macrophyte whereas L. minor was the least efficient. E. crassipes removed the highest percentage of Fe, i.e. 89% from 1 mg L^?1, 81.3% from 3 mg L^?1 and 73.2% from 5 mg L^?1 in 12-day experiment.     

The development of someLemnaceae under different nutrient conditions

Plants ofSpirodela polyrrhiza, Lemna gibba, L. minor andL. minuscula were grown experimentally in nutrient media under various nutrient conditions involving different concentrations and forms of nitrogen and different concentrations of phosphorus. The treatments affected the multiplication rate of the plants, their root length and formation of anthocyanin and of turions.     

DECREASE AND INCREASE PROFILE OF CU,CR AND PB DURING STABLE PHASE OF REMOVAL BY DUCKWEED (LEMNA MINOR L.)

The present work details the decrease-increase profiles of Cu, Cr, and Pb by the aquatic plant Lemna minor. A mixture of these metals were utilized at different concentrations. Removal profiles of each metal was determined with water samples taken every 24 h for a 144 h period after the 48 h mark and was examined with correlation analysis. Removal profiles of Cr and Pb by L. minor  from the mixture were observed to be highly similar with each other (r = 0.943). High proportion of Cr and Pb were removed compared to Cu and removal equations were defined with the aid of regression analysis.     

Differences specifiques entre les besoins quantitatifs en chlore deLemna minor,L. perpusilla etSpirodela polyrrhyza

Résumé Les symptômes de la carence en halogènes chezLemna minor, L. Perpusilla etSpirodella polyrrhyza sont très voisins.Les besoins en chlore des deux premières espèces sont particulièrement faibles. Exprimés en concentrations nécessaires pour atteindre 50 pour cent du maximum accessible de la récolte dans les conditions expérimentales décrites, ils sont respectivement de 7 et 3 µg de Cl^– par litre pourL. minor etL. perpusilla. La carence en halogènes est particulièrement difficile à obtenir chez ces deux espèces.Les besoins deSpirodela polyrrhyza dont la biologie et les conditions naturelles de vie sont très voisines de celles deL. minor sont beaucoup plus élevés, et exprimés de la même manière, égaux à 27 µg de Cl^– par litre. Cette espèce est, de ce fait, à recommander dans les recherches concernant les halogènes.

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Summary The symptoms of halogens deficiencies inLemna minor, L. perpusilla andSpirodela polyrrhyza are very similar.The chlorine requirements of the two first species are particularly small. Expressed in terms of concentrations giving 50 per cent of the available maximum crop, in the above mentioned experimental conditions, the data are 7 and 3 µg of Cl^– per liter forL. minor, andL. perpusilla respectively. The halogens deficiency is difficult to obtain particularly in those two species.The needs ofSpirodela polyrrhyza, the natural conditions of live and the biology of which are very similar to those ofL. minor, are much higher, and — expressed in the same way — amount to 27 µg of Cl^– per liter. This species s therefore to be recommended in work concerning halogens.

     

Effect of cations,including heavy metals,on cadmium uptake by Lemna polyrhiza L.

Cations, including calcium, magnesium, potassium, sodium, copper, iron, nickel and zinc, inhibited (up to 40%) extracellular binding and intracellular uptake of cadmium by Lemna polyrhiza in solution culture. Test plants showed a high capacity of extracellular cadmium binding which was competitively inhibited by copper, nickel and zinc; however, calcium, magnesium and potassium caused non-competitive inhibition. Iron and sodium increased K _m and decreased V _max, thereby causing mixed inhibition of extracellular binding. Intracellular cadmium uptake displayed Michaelis-Menten kinetics. It was competitively inhibited by calcium, magnesium, iron, nickel and zinc. Monovalent cations (sodium and potassium) caused non-competitive and copper caused mixed inhibition of intracellular cadmium uptake. Thus, high levels of cations and metals in the external environment should be expected to lower the cadmium accumulation efficiency of L. polyrhiza.     

Metabolic profiling, free-radical scavenging and tyrosinase inhibitory activities of Lemna minor whole plants cultivated in various concentrations of proline and sucrose

Metabolic profiling of Lemna minor whole plants cultivated in proline and sucrose at various concentrations was performed using gas chromatography-mass spectrometry coupled with multivariate statistical analysis. In total, 46 compounds including alkaloids, amino acids, fatty acids, organic acids, phenolics, phytosterols, purines, and sugars were assigned, and the relative levels of these metabolites were compared in the L. minor whole plant samples. Free-radical scavenging and tyrosinase inhibitory activities were also investigated in L. minor whole plants cultivated in proline and sucrose at various concentrations. The whole plants cultivated in 3% sucrose and 0.5 mM proline for 42 days exhibited the highest antioxidative and tyrosinase inhibitory activities, and biomass accumulation. Total phenolic content and cinnamic acid content were also highest under those conditions, which might have contributed to the free-radical scavenging and tyrosinase inhibitory activities. There were strong correlations between free-radical scavenging activity and total phenolic content, and between tyrosinase inhibition activity and cinnamic acid content in L. minor whole plants cultivated under various conditions.     

THE DISTRIBUTION AND TAXONOMIC SIGNIFICANCE OF LIGNIN IN THE LEMNACEAE

Lignification characteristics of 14 species of Lemnaceae were studied by the alkaline oxidation technique in an attempt to resolve conflicting reports of the presence of lignin and to provide chemotaxonomic data for supplementing previous systematic treatments. Four species of Spirodela, eight of Lemna, Wolffiella oblonga, and Wolffia microscopica were clonally subcultured, homogenized, exhaustively extracted and the insoluble residue oxidized in alkaline cupric hydroxide. Barley (Hordeum vulgare), Elodea densa and Spirogyra sp. were examined to validate the technique. The benzaldehydes were extracted, separated by thin-layer chromatography, and quantitated spectrophotometrically. Recovery of syringaldehyde, vanillin, and to a lesser extent p-hydroxybenzaldehyde, was accepted as evidence that these plants are lignified. The highest yields of syringaldehyde and vanillin were recovered from S. intermedia, the largest member of the Lemnaceae. Lesser amounts were obtained from S. polyrhiza and S. oligorhiza. Spirodela biperforata yielded no syringaldehyde which substantiates its distinctiveness from the morphologically similar S. polyrhiza. All Lemna species are nerved, yet vanillin (but not syringaldehyde) was recovered only from L. trinervis, L. perpusilla, L. minor, and L. minima. The species L. trisulca, L. gibba, L. obscura, and L. valdiviano yielded only p-hydroxybenzaldehyde. Thus the presence of nerves is not evidence for lignification within the genus Lemna, and the relationships suggested by their gross morphology are not supported by their lignin chemistry. Wolffiella is non-lignified by these criteria. Wolffia microscopica is the smallest flowernig plant and it has no nerves; vanillin was unexpectedly recovered and microscopic examination showed highly lignified anther walls.     

THE GROWTH OF DUCKWEEDS IN MINERAL NUTRIENT SOLUTIONS WITH AND WITHOUT ORGANIC EXTRACTS

1. Detmer''s solution and a modified Knop''s solution are unfavorable culture media for the growth of Spirodela polyrhiza. 2. When the modified Knop''s solution was diluted to 10 times its volume, Spirodela polyrhiza and Lemna valdiviana grew and reproduced for periods of 26 months and 21 months, respectively. 3. Growth in the dilute Knop''s solution, which alone can support the growth of Spirodela indefinitely, was considerably stimulated over a period of 23 days by adding to every liter the water-soluble material of 0.4 gm. autolyzed yeast, or the material of 2.5 gm. peat soluble in a 1 per cent solution of NaHCO₃. 4. The nature of the stimulus or of the protection afforded by the organic material is as yet unknown. 5. The necessity of organic accessory foods (auximones) in the nutrition of green plants cannot be accepted as an established fact.     

Bioremoval of Aqueous Lead Using Lemna Minor

The aquatic plant Lemna minor (duckweed) was examined for its ability to sorb soluble lead from water under laboratory conditions. The use of biomass as a sorption medium provides a simple alternative separation technology. Laboratory-scale (700-mL) batch reactors containing soil-based sediments were used to expose L. minor to concentrations of 0.0, 5.0, and 10.0 mg/L of lead for 7 d. Overall removal amounts of 95% were observed, with 85% removal occurring within the first day. A sorption process model was developed based on a mass balance and a power law rate of sorption equation.     

Evaluation of heat shock protein 70 as a biomarker of environmental stress in Fucus serratus and Lemna minor

Heat shock proteins (Hsps) are known to be induced in response to short-term stress. The present study aimed to evaluate the potential of Hsp70 as a biomarker of stress produced by increased temperature, osmotic pressure, and exposure to cadmium and sodium chloride in marine macroalgae and fresh water plant species. An indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) was developed with a working range of 0.025–10 μg?ml^?1 using a monoclonal antibody raised against purified Hsp70 of Phaseolus aureus (mung bean). Fucus serratus (toothed wrack), Chondrus crispus (Stackhouse or Carrageen moss), Ulva lactuca (sea lettuce) and Lemna minor (common duckweed) sample extracts were stressed for up to 24 h and then tested in the IC-ELISA. The presence of Hsp70 and cross-reactivity of the monoclonal antibody was confirmed by Western blot. The heat shock response was confirmed in each species using a 2-h 42°C treatment. Following heat shock, Hsp70 concentrations increased to a peak at 2 h (F. serratus) or 4 h (L. minor), after which concentrations decreased. Osmotic and cadmium stresses also resulted in elevated Hsp70 concentrations in samples of F. serratus and L. minor when compared with unstressed controls. In both, osmotic and metal stress, the production of Hsp70 increased to a maximum and subsequently decreased as the stressor levels increased. Results suggest that Hsp70 IC-ELISA could potentially be applied to the detection of stress in these aquatic species, although it would probably be most effective when used in conjunction with other measurements to provide a stressor-specific biomarker profile or fingerprint.