Enhancing phytoremediative ability of Pisum sativum by EDTA application

The aim of our research was to demonstrate how the presence of EDTA affects resistance of pea plants to Pb and Pb-EDTA presence, and to show the effectivity of lead ions accumulation and translocation. It was determined that EDTA not only increased the amount of Pb taken up by plants but also Pb ion transport through the xylem and metal translocation from roots to stems and leaves. It can be seen in the presented research results that addition of the chelator with Pb limited metal phytotoxicity. We also demonstrated a significant effect of EDTA not only on Pb accumulation and metal transport to the aboveground parts but also on the profile and amount of thiol compounds: glutathione (GSH), homoglutathione (hGSH) or phytochelatins (PCs), synthesized by the plants. We observed a significant effect of the synthetic chelator on increasing the level of Pb accumulation in roots of plants treated with Pb including EDTA (0.5 and 1 mM). Pisum sativum plants treated only with 1 mM Pb(NO3)2 accumulated over 50 mg Pb x g(-1) dry wt during 4 days of cultivation. Whereas in roots of pea plants exposed to Pb+0.5 mM EDTA 35% more Pb was observed. When 1 mM EDTA was applied roots of pea accumulated over 67% more metal. The presence of EDTA also increased metal uptake and transport to the aboveground parts. In pea plants treated only with 1 mM lead nitrate less than 3 mg Pb x g(-1) dry wt was transported, whereas in P. sativum treated with Pb-EDTA doubled amount of Pb was observed in stems and leaves.     

EFFECT OF INDOLE-3-ACETIC ACID,KINETIN, AND ETHYLENEDIAMINETETRAACETIC ACID ON PLANT GROWTH AND UPTAKE AND TRANSLOCATION OF LEAD,MICRONUTRIENTS, AND MACRONUTRIENTS IN ALFALFA PLANTS

Alfalfa plants germinated and grown for 15 d in soil containing 80 mg Pb kg^?1 were treated with ethylenediaminetetraacetic acid (EDTA) at 0.8 mM and indole-3-acetic acid-kinetin (IAA-KN) at 100 μM. Fifteen days after the treatment application, the concentration of lead (Pb), macronutrients, and micronutrients was determined using inductively coupled plasma/optical emission spectroscopy. The chlorophyll content and plant growth were also measured. Roots of plants exposed to Pb alone, Pb–EDTA, and Pb–EDTA-IAA-KN had 160, 140, and 150 mg Pb kg^?1 DW, respectively. Pb was not detected in the stems of plants exposed to Pb alone; however, stems of plants treated with EDTA and EDTA–IAA-KN had 78 and 142 mg Pb kg^?1 DW, respectively. While the Pb concentration in leaves of plants treated with EDTA and EDTA–IAA-KN was 92 and 127 mg kg^?1 DW, respectively. In addition, EDTA and EDTA–IAA-KN significantly increased the translocation of zinc and manganese to leaves. The x-ray absorption spectroscopic studies demonstrated that Pb(II) was transported from roots to leaves without a change in the oxidation state.     

Accumulation of lead in root cells of Pisum sativum

The ever-increasing environmental pollution necessitates organisms to develop specific defense systems in order to survive and function effectively. Lead is taken up by plants mainly through roots and over 96% are accumulated there.Pea plants were cultivated hydroponically for 4 days with 0.1, 0.5 and 1 mM Pb(NO₃)₂. Uptake of lead ions from nutrient solution and accumulation in root stems and leaves during 96-h cultivation was estimated. The root tip cells were observed with transmission electron microscope to analyse their ultrastructure and lead localization. Pb was accumulated in the cell wall, cell membrane, vacuoles, mitochondria and peroxisomes. The fractions of mitochondria and peroxisomes were isolated from pea roots purified by means Percoll gradient, and were observed by means of electron microscope with the attachment for X-ray microanalysis. Visible deposits containing Pb were observed in both cell organelles.     

Physiological and ultrastructural effects of lead on tobacco

The effects of lead toxicity on leaf gas exchange, chlorophyll content, chlorophyll fluorescence, chloroplast ultrastructure, and opening of stomata were examined in tobacco (Nicotiana tabacum L.) plants. Plants were grown in a growth chamber for 7 d in Hoagland nutrient solution supplemented with 0.0 (control), 5, 10, 25, 50, 100, 300 and 500 μM Pb(NO₃)₂. Plants treated with 5, 10, and 25 μM Pb(NO₃)₂ exhibited no abnormalities. Root and shoot growth, net photosynthetic rate and stomatal conductance were significantly reduced in plants treated with 100, 300 and 500 μM Pb(NO₃)₂. In plants treated with 500 μM Pb(NO₃)₂, the majority of stomata were closed. The effect of Pb(NO₃)₂ on chlorophyll content and chlorophyll fluorescence parameters was negligible. However, in plants exposed to 100, 300, and 500 μM Pb(NO₃)₂, the mesophyll cells showed altered chloroplasts with disrupted thylakoid membranes.     

Effect of Pb ions on superoxide dismutase and catalase activities in leaves of pea plants grown in high and low irradiance

The role of irradiance on the activity of antioxidant enzymes: superoxide dismutase (SOD) and catalase (CAT) was examined in the leaves of Pisum sativum L. plants grown under low (LL) or high (HL) irradiance (PPFD 50 or 600 μmol m⁻² s⁻¹) and exposed after detachment to 5 mM Pb (NO₃)₂ for 24 h. The activities of both enzymes increased in response to LL compared with HL and no effect of Pb ions was observed. Photosystem (PS) 1 and PS 2 activities were also investigated in chloroplasts isolated from these leaves. LL lowered PS 1 electron transport rate and changes in photochemical activity of PS 1 induced by Pb²⁺ were visible only in the chloroplasts isolated from leaves of LL grown plants. PS 2 activity was influenced similarly by Pb ions at both PPFD. This study demonstrates that leaves of HL grown plants were less sensitive to lead toxicity than those from LL grown plants. Changes in electron transport rates were the main factors responsible for the generation of reactive oxygen species in the chloroplasts and as a consequence, in induction of antioxidant enzymes.     

The effect of EDTA and EDDS on lead uptake and localization in hydroponically grown Pisum sativum L.

Pisum sativum plants were treated for 3 days with an aqueous solution of 100 μM Pb(NO₃)₂ or with a mixture of lead nitrate and ethylenediaminetetraacetic acid (EDTA) or [S,S]-ethylenediaminedisuccinic acid (EDDS) at equimolar concentrations. Lead decline from the incubation media and its accumulation and localization at the morphological and ultrastructural levels as well as plant growth parameters (root growth, root and shoot dry weight) were estimated after 1 and 3 days of treatment. The tested chelators, especially EDTA, significantly diminished Pb uptake by plants as compared to the lead nitrate-treated material. Simultaneously, EDTA significantly enhanced Pb translocation from roots to shoots. In the presence of both chelates, plant growth parameters remained considerably higher than in the case of uncomplexed Pb. Considerable differences between the tested chelators were visible in Pb localization both at the morphological and ultrastructural level. In Pb+EDTA-treated roots, lead was mainly located in the apical parts, while in Pb+EDDS-exposed material Pb was evenly distributed along the whole root length. Transmission electron microscopy and EDS analysis revealed that in meristematic cells of the roots incubated in Pb+EDTA, large electron-dense lead deposits were located in vacuoles and small granules were rarely noticed in cell walls or cytoplasm, while after Pb+EDDS treatment metal deposits were restricted to the border between plasmalemma and cell wall. Such results imply different ways of transport of those complexed Pb forms.     

Uptake and accumulation of lead by roots,hypocotyls and shoots of Indian mustard [Brassica juncea (L.)]

The effects of different concentrations of lead nitrate on root, hypocotyl and shoot growth of Indian mustard (Brassica juncea var. Megarrhiza), and the uptake and accumulation of Pb²⁺ by its roots, hypocotyls and shoots were investigated in the present study. The concentrations of lead nitrate (Pb(NO₃)₂) used were in the range of 10⁻⁵–10⁻³ M. Root growth decreased progressively with increasing concentration of Pb²⁺ in solutions. The seedlings exposed to 10⁻³ M Pb exhibited substantial growth reduction and produced chlorosis. Brassica juncea has considerable ability to remove Pb from solutions and accumulate it. The Pb content in roots of B. juncea increased with increasing solution concentration of Pb²⁺. The amount of Pb in roots of plants treated with 10⁻⁴, 10⁻³ and 10⁻⁵ M Pb²⁺ were 184-, 37- and 6-fold, respectively, greater than that of roots of the control plant. However, the plants transported and concentrated only a small amount of Pb in their hypocotyls and shoots, except for the group treated with 10⁻³ M Pb²⁺.     

Induced Phytoextraction of Lead Through Chemical Manipulation of Switchgrass and Corn; Role of Iron Supplement

The effects of combined chemical application of benomyl, ethylenedianinetetraacetate (EDTA), and iron (Fe) (foliar and root) on lead (Pb) phytoextraction by switchgrass (Panicum virgatum) and corn (Zea mays) was examined. Switchgrass was grown in Pb-contaminated urban topsoil with the following treatments: (C) Control, (B) benomyl, (E) EDTA, (F) foliar-Fe, (BE) benomyl + EDTA, (BF) benomyl + foliar-Fe, (FE) foliar-Fe + EDTA, (BFE) benomyl + foliar-Fe + EDTA. Corn was grown in sand-culture supplemented with Pb (500 mg kg^?1) with the following treatments: (C) control, (B) benomyl, (E) EDTA, (F) root-Fe, (BE) benomyl + EDTA, (BF) benomyl + root-Fe, (FE) root-iron + EDTA, and, (BFE) benomyl + root-Fe + EDTA. All treatments were replicated three times and pots were arranged in a completely randomized design. Plants were analyzed for element concentration (Fe, Zn, P, and Pb) using either inductively coupled plasma (argon) atomic emission spectroscopy (ICP-AES) or graphite furnace atomic absorption spectrometer. Iron supplementation (foliar and root) affected Pb-translocation in plants. Foliar-Fe treatment increased translocation ratio of Pb (TF-Pb) significantly compared to other treatments with the exception of plants treated with benomyl and BF. Root-Fe treatment in combination with EDTA (FE) increased TF-Pb significantly compared to other treatments. Phytoextraction was improved by the combined chemical application; plants treated with BFE treatment increased Pb-total-phytoextraction by 424% compared to Control plants.     

Biosorption and bioaccumulation of lead by Penicillium sp. Psf-2 isolated from the deep sea sediment of the Pacific Ocean

A lead resistant fungus was isolated from the Pacific sediment. It was associated with Penicillium according to its partial sequences of 18S and ITS. The fungus could grow in the presence of 24 mM Pb(NO₃)₂ in a liquid medium, and no growth inhibition was observed at 4 mM and below. When growing in the presence of 4 mM Pb(NO₃)₂, the fungus accumulated a large amount of lead granules in the cell, as well as adsorbed on the outer layer of cell wall, as observed under a transmission electron microscope. The intracellular lead deposited either in the vicinity of the cytoplasm membrane or in the vacuoles, and also could aggregate into large particles in the cytoplasm. However, lead was not adsorbed on the thick inner wall of the fungus. Energy dispersive X-ray spectroscopy analysis showed that these granules or particles mainly consisted of lead, and other elements could hardly be detected. Selected area electron diffraction analysis showed that there were regular crystalline lattices in the lead precipitates, indicating that they were actually in the form of crystals to some extent. Therefore, both intracellular bioaccumulation and extracellular biosorption had contributed to the high resistance of this fungus to lead. These results suggest that this fungus can be used in biotreatment as a lead trapper.     

Effect of lead stress on mineral content and growth of wheat (Triticum aestivum) and spinach (Spinacia oleracea) seedlings

Lead (Pb) is the most common heavy metal contaminant in the environment. Pb is not an essential element for plants, but they absorb it when it is present in their environment, especially in rural areas when the soil is polluted by automotive exhaust and in fields contaminated with fertilizers containing heavy metal impurities. To investigate lead effects on nutrient uptake and metabolism, two plant species, spinach (Spinacia oleracea) and wheat (Triticum aestivum), were grown under hydroponic conditions and stressed with lead nitrate, Pb(NO₃)₂, at three concentrations (1.5, 3, and 15 mM).Lead is accumulated in a dose-dependent manner in both plant species, which results in reduced growth and lower uptake of all mineral ions tested. Total amounts and concentrations of most mineral ions (Na, K, Ca, P, Mg, Fe, Cu and Zn) are reduced, although Mn concentrations are increased, as its uptake is reduced less relative to the whole plant’s growth. The deficiency of mineral nutrients correlates in a strong decrease in the contents of chlorophylls a and b and proline in both species, but these effects are less pronounced in spinach than in wheat. By contrast, the effects of lead on soluble proteins differ between species; they are reduced in wheat at all lead concentrations, whereas they are increased in spinach, where their value peaks at 3 mM Pb.The relative lead uptake by spinach and wheat, and the different susceptibility of these two species to lead treatment are discussed.     

Effects of Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> stress on oxidative damage,antioxidant enzymes activities and polyamine contents in roots of grafted and non-grafted tomato plants

The effects of Ca(NO₃)₂ stress on biomass production, oxidative damage, antioxidant enzymes activities and polyamine contents in roots of grafted and non-grafted tomato plants were investigated. Results showed that when exposed to 80 mM Ca(NO₃)₂ stress, the biomass production reduction in non-grafted plants was more significant than that of grafted plants. Under Ca(NO₃)₂ stress, superoxide anion radical (O₂•⁻) producing rate, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents of non-grafted plants roots were significantly higher than those of grafted plants, however, nitrate (NO₃ ⁻), ammonium (NH₄ ⁺) and proline contents, superoxide dismutase (SOD, EC1.15.1.1), peroxidase (POD, EC1.11.1.7), catalase (CAT, EC1.11.1.6) and arginine decarboxylase (ADC, EC 4.1.1.19) activities of grafted plants roots were significantly higher than those of non-grafted plants. Regardless of stress, free, conjugated and bound polyamine contents in roots of grafted plants were significantly higher than those of non-grafted plants. The possible roles of antioxidant enzymes, prolines and polyamines in adaptive mechanism of tomato roots to Ca(NO₃)₂ stress were discussed. Gu-Wen Zhang and Zheng-Lu Liu contributed equally to this work.     

EDTA-Facilitated Phytoremediation of Soil with Heavy Metals from Sewage Sludge

The objective of this research was to determine the effect of the chelate EDTA (ethylenediaminetetraacetic acid), which is used in phytoremediation, on plant availability of heavy metals in liquid sewage sludge applied to soil. Sunflower (Helianthus annuus L.) was grown under greenhouse conditions in a commercial potting soil; the tetrasodium salt of EDTA (EDTA Na₄) was added at a rate of 1 g kg^-1 to half the pots. Immediately after seeds were planted, half of the pots with each soil (with or without EDTA) were irrigated with 60 ml sludge, and half were irrigated with 60 ml tap water. For the subsequent five irrigations, plants in soil with EDTA received either sludge or tap water containing 0.5 g EDTA Na₄ per 1000 ml, and plants in soil without EDTA received sludge or tap water without EDTA. Of the four heavy metals whose extractable concentrations in the soil were measured (Cu, Fe, Mn, and Zn), only Zn had a higher concentration in sludge-treated soil with EDTA compared to sludge-treated soil without EDTA. The concentrations of Fe, Cu, and Mn were similar in sludge-treated soil with and without EDTA. Of the three heavy metals whose total concentrations in the soil were measured (Cd, Pb, Cr), Pb (<10 mg kg^-1) and Cd (< 1 mg kg^-1) were below detection limits, and Cr was unaffected by treatment. The concentration of all measured elements in plants (Cd, Cu, Fe, Zn, Pb) was higher than the concentrations measured in the soil. With no EDTA, sludge-treated plants had a higher concentration of the five heavy elements than plants grown without sludge. Cadmium was lower in sludge-treated plants with EDTA than plants with EDTA and no sludge. After treatment with EDTA, the concentrations of Cu, Fe, and Zn were similar in plants with and without sludge. Lead was higher in plants with EDTA than plants without EDTA, showing that EDTA can facilitate phytoremediation of soil with Pb from sewage sludge.     

Effect of lead on the physiological,biochemical and ultrastructural properties of Leucaena leucocephala

• Heavy metals are characterised by a relatively high density and cause genotoxic, cytotoxic and mutagenic effects on plants, animals and humans. Lead (Pb) is one of the heavy metals that causes toxicity to plants and animals.
• This experiment was conducted using a hydroponic technique to study the effects of Pb(NO₃)₂ on physiological, biochemical and ultrastructural characteristics in Leucaena leucocephala seedlings. Plants were grown in a growth chamber for 21 days in Hoagland’s solution supplemented with 0 (control), 25, 50, 100, 300, 500 and 700 µm Pb(NO₃)₂.
• Shoot heights as well as root lengths decreased significantly in Pb‐treated plants with 300, 500 and 700 µm . In Pb‐treated plants with high Pb concentrations, photosynthesis rate (P_N), stomatal conductance (g_s) and transpiration rate (E) decreased. Total protein and carbohydrate content in Pb‐treated plants with 300, 500 and 700 µm increased significantly in leaves. Moreover, in Pb‐treated plants with 300, 500 and 700 µm Pb(NO₃)₂, mesophyll cells had enlarged chloroplasts with disrupted thylakoid membranes associated with large starch grains. In contrast, Pb treatments with 25, 50 µm and 100 µm were not toxic to the plants. Thick sections of roots of Pb‐treated plants with 300, 500 and 700 µm Pb showed distinct changes in structure of epidermal and cortical cells. Moreover, thin sections of roots of Pb‐treated plants with 300, 500 and 700 µm Pb had thickened walls of xylem cells.
• These results will shed more light in understanding the effects of heavy metal stress on plants.

     

Insights into the growth response and nitrogen accumulation and use efficiency of the Poaceae grass <Emphasis Type="Italic">Brachypodium distachyon</Emphasis> to high nitrogen availability

Optimization of nitrogen (N) use by grasses is a central issue of the current work. The effects of different N concentrations (0, 0.25, 0.5, 1.0, 2.5, and 5.0 mM NH₄NO₃) on growth of Brachypodium distachyon were assessed on controlled hydroponic culture. Maximal growth (132% of control) was obtained at 0.5 mM NH₄NO₃, critical N level, and was maintained at higher N concentrations. The highest N level (5.0 mM) has a similar effect on growth as 0.5 mM NH₄NO₃. It has no significant effects on water status, and total and reduced N contents in shoots while, increased those in roots, compared to plants receiving 0.5 mM NH₄NO₃. The high N availability, however, increased nitrate contents in shoots and roots by 3- and 20-folds, respectively, compared to those of plant receiving 0.5 mM NH₄NO₃. In addition, high N availability reduced the nitrogen use efficiency (NUE) by 18% compared to that of plant receiving only 0.5 NH₄NO₃. In view of B. distachyon productivity and environmental concerns, it is concluded that the critical level of N application should be 0.5 mM NH₄NO₃ and the excess fertilization led to a high nitrate accumulation.     

Comparison of antioxidant responses to cadmium and lead in Bruguiera gymnorrhiza seedlings

Seedlings of mangrove plant Bruguiera gymnorrhiza cultured in sand with Hoagland’s nutrient solution were treated with 1 to 30 mM Cd(NO₃)₂ or Pb(NO₃)₂ for 2 months. In all Cd/Pb treatments, the malondialdehyde content increased while the chlorophyll content declined. Peroxidase (POD) and superoxide dismutase (SOD) activities in roots increased at moderate Cd/Pb concentrations (1–10 mM), whereas decreased at higher concentrations (20–30 mM). Catalase (CAT) activity in roots was inhibited by 1–10 mM Cd but enhanced by 1–10 mM Pb. The activities of POD, SOD and CAT in leaves were less affected by Cd and Pb than in roots. A new SOD and three CAT isoenzymes were induced by Pb. In contrast, no additional SOD and CAT isoenzymes were induced by Cd.     

EDTA-assisted heavy-metal uptake by poplar and sunflower grown at a long-term sewage-sludge farm

Little information is available concerning the efficacy of chelates applied to biosolids (sewage-sludge)-treated soil for heavy-metal removal. The purpose of the experiment was to determine the availability to sunflower (Helianthus annuus L.) and hybrid poplar (Populus deltoides Marsh. × P. nigra L.) seedlings, of non-essential (Cd, Ni, Pb) and essential heavy metals (Cu, Fe, Mn, Zn) in field soil injected with biosolids since 1976 and treated with ethylenediamine-tetraacetic acid (EDTA) in 2001. Sunflower was grown at two densities, 20000 and 60000 plants/ha, and poplar at 10000 plants/ha. The tetrasodium salt of EDTA was applied at rates of 0, 0.5, 1, and 2 g EDTA salt per kg surface (25-cm depth) soil. The EDTA did not affect uptake by poplar of the three non-essential (Cd, Ni, Pb) and four essential (Cu, Fe, Mn, Zn) heavy metals. For sunflower, the 1.0 g/kg rate of chelate addition resulted in maximal removal of the three non-essential heavy metals (Cd, Ni, Pb). Uptake of the essential heavy metals by sunflower was little affected by the EDTA. At the 20000 plants/ha density, leaves of sunflower grown with 1.0 g EDTA Na₄2H₂O per kg soil accumulated more Cd, Ni, and Pb than leaves of sunflower grown without the EDTA salt. At this density, concentrations of Cd in leaves of sunflower without EDTA and with 1.0 g/kg EDTA salt were 2.2 and 6.5 g/g, respectively; for Ni, they were 6.7 and 19.2 g/g, respectively; and for Pb, they were 15.6 and 46.9 g/g, respectively. At the 60000 plants/ha density, stems of sunflower grown with 1.0 g EDTA Na₄2H₂O per kg soil accumulated more Cd, Ni, and Pb than stems of sunflower grown without the EDTA salt. At this density, concentrations of Cd in stems of sunflower without EDTA and with 1.0 g/kg EDTA salt were 0.6 and 4.6 g/g, respectively; for Ni, they were 1.7 and 17.6 g/g, respectively; and for Pb, they were 5.2 and 42.8 g/g, respectively. Removal of the non-essential heavy metals by sunflower was greater at the higher plant density (60000 plants/ha) compared to the lower one (20000 plants/ha).     

Transgenic rice with low sucrose-phosphate synthase activities retain more soluble protein and chlorophyll during flag leaf senescence

We investigated whether changes in sucrose-phosphate synthase (EC 2.4.1.14, SPS) activity could alter N remobilization during leaf senescence. Transgenic rice (Oryza sativa L. cv. Nipponbare) with low SPS activities and wild-type rice plants were grown with basal N (1.0 mM NH₄NO₃) until the late vegetative stage. Subsequently, half of the plants were transferred to a low N (0.1 mM NH₄NO₃) condition to accelerate leaf senescence, and the others were continuously grown with basal N. With low N supply, the amounts of chlorophyll and soluble protein in flag leaf blades decreased after anthesis in both the low SPS plants and wild-type plants, although the decrease was less in the low SPS plants. Panicle weights were significantly lower in the low SPS plant than in the wild-type plant. These results suggest that the remobilization of N from flag leaves was diminished by suppressing the development of reproductive sinks in the low SPS plant.     

Increased cucumber salt tolerance by grafting on pumpkin rootstock and after application of calcium

Self-grafted and pumpkin rootstock-grafted cucumber plants were subjected to the following four treatments: 1) aerated nutrient solution alone (control), 2) nutrient solution with 10 mM Ca(NO₃)₂ (Ca), 3) nutrient solution with 90 mM NaCl (NaCl), and 4) nutrient solution with 90 mM NaCl + 10 mM Ca(NO₃)₂ (NaCl+Ca). The NaCl treatment decreased the plant dry mass and content of Ca²⁺ and K⁺ but increased the Na⁺ content in roots and shoots. Smaller changes were observed in pumpkin rootstock-grafted plants. Supplementary Ca(NO₃)₂ ameliorated the negative effects of NaCl on plant dry mass, relative growth rate (RGR), as well as Ca²⁺, K⁺, and Na⁺ content especially for pumpkin rootstock-grafted plants. Supplementary Ca(NO₃)₂ distinctly stimulated the plasma membrane (PM) H⁺-ATPase activity which supplies the energy to remove excess Na⁺ from the cells. The expressions of gene encoding PM H⁺-ATPases (PMA) and gene encoding a PM Na⁺/H⁺ antiporter (SOS1) were up-regulated when Ca(NO₃)₂ was applied. The pumpkin rootstock-grafted plants had higher PM H⁺-ATPase activity as well as higher PMA and SOS1 expressions than the self-grafted plants under NaCl + Ca treatment. Therefore, the addition of Ca²⁺ in combination with pumpkin rootstock grafting is a powerful way to increase cucumber salt tolerance.     

A strategy of Ca2+ alleviating Na+ toxicity in salt-treated Cyclocarya paliurus seedlings: photosynthetic and nutritional responses

Cyclocarya paliurus seedlings were subjected to 85?mM NaCl and 0, 6, 12 or 18?mM Ca(NO₃)₂ treatments to study changes in plant growth, photosynthetic parameters and distribution and/or accumulation of organic and inorganic solutes. Na⁺ toxicity symptoms were observed in plants non-treated with Ca(NO₃)₂, while 12?mM Ca(NO₃)₂ supplementation produced a significant promotion of shoot growth; meanwhile chlorophyll content, photosynthetic rate and optimum quantum yield of photosystem II (PSII), represented by the F_v/F_m ratio and pigments content as well as proline and soluble sugars, significantly increased. Ca(NO₃)₂ supply increased K⁺ and Ca²⁺ concentration, whereas the Na⁺ transport to the shoot was inhibited. There was a strong increase in the K⁺/Na⁺ ratio in shoot of Ca(NO₃)₂-treated plants. X-Ray microanalysis of roots showed that K⁺, Ca²⁺ and Na⁺ accumulated mainly in the epidermal cells and cortical cells of roots with 12?mM Ca(NO₃)₂ supply, and low accumulation was observed in stelar parenchyma, indicating exogenous Ca²⁺ possibly induced or strengthened effects of Casparian bands on ion transport. These results suggest that Ca(NO₃)₂ supplement increased inorganic and organic solutes accumulation in shoot and leaf, and restricted Na⁺ transport to the shoot by reinforcing barrier effects for attenuating salt injuries in plants, which could be a strategy of Ca²⁺ alleviating Na⁺ toxicity in C. paliurus seedlings subjected to salt stress.