Analysis of intercellular cadmium forms in roots and leaves of bush bean

Abstract

We characterized and quantified the chemical form of cadmium (Cd) in intercellular solutions of the apparent free space (AFS) of roots and leaves of bush bean plants. Plants were grown in sand and treated daily for five days with Hoagland nutrient solution containing, respectively, 0.5 and 1 mM Cd(NO₃)2. The intercellular solution was collected by infiltration‐extraction procedure using successively distilled water, 5 mM CaCl₂, and 5 mM EDTA in order to collect separately the water soluble, exchangeable, and complexed Cd. The ability of extradant solutions to remove Cd from the AFS of roots and leaves was: H2O < CaCl₂ ? EDTA, confirming that most of Cd was bound at the cell wall. Voltarimetric technique showed that water‐soluble Cd in intercellular solutions of the root and leaf tissues was as the Cd²⁺ ion, suggesting that Cd might be taken up by the roots and transported to leaves as the free ion.     

Einfluß von Ca2+ und pH auf das Fettsäuremuster von Phospholipiden der Rapswurzel (Brassica napus L.)

Effect of Ca²⁺ and pH upon the fatty acid composition of phospholipids from roots of rape plants (Brassica napus L.) The influence of Ca²⁺ and pH upon the dry matter of the shoot and the root of rape plants (Brassica napus L.) as well as upon the accumulation of nutrients in the shoot and the fatty acid composition of phosphatidyl ethanolamine (PÄ) and phosphatidyl choline (PC) from rape plant roots was tested by means of a water culture experiment. The experiment was designed with two concentrations of Ca-nutrition (3 mM and 0,03 mM CaCl₂ · 6 H₂O) and with three levels of pH (3,5; 5; 8) on the basis of four replications. The amounts and percentages of macro nutrients in the shoot indicated a specific effect on ion uptake by the treatments. K and Mg absorbed as cations were accumulated most intensively in the shoot at pH 5 whereas P absorbed as an anion was accumulated independent of pH at the same Ca-concentration. The fatty acid composition of PÄ and PC was distinctly dependent on the treatments. With regard to linolenic acid it appeared that Ca-nutrition may soften the harmful effect of a high H⁺-concentration. The results were discussed in relation to membrane functions.     

Ionic interactions and salinity affect monoterpene and phenolic diterpene composition in rosemary (Rosmarinus officinalis)

In this study, we evaluated how increased cation supply can alleviate the toxic effects of NaCl on plants and how it affects essential oils (EOs) and phenolic diterpene composition in leaves of rosemary (Rosmarinus officinalis L.) plants grown in pots. Two concentrations of the chloride salts KCl, CaCl₂, MgCl₂, and FeCl₃ were used together with 100 mM NaCl to study the effects of these nutrients on plant mineral nutrition and leaf monoterpene, phenolic diterpene, and EO composition. The addition of 100 mM NaCl, which decreased K⁺, Ca²⁺, and Mg²⁺ concentrations with increasing Na⁺ in leaves, significantly altered secondary metabolite accumulation. Addition of MgCl₂ and FeCl₃ altered leaf EO composition in 100 mM NaCl–treated rosemary plants while KCl and CaCl₂ did not. Furthermore, addition of CaCl₂ promoted the accumulation of the major phenolic diterpene, carnosic acid, in the leaves. The carnosol concentration was reduced by the addition of KCl to salt‐stressed plants. It is concluded that different salt applications in combination with NaCl treatment may have a pronounced effect on phenolic diterpene and EO composition in rosemary leaves thus indicating that ionic interactions may be carefully considered in the cultivation of these species to achieve the desired concentrations of these secondary metabolites.     

盐胁迫下外源钙对高羊茅种子萌发和幼苗离子分布的影响

该文模拟了上海市临港新成陆地盐渍化土壤的盐分特点,并在100 mmol/L NaCl盐胁迫下,以常见牧草和草坪草高羊茅（Festucaarundinacea）为材料,在人工气候室可控制条件下,进行了盐胁迫下种子萌发和幼苗盆栽试验,用不同浓度的CaCl2（5、10、20、40、80 mmol/L）处理,研究高羊茅种子萌发和幼苗生长状况,重点研究了矿质元素Na^＋、K^＋、Ca^2＋和Mg^2＋在植株地上部分和地下部分的分布。研究表明：适当浓度的外源CaCl2浸种处理能缓解高羊茅种子受到的盐胁迫伤害,促使种子提前萌发,20 mmol/L CaCl2浸种处理能显著提高种子萌发率,但高浓度（80 mmol/L）的外源钙处理对高羊茅种子萌发不利;适当浓度的CaCl2处理能促进幼苗地上部分生长,降低高羊茅根冠比、稳定植物细胞膜、维持离子平衡、提高植物耐盐性,但是高浓度（80 mmol/L）CaCl2处理会对植物幼苗生长造成伤害。     

Ecological Risk Assessment of Alfalfa Medicago Varia L.) Genetically Engineered to Express a Human Metallothionein (hMT) Gene

The objectives of these studies were two-fold: (1) to determine efficacy of low and high expression hMT gene constructs by assessing accumulation of Cu in shoots of parental and transgenic plants of alfalfa (Medicago varia L.) exposed to different concentrations of CuSO₄ by addition of CuSO₄ solutions to soil and (2) to identify potential unintended effects of the genetic engineering on root and shoot biomass, shoot nutrient content, arbuscular mycorrhizal infection and on the metabolic functions of microbial communities in the rhizosphere. In the absence of exogenous CuSO₄ additions to soil shoot biomass and the macronutrient (C, P, K, Ca, Mg and N) content of plants expressing hMT were not significantly different from the parental control. In the 0.5 mM and 1.0 mM CuSO₄ treatments transgenic plants expressing the commonly used transgenic β-glucuronidase (GUS) marker had significantly higher Fe content than the parental genotype. Significant differences were observed in the carbon substrate utilization patterns of rhizosphere microbial communities among the transgenic plants; no significant differences were observed in the percent mycorrhizal infection of parental and transgenic plants. Shoot biomass increased significantly in all genotypes treated with 0.5 mM CuSO₄ and decreased in all genotypes at CuSO₄ concentrations of 1.5 mM and 2.0 mM. Root dry weights decreased significantly in all genotypes at concentrations of 1.0 mM, 1.5 mM and 2.0 mM CuSO₄. The largest decreases in root dry weight were observed in hMT genotypes grown in soil treated with 1.5 and 2.0 mM CuSO₄. In plants treated with 1.5 mM CuSO₄, shoots of transgenic plants expressing the hMT gene accumulated nominally, but not statistically significantly higher levels of Cu in shoot tissue. Our results were surprising with regard to lack of sufficient efficacy of the current hMT constructs for significant accumulation of Cu from soil treated with CuSO₄. However, our results suggest the utility of applying adverse levels of CuSO₄ or other environmental stressors to identify potential unintended effects of genetic engineering that may not be apparent under typically more optimal plant growth test conditions.     

Responses of Batis maritima plants challenged with up to two‐fold seawater NaCl salinity

Batis maritima is a promising halophyte for sand‐dune stabilization and saline‐soil reclamation. This species has also applications in herbal medicine and as an oilseed crop. Here, we address the plant response to salinity reaching up to two‐fold seawater concentration (0–1000 mM NaCl), with a particular emphasis on growth, water status, mineral nutrition, proline content, and photosystem II integrity. Plant biomass production was maximal at 200 mM NaCl, and the plants survived even when challenged with 1000 mM NaCl. Plant water status was not impaired by the high accumulation of sodium in shoots, suggesting that Na⁺ compartmentalization efficiently took place in vacuoles. Concentrations of Mg²⁺ and K⁺ in shoots were markedly lower in salt‐treated plants, while that of Ca²⁺ was less affected. Soluble‐sugar and chlorophyll concentrations were hardly affected by salinity, whereas proline concentration increased significantly in shoots of salt‐treated plants. Maximum quantum efficiency (F_v/F_m), quantum yield of PSII (Φ_PSII), and electron‐transport rate (ETR) were maximal at 200–300 mM NaCl. Both nonphotochemical quenching (NPQ) and photochemical quenching (qP) were salt‐independent. Interestingly, transferring the plants previously challenged with supraoptimal salinities (400–1000 mM NaCl) to the optimal salinity (200 mM NaCl) substantially restored their growth activity. Altogether, our results indicate that B. maritima is an obligate halophyte, requiring high salt concentrations for optimal growth, and surviving long‐term extreme salinity. Such a performance could be ascribed to the plant capability to use sodium for osmotic adjustment, selective absorption of K⁺ over Na⁺ in concomitance with the stability of PSII functioning, and the absence of photosynthetic pigment degradation.     

Einfluß von Makrobicyclus „Kryptofix 222”︁ auf die Calcium- und Strontium-Aufnahme von Buschbohnen-Keimpflanzen

Influence of macrobicycle ?Kryptofix 222”? on calcium- and strontium-uptake of bush bean seedlings Macrobicycle ?Kryptofix 222”? (4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo-8,8,8-hexacosane) is the only known organic compound which chelates Sr (pK = 8.0) stronger than Ca (pK = 4.4). Therefore it was proved in experiments with 10 days old seedlings of bush beans, whether Kryptofix enables plants to discriminate between the physiological important Ca and the undesired Sr in favour of Ca. The following results were obtained: 1. At a constant (equimolar) supply of CaCl2 + SrCl₂ (50 μM/l each) increasing levels of Kryptofix raised the Ca/Sr-ratio of the seedlings from 0.8 (without Kryptofix) to 2.7 (with 150 μM Kryptofix/l) by reducing their Sr-content and increasing their Ca-content correspondingly. 2. Despite of reduced Sr-uptake the translocation of Sr to the primary leaves was promoted by Kryptofix (presumably via preventation of Sr fixation by the xylem vessels and in the surrounding tissue), whereas no influence exists on the movement of Ca. 3. At low CaCl₂ + SrCl₂ supply (5 μM/l each) the bean seedlings showed similar Ca and Sr-contents (Ca/Sr-ratio about 1.07), both in the presence or absence of equimolar Kryptofix concentrations. 4. With increasing CaCl₂ + SrCl₂ supplies (25–125 μM/l each), bean seedlings without Kryptofix increasingly favours Sr- against Ca- uptake (reaching a Ca/Sr-ratio of 0.49). On the contrary, in the presence of equimolar concentrations of Kryptofix (50–250 μM/l) there is an increasing preference of Ca versus Sr-uptake (Ca/Sr = 1.89).     

Is the salt tolerance of maize related to sodium exclusion? I. Preliminary screening of seven cultivars

Maize (Zea mays L.) plants in the early stage of development were treated with 80 mM sodium chloride (NaCl) with or without supplemental calcium (Ca²⁺) (8.75 mM) for a seven day period. The effects of salinity on dry matter production and shoot and root concentrations of sodium (Na⁺), Ca²⁺, and potassium (K⁺) were measured for seven Pioneer maize cultivars. Salinity significantly reduced total dry weight, leaf area, and shoot and root dry weight below control levels. For all seven cultivars, Na⁺concentrations were reduced and leaf area was significantly increased by supplementing salinized nutrient solutions with 8.75 mM calcium chloride (CaCl₂). The two cultivars with the lowest shoot and root Na⁺ concentrations under NaCl‐salinity showed the greatest increases in total, shoot and root dry weights with the addition of supplemental Ca. Shoot fresh weight/dry weight ratios for all cultivars were decreased significantly by both salinity treatments, but supplemental Ca²⁺ increased the ratio relative to salinity treatments without supplemental Ca. Root fresh weight/dry weight ratios were decreased only by salinity treatments with supplemental Ca. With NaCl‐salinity, cultivars which had lower shoot and root Na⁺ concentrations were found to be more salt sensitive and had significantly lower amounts of dry matter production than those cultivars which had higher shoot and root Na⁺ concentrations. It was concluded that Na⁺ exclusion from the shoot was not correlated with and was an unreliable indicator of salt tolerance for maize.     

Assessing the Toxic Effects of Nickel,Cadmium and EDTA on Growth of the Plant Growth-Promoting Rhizobacterium <Emphasis Type="Italic">Pseudomonas brassicacearum</Emphasis>

Plant growth-promoting rhizobacteria (PGPR) play an important role in the biodegradation of natural and xenobiotic organic compounds in soil. They can also alter heavy metal bioavailability and contribute to phytoremediation in the presence or absence of synthetic metal chelating agents. In this study, the inhibitory effect of Cd²⁺ and Ni²⁺ at different concentrations of Ca²⁺ and Mg²⁺, and the influence of the widely used chelator EDTA on growth of the PGPR Pseudomonas brassicacearum in a mineral salt medium with a mixture of four main plant exudates (glucose, fructose, citrate, succinate) was investigated. Therefore, the bacteriostatic effect of Cd²⁺, Ni²⁺ and EDTA on the maximum specific growth rate and the determination of EC50 values was used to quantify inhibitory impact. At high concentrations of Ca²⁺ (800 μmol L^-1) and Mg²⁺ (1,250 μmol L^-1), only a small inhibitory effect of Cd²⁺ and Ni²⁺ on growth of P. brassicacearum was observed (EC50 Cd²⁺, 18,849 ± 80 μmol L⁻¹; EC50 Ni²⁺, 3,578 ± 1,002 μmol L⁻¹). The inhibition was much greater at low concentrations of Ca²⁺ (25 μmol L⁻¹) and Mg²⁺ (100 μmol L⁻¹) (EC50 Cd²⁺, 85 ± 0.5 μmol L⁻¹ and EC Ni²⁺, 62 ± 1.8 μmol L⁻¹). For the chosen model system, a competitive effect of the ions Cd²⁺ and Ca²⁺ on the one hand and Ni²⁺ and Mg²⁺ on the other hand can be deduced. However, the toxicity of both, Cd²⁺ and Ni²⁺, could be significantly reduced by addition of EDTA, but if this chelating agent was added in stoichiometric excess to the cations, it also exhibited an inhibitory effect on growth of P. brassicacearum.     

Comparison of ammonium fertilizers,EDTA, and NTA on enhancing the uptake of cadmium by an energy plant,Napier grass (<Emphasis Type="Italic">Pennisetum purpureum</Emphasis> Schumach)

Purpose

The aim of this study was to quantify the effect of enhanced agronomic practices on cadmium (Cd) accumulation in the high-biomass energy plant Napier grass (Pennisetum purpureum Schumach).

Materials and methods

Potted-plant experiments were performed to investigate the effects of ammonium fertilizers and chelating agents, alone or in combination, on the growth, accumulation of Cd, and phytoextraction efficiency of P. purpureum on Cd-contaminated soil. The fertilizers included ammonium nitrate, ammonium sulfate, and ammonium chloride. The chelating agents included ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA).

Results and discussion

The addition of ammonium fertilizers and chelating agents generally stimulated growth of P. purpureum, and the shoots accounted for 90.1–94.1% of the total biomass. The concentrations of Cd in different parts of P. purpureum plants were in the order root > leaf > stem. Ammonium chloride alone showed effectiveness in increasing root and shoot Cd concentrations compared to other amendments alone. Both EDTA alone and NTA alone significantly decreased root Cd concentration and increased shoot Cd concentration, while EDTA alone was more efficient on shoot and total Cd accumulation than that by NTA alone. The total accumulation of Cd in P. purpureum ranged from 1.10 to 2.05 mg per plant with 47.3–73.5% of Cd accumulation concentrated in shoots. The results indicate that P. purpureum can remove more Cd through phytoextraction than that by other hyperaccumulators.

Conclusions

Ammonium chloride led to the highest total Cd accumulation. Ammonium chloride applied alone or in combination with either EDTA or NTA resulted in the most effective agronomic approaches for P. purpureum phytoextraction of soil Cd.

     

Arbuscular mycorrhizal fungus and rhizobacteria affect the physiology and performance of Sulla coronaria plants subjected to salt stress by mitigation of ionic imbalance

Salt stress has become a major menace to plant growth and productivity. The main goal of this study was to investigate the effect of inoculation with the arbuscular mycorrhizal fungi (AMF; Rhizophagus intraradices) in combination or not with plant growth‐promoting rhizobacteria (PGPR; Pseudomonas sp. (Ps) and Bacillus subtilis) on the establishment and growth of Sulla coronaria plants under saline conditions. Pot experiments were conducted in a greenhouse and S. coronaria seedlings were stressed with NaCl (100 mM) for 4 weeks. Plant biomass, mineral nutrition of shoots and activities of rhizosphere soil enzymes were assessed. Salt stress significantly reduced plant growth while increasing sodium accumulation and electrolyte leakage from leaves. However, inoculation with AMF, whether alone or combined with the PGPR Pseudomonas sp. alleviated the salt‐induced reduction of dry weight. Inoculation with only AMF increased shoot nutrient concentrations resulting in higher K⁺: Na⁺, Ca²⁺: Na⁺, and Ca²⁺: Mg²⁺ ratios compared to the non‐inoculated plants under saline conditions. The co‐inoculation with AMF and Pseudomonas sp. under saline conditions lowered shoot sodium accumulation, electrolyte leakage and malondialdehyde (MDA) levels compared to non‐inoculated plants and plants inoculated only with AMF. The findings strongly suggest that inoculation with AMF alone or co‐inoculation with AMF and Pseudomonas sp. can alleviate salt stress of plants likely through mitigation of NaCl‐induced ionic imbalance, thereby improving the nutrient profile.     

EFFECT OF ROOTSTOCK ON SALT TOLERANCE OF LOQUAT: GROWTH AND MINERAL COMPOSITION

The salinity tolerance of loquat grafted onto anger or onto loquat was studied. The plants were irrigated using solutions containing 5, 25, 35, 50, or 70 mM sodium chloride (NaCl) for five months. Different parameters of vegetative growth were studied, all of them showing that plants grafted onto loquat are much less salinity-tolerant than those grafted onto anger. Thus, the concentration of NaCl that produced a growth reduction of 50% (C₅₀) for the growth parameters of the shoot was around 35 mM for loquat plants grafted onto loquat. With the NaCl levels employed, loquat-anger plants did not reach the C₅₀. Lower chloride (Cl^?) and sodium (Na⁺) uptake, higher potassium (K⁺)-Na⁺ selectivity and a lower reduction in the leaf magnesium (Mg²⁺) concentration for the loquat-anger combination can explain the higher salinity tolerance compared to loquat-loquat.     

Uptake of Zn and Fe by wheat (Triticum aestivum var. Greina) and transfer to the grains in the presence of chelating agents (ethylenediaminedisuccinic acid and ethylenediaminetetraacetic acid)

A way to decrease iron and zinc deficiency in humans is to biofortify foods by increasing the bioavailable contents in these elements. The aim of this work was to study if chelating agents could be used to increase the capture of Fe and Zn by wheat grains. Zn and/or Fe in combination with the chelating agents ethylenediaminedisuccinic acid (EDDS) or ethylenediaminetetraacetic acid (EDTA) were added at various times (i.e., at flower head formation, anthesis, and postanthesis) to spring wheat ( Triticum aestivum var. Greina) grown in nutrient solution. Treatments lasted for 2 weeks, and the plants were harvested at grain maturity. The shoots of treated plants accumulated higher Zn and/or Fe concentrations than untreated plants, depending on the treatment. The plants also accumulated significant concentrations of EDDS or EDTA in their shoots. Elevated Zn and Fe concentrations in the shoots did in most cases not lead to significantly higher Zn and Fe concentrations in the grains. The grains of plants treated with EDDS during flower head formation accumulated elevated Fe and Zn concentrations but at the cost of a reduction in yield. The control plants transferred higher percentages of Fe and Zn from the shoot into the grain than the treated plants. This indicates that EDTA and EDDS inhibited in most cases the translocation of Fe and Zn from the shoots into the grains. The amounts of EDDS and EDTA found in the grains of treated plants were very small. This indicates that there was little transfer of the chelates into the symplast and that the apoplastic pathway, which is important for the transport of chelants into the shoots, is efficiently blocked between shoots and seeds.     

The Remobilization of Metals from Iron Oxides and Sediments by Metal-EDTA Complexes

Synthetic chelating agents such as EDTA form strong complexes with heavy metals and therefore have the potential to remobilize metals from sediments and aquifers. In natural waters EDTA is present almost exclusively in the form of metal-complexes. Therefore, remobilization of metals is always a metal-metal-EDTA exchange reaction. We have investigated, to our knowledge for the first time, the remobilization of metals from the surface of synthetic iron oxides and from a river sediment by different metal-EDTA complexes. The metals are exchanged as follows:MeEDTA_dissolved + Me^ast _adsorbed Me^astEDTA_dissolved + Me_adsorbed The order of the remobilization rate of Zn²⁺ from goethite is CaEDTA > Fe(III)EDTA, reflecting the slow exchange reaction of Fe(III)EDTA. For the remobilization of Pb²⁺ from goethite, the rate was found to be Fe(III)EDTA > CaEDTA > ZnEDTA. Here, Fe(III)EDTA has surprisingly the fastest exchange rate. Only very limited remobilization of Pb²⁺ is possible from hydrous ferric oxide at pH 8 due to the very strong adsorption of Pb²⁺. The order of remobilization of Zn²⁺ from a natural river sediment was found to be CaEDTA > CuEDTA > Fe(III)EDTA. The remobilization rate of Zn²⁺ with Fe(III)EDTA is only 12% of the rate with CaEDTA, illustrating the importance of EDTA speciation for assessing remobilization.     

Effects of Acid Mist and Ascorbic Acid Treatment on the Growth,Stability of Leaf Membranes,Chlorophyll Content and Some Mineral Elements of Carthamus tinctorius,the Safflower

Safflower shoots were sprayed with either HNO₃,HCl and H₂SO₄ acid solutions of pH 2.0 ordistilled water as a control and then sprayed with 0and 100 mg L^-1 ascorbic acid solutions. In theabsence of ascorbic acid, membranes of leaf discsexcised from acid misted plants were more injured bydehydration (40% polyethylene glycol, P.E.G.) andheat (51 °C) stress than those taken fromunmisted plants. Safflower plants sprayed with HCl andH₂SO₄ solutions had lower contents ofchlorophyll (Chl.), soluble sugars (S.S.),hydrolysable carbohydrates (H.C.), soluble proteins(S.P.); total free amino acids (T.A.A.) and producedless biomass in their shoot and root systems than theunacidified control. The reverse held true in theplants received HNO₃ solution. Proline contentincreased with exposure to an HCl acid mist of pH 2.0.An acid spray of pH 2.0 did not affect shoot Na⁺,K⁺ and Mg²⁺ content but reduced theircontents in the root. Shoot and root Ca²⁺contents were substantially lower in acid sprayedplants than in the unsprayed analogues. Ascorbic acidtreatment counteracted the deleterious effects of acidmist on the parameters tested, effectively protectingthe plant membranes from dehydration and heat stressinjury. Ascorbic acid protection was more pronouncedin plants that received HCl solution (e.g. chlorophyllcontent was about three-fold higher than that ofascorbic acid untreated analogues) in contrast toeither HNO₃ or H₂SO₄ treated plants.The effects of single factors, acid mist (pH),ascorbic acid (A.A.) and their interaction (pH × A.A)on the parameters tested were statisticallysignificant. The coefficient of determination(η²) indicated that: (1) acid mist (pH) hada dominant role in affecting the stability of leafmembrane to dehydration stress, Chl content, shootlength and dry mass production, shoot S.P. and H.C.,and root S.S., S.P., T.A.A., Ca²⁺, and Mg²⁺contents. (2) The effect of ascorbic acid (A.A.) wasdominant for shoot Na⁺, K⁺, Ca²⁺ andproline contents as well as for root H.C. (3) Theshare of pH × AA. interaction was dominant for thestability of leaf membrane to heat stress, root dryweight, shoot S.S., T.A.A. and root Na⁺ content.(4) The role of pH and A.A. was equally dominant inaffecting root length.     

Potassium and nitrogen effects on carbohydrate and protein metabolism in alfalfa roots

An investigation was conducted to determine the effect of potassium (K) nutrition on alfalfa (Medicago sativa L.) growth and metabolism of root total nonstructural carbohydrates (TNC) and proteins, and to study whether nitrogen (N) fertilization overcomes N deficiency and low root protein concentrations caused by K deficiency. In Experiment 1, nodulated alfalfa plants were grown in plastic pots containing washed quartz sand and provided minus‐N Hoagland's solution containing 0, 0.6, or 6.0 mM K. Shoot and root K concentrations increased with increasing solution K. Root N concentrations were higher in plants receiving 6.0 mM K than in plants receiving 0.6 or 0 mM K, but shoot N concentrations were similar for all treatments. Plant persistence, shoots per plant, and shoot mass increased as solution K levels increased. Root starch concentration and utilization were positively associated with K nutrition. Total amylase activity was higher, but endoamylase activity was lower in roots of plants receiving 6.0 mM K compared to plants receiving 0.6 or 0 mM K. Root soluble protein concentrations were significantly higher in plants receiving 6.0 mM K than in plants receiving 0 or 0.6 mM K. In Experiment 2, plants were supplied with Hoagland's solution containing 10 mM N as ammonium (NH₄ ⁺) or nitrate (NO₃) with 0,3, or 6.0 mM K. The addition of N increased root N concentrations only in plants receiving 0 mM K. Plant persistence was reduced by NH₄ ⁺ application, especially in plants receiving 0 or 3 mM K. Root starch concentrations were markedly reduced in plants receiving NH₄ ⁺ at all K levels. The addition of NO₃ ^‐ had little effect on alfalfa root carbohydrate and protein metabolism and subsequent shoot growth. Potassium deficiency reduced starch and protein concentrations in roots; factors that were associated with poor persistence and slow shoot regrowth of alfalfa.     

Effects of NaCl and silicon on ion distribution in the roots,shoots and leaves of two alfalfa cultivars with different salt tolerance

Abstract

The effects of exogenous NaCl and silicon on ion distribution were investigated in two alfalfa (Medicago sativa. L.) cultivars: the high salt tolerant Zhongmu No. 1 and the low salt tolerant Defor. The cultivars were grown in a hydroponic system with a control (that had neither NaCl nor Si added), a Si treatment (1 mmol L^?1 Si), a NaCl treatment (120 mmol L^?1 NaCl), and a Si and NaCl treatment (120 mmol L^?1 NaCl + 1 mmol L^?1 Si). After 15 days of the NaCl and Si treatments, four plants of the cultivars were removed and divided into root, shoot and leaf parts for Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Mn²⁺, Cu²⁺ and Zn²⁺ content measurements. Compared with the NaCl treatment, the added Si significantly decreased Na⁺ content in the roots, but notably increased K⁺ contents in the shoots and leaves of the high salt tolerant Zhongmu No.1 cultivar. Applying Si to both cultivars under NaCl stress did not significantly affect the Fe³⁺, Mg²⁺ and Zn²⁺ contents in the roots, shoots and leaves of Defor and the roots and shoots of Zhongmu No.1, but increased the Ca²⁺ content in the roots of Zhongmu No.1 and the Mn²⁺ contents in the shoots and leaves of both cultivars, while it decreased the Ca²⁺ and Cu²⁺ contents of the shoots and leaves of both cultivars under salt stress. Salt stress decreased the K⁺, Ca²⁺, Mg²⁺ and Cu²⁺ contents in plants, but significantly increased Zn²⁺ content in the roots, shoots and leaves and Mn²⁺ content in the shoots of both cultivars when Si was not applied. Thus, salt affects not only the macronutrient distribution but also the micronutrient distribution in alfalfa plants, while silicon could alter the distributions of Na⁺ and some trophic ions in the roots, shoots and leaves of plants to improve the salt tolerance.     

Growth Responses and Nitrogen-15 Absorption of Desert Saltgrass Under Salt Stress

Abstract

Saltgrass [Distichlis spicata (L.) Greene var. stricta (Gray) Beetle], accession WA-12, collected from a salt playa in Wilcox, AZ, was studied in a greenhouse to evaluate its growth responses in terms of shoot and root lengths, shoot dry-matter yield, and nitrogen (N) (regular and ¹⁵N) absorption rates under control and salt (sodium chloride, NaCl) stress conditions. Plants were grown under a control (no salt) and three levels of salt stress (100, 200, and 400 mM NaCl, equivalent to 5850, 11700, and 23400 mg L^{? 1} sodium chloride, respectively), using Hoagland solution in a hydroponics system. Ammonium sulfate [(¹⁵NH₄)₂SO₄], 53% ¹⁵N (atom percent ¹⁵N) was used to enrich the plants. Plant shoots were harvested weekly, oven-dried at 60°C, and the dry weights measured. At each harvest, both shoot and root lengths were also measured. During the last harvest, plant roots were also harvested and oven-dried, and dry weights were determined and recorded. All harvested plant materials were analyzed for total N and ¹⁵N. The results showed that shoot and root lengths decreased under increasing salinity levels. However, both shoot fresh and dry weights significantly increased at 200 mM NaCl salinity relative to the control or to the 400 mM NaCl level. Shoot succulence (fresh weight/dry weight) also increased from the control (no salt) to 200 mM NaCl, then declined. The root dry weights at both 200 mM and 400 mM NaCl salinity levels were significantly higher than under the control. Concentrations of both total-N and ¹⁵N in the shoots were higher in NaCl-treated plants relative to those under the control. Shoot total-N and ¹⁵N contents were highest in 200 mM NaCl-treated plants relative to those under the control and 400 mM salinity.     

Phytoextraction of heavy metal contaminated soils with Thlaspi goesingense and Amaranthus hybridus: Rhizosphere manipulation using EDTA and ammonium sulfate

Selection of appropriate plant species and rhizosphere manipulation to enhance metal uptake are considered key factors in the development of phytoextraction technologies. A pot trial was conducted with two contaminated soils to investigate the effect of EDTA and ammonium sulfate on the accumulation of heavy metals into shoots of the low‐biomass hyperaccumlator Thlaspi goesingense Hálácsy (Brassicaceae) and the high‐biomass non‐hyperaccumulating plant Amaranthus hybridus (Amaranthaceae). Upon application of 1 g EDTA (kg soil)^—1 metal extractability with 1 M NH₄NO₃ increased substantially, whereas the application of (NH₄)₂SO₄ was less effective. The EDTA treatment increased the heavy metal concentrations in both plant species, however, the difference to the control was larger for A. hybridus. EDTA enhanced shoot concentrations in A. hybridus grown on soil Arnoldstein from 32.7 mg kg^—1 to 1140 mg kg^—1 for Pb and from 3.80 mg kg^—1 to 10.3 mg kg^—1 for Cd. Cd concentrations in shoots of T. goesingense were also increased by EDTA application, however, a slight decrease was observed for Pb. T. goesingense accumulated 2840 mg Pb kg^—1 without any treatment. This is the first report of Pb hyperacumulation by T. goesingense. A decrease of shoot Pb concentration was observed in T. goesingense upon treatment with ammonium sulfate. Although metal concentrations in the shoots were rather large and significantly increased upon application of EDTA, plant growth and heavy metal removal were still too small to obtain reasonable extraction rates in soils heavily polluted by metals. It should be also noted that metal lability largely increased in EDTA‐treated soils and this lability persisted for several weeks after the application of the chelating agent, which is likely to be associated with the risk of groundwater contamination.     

Activation of soil pyrophosphatase by metal ions

Inorganic pyrophosphatase activity in three soils decreased when exchangeable and soluble metals were removed by leaching with in NH₄OAc (pH 8). The effect of added metal ions at various concentrations in the leached soils showed that, at certain concentrations, Ba²⁺, Ca²⁺, Co²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ promoted, K⁺ and Na⁺ had no effect, and Fc²⁺ and Cu²⁺ decreased pyrophosphatase activity. At high concentrations (>50 mM). Co²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ inhibited pyrophosphatase activity in two soils. The concentration of metal ion needed for optimum activity of pyrophosphatase varied among the soils. The efficiency of the metal ions at optimum concentrations (average percentage increase for three soils in parentheses) in promoting pyrophosphatase was Ca²⁺ (47) > Mg²⁺ (42) > Ba²⁺ = Co²⁺ (29) > Ni²⁺ (27) > Zn²⁺ (20) > Mn²⁺(16). Pyrophosphatase activity in two leached soils adjusted to 50, 75, 100 or 150 mM PPi and Ca²⁺ or Mg²⁺ concentrations from 0 to 250 mM was at an optimum when the metal ion: PPi ratio was 1:1. Soil pyrophosphatase in the presence of 200 mM CaCl₂ or MgCl₂ was protected against inactivation by heat (90 C for up to 30 min).