Zinc alleviates growth inhibition and oxidative stress caused by cadmium in rice

A hydroponic experiment with two rice cultivars differing in cadmium (Cd) tolerance was conducted to investigate the alleviating effect of zinc (Zn) on growth inhibition and oxidative stress caused by Cd. Treatments consisted of all combinations of two Zn concentrations (0.2 and 1 μM), three Cd concentrations (0, 1, and 5 μM), and two rice cultivars (Bing 97252, Cd‐tolerant; Xiushui 63, Cd‐sensitive). Cd toxicity caused a dramatic reduction in plant height and biomass, chlorophyll concentration and photosynthetic rate, and an increase in Cd concentration in both roots and shoots, malondialdehyde (MDA) concentration, and superoxide dismutase (SOD) and peroxidase (POD) activities in shoots. The response of all these parameters was much larger for Xiushui 63 than for Bing 97252. Addition of Zn to the medium solution alleviated Cd toxicity, which was reflected in a significant increase in plant height, biomass, chlorophyll concentration, and photosynthetic rate, and a marked decrease in MDA concentration and activity of anti‐oxidative enzymes. However, it was noted that Zn increased shoot Cd concentration at higher Cd supply, probably due to the enhancement of Cd translocation from roots to shoots. Therefore, further studies are necessary to determine the effect of Zn supply on Cd translocation from vegetative organs to grains or grain Cd accumulation before Zn fertilizer is applied to Cd‐contaminated soils to alleviate Cd toxicity in rice.     

Effects of Manganese Deficiency on Growth and Contents of Active Constituents of Glycyrrhiza uralensis Fisch.

To investigate effects of manganese (Mn) deficiency (0 μM L^–1) on concentrations of chlorophyll, superoxide dismutase (SOD) activity, biomass, and accumulations of active constituents in Glycyrrhiza uralensis Fisch., seedlings of 1-year-old G. uralensis were grown in a nutrient solution for 60 days. In this experiment, three concentrations of Mn were set up: 0 (–Mn), 7 μM L^–1, and 14 μM L^–1 Mn. The results showed that –Mn decreased the concentration of chlorophyll a with no significant differences in concentrations of chlorophyll b, total chlorophyll a + b, carotenoids, and chlorophyll a/b ratio. On days 45 and 60, SOD activity significantly decreased. However, dry weight of roots under –Mn showed no significant difference during the whole experiment. The accumulations of glycyrrhizic acid and liquiritin were significantly inhibited by Mn deficiency at different times. Thus results indicated that Mn deficiency could affect growth and contents of its secondary metabolites of G. uralensis.     

Amelioration of copper toxicity by iron on Spinach physiology

The effect of excess copper (Cu) on young spinach (Spinacia oleraced) as well as the role of iron (Fe) for amelioration of toxicity on growth and photosynthesis in Cu‐treated plants was evaluated. Plants treated with 160 μM Cu showed symptoms of heavy metal toxicity, while addition of Fe (40 μM) ameliorates to a certain extent toxic effects of Cu, due to antagonistic action between Cu and Fe. Root length and biomass revealed a lower decrease under Cu+Fe than under Cu treatment. Copper accumulation in plant tissues increased, while Fe, sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) declined under Cu treatment. The significant increase in chlorophyll fluorescence (F_o) under 160 μM Cu, possibly reflects the more severe damages suffered at the membrane level with respect to Cu+Fe treatment. Copper decreased the efficiency of excitation energy capture by PSH reaction centers and negatively affected the effective antenna size of PSH. Changes in the rate of carbon dioxide (CO₂) assimilation were associated with changes in both stomatal conductance (gs) and mesophyll capacity for photochemistry as well as with lower pigment content. Net CO₂ assimilation, transpiration rate, and stomatal conductance were reduced. These changes at PSII are characteristic of a saturation of photosynthetic metabolic activity. The results suggest a tight linkage between PSII activity and CO₂ fixation under Cu treatment. Amelioration of Cu toxicity was obvious under Fe application.     

Status of photosynthetic pigments,lipid peroxidation and anti-oxidative enzymes in Vigna mungo in presence of arsenic

The response to arsenic was evaluated for photosynthetic pigments, lipid peroxidation and anti-oxidative enzymes in black gram. Black gram (Vigna mungo) subjected to arsenic doses of 100 µM and 200 µM, showed increased amount of lipid peroxidation. Activity of peroxidase (POD) increased tremendously in arsenic treated Vigna leaves over control. Similarly, activities of enzymes like superoxide dismutase (SOD) and ascorbate peroxidase (APX) also increased with increase in arsenic. Analysis of native PAGE superoxide dismutase activity showed one manganese (Mn)-SOD and two copper/zinc (Cu/Zn)-SOD isoenzymes in black gram leaves, whose intensity increased especially at 200 µM arsenic treatment. However, activity of catalase (CAT) decreased with increase in concentrations of arsenic. This clearly indicates that except CAT, all studied antioxidative enzymes like SOD, POD and APX showed increased expression at arsenic treatments, which reflects their protective role against arsenic toxicity in black gram plants. Photosynthetic pigments like chlorophyll and carotenoids showed reduction with increasing concentrations of arsenic in treatment solutions.     

INFLUENCE OF SUCCINATE ON ZINC TOXICITY OF PEA PLANTS

The response of pea plants (Pisum sativum, cv. Citrine) to various zinc (Zn) concentrations (0.67 to 1000 μM Zn) in the presence and absence of succinate (200 μM Na-succinate) were investigated. Treatment of pea plants alone with excess of Zn reduced plant growth, chlorophyll content and induced alterations in the structure of the chloroplast, resulting mainly in decreased granal thylakoids. The photochemical activity of photosystem II estimated by the ratios F_v/F_m and F_v/F_o was less affected by Zn treatment. The presence of succinate lead to an increase in plant growth and chlorophyll content, improved chloroplast structure of and recovered photosystem II activity in Zn-treated plants. This stimulation was accompanied by an increased zinc root concentration and a decreased zinc shoot concentration. The higher root zinc concentration and decreased zinc translocation from root to shoot by succinate treatment suggest that succinate facilitates the formation of metal-succinate complexes in the roots and may play a role in zinc accumulation.These results provide indirect evidence for a possible role of succinate in Zn-resistance of plants.     

Supra‐optimal growth temperature exacerbates adverse effects of low Zn supply in wheat

Rising temperatures are a major threat to global wheat production, particularly when accompanied by other abiotic stressors such as mineral nutrient deficiencies. This study aimed to quantify the effects of supra‐optimal temperature on growth, photosynthetic performance, and antioxidative responses in bread wheat cultivars grown under varied zinc (Zn) supply. Two bread wheat cultivars (Triticum aestivum L., cvs. Lasani‐2008 and Faisalabad‐2008) with varied responsiveness to Zn supply and drought tolerance were cultured in nutrient solution with low (0.1 µM) or adequate (1.0 µM) Zn under optimal (25/20°C day/night) or supra‐optimal (36/28°C day/night) temperature regimes. Supra‐optimal temperature severely reduced root but not shoot biomass, whereas low Zn reduced shoot as well as root biomass. Shoot‐to‐root biomass ratio was reduced under low Zn but increased under supra‐optimal temperature. Supra‐optimal temperature inhibited root elongation and volume particularly in plants supplied with low Zn. In both cultivars, Zn efficiency index was reduced by supra‐optimal temperature, whereas heat tolerance index was reduced by low Zn supply. Supra‐optimal temperature decreased photosynthesis, quantum yield, and chlorophyll density in low‐Zn but not in adequate‐Zn plants. In comparison, low Zn decreased specific activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and increased glutathione reductase (GR), where supra‐optimal temperature increased SOD, decreased GR and did not change APX activity in leaves and roots. Moreover, supra‐optimal temperature severely reduced shoot Zn concentration and Zn uptake per plant specifically under adequate Zn supply. Overall, supra‐optimal temperature exacerbated adverse effects of low Zn supply, resulting in severe reductions in growth traits viz. shoot and root biomass, root length and volume, and consequently impeded Zn uptake, enhanced oxidative stress and impaired photosynthetic performance. Adequate Zn nutrition is crucial to prevent yield loss in wheat cultivated under supra‐optimal temperatures.     

Foliar application of zinc alleviates the heat stress of pakchoi (Brassica chinensis L.)

Abstract

Experiments were conducted to examine whether the foliar application of zinc (Zn) could mitigate the adverse effects of heat stress on pakchoi plants. Two varieties of pakchoi (Aikangqing and Wuyueman) were foliar applied with ZnSO₄·7H₂O (0%, 0.02%, 0.05%, 0.10%, 0.20%, 0.40%, 0.60%, and 0.80%), and then subjected to two temperature levels (22°C/16°C, day/night; 40°C/30°C, day/night). Heat stress decreased the net photosynthetic rate (P_n) (50.65% and 62.14% for Aikangqing and Wuyueman, respectively), chlorophyll content, chlorophyll fluorescence ratio (F_v/F_m), and effective quantum yield of PSII photochemistry (ΦPSII) of the leaves. Foliar application of ZnSO₄·7H₂O (0.02%–0.40%) effectively alleviated the heat stress in pakchoi by enhancing shoot Zn concentration, superoxide dismutase (SOD) activity, chlorophyll content, F_v/F_m, and ΦPSII. P_n increased by 12.61%–46.19% and 45.73%–119.01% in Aikangqing and Wuyueman compared with those without Zn treatments, respectively. Fuzzy comprehensive evaluation and the extreme model showed that Aikangqing and Wuyueman treated with 0.1218%–0.1220% ZnSO₄·7H₂O (approximately 0.004?M Zn²⁺) and 0.2178%–0.2744% ZnSO₄·7H₂O (approximately 0.008?M Zn²⁺) exhibited the most heat resistance, respectively. Furthermore, Zn (0.02%–0.80% ZnSO₄·7H₂O) application had no significant effect on most physicochemical parameters under normal temperature, which only increased shoot Zn and SOD. The results suggest that additional Zn would be required to fully protect plant growth from heat stress. Foliar application enhanced Zn concentration in leaves, thereby maintaining the SOD activity and membrane stability and protecting photosynthesis against heat damage.     

Effects of Nickel on Growth and Composition of Metal Micronutrients in Barley Plants Grown in Nutrient Solution

Abstract

A hydroponic experiment was conducted in a phytotron at pH 5.5 to study the effects of nickel (Ni) on the growth and composition of metal micronutrients, such as copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn), of barley (Hordeum vulgare L. cv. Minorimugi). Four Ni treatments were conducted (0, 1.0, 10, and 100 μM) for 14 d. Plants grown in 100 μM Ni showed typical visual symptoms of Ni toxicity such as chlorosis, necrosis of leaves, and browning of the root system, while other plants were free from any symptoms. Dry weights were the highest in plants grown in 1.0 μM Ni, with a corresponding increase in the chlorophyll index of the plants, suggesting that 1.0～10 μM Ni needs to be added to the nutrient solution for optimum growth of barley plants. The increase of Ni in the nutrient solutions increased the concentrations of Cu and Fe in roots, while a decrease was observed in shoots. The concentrations of Mn and Zn in shoots and roots of plants decreased with increasing Ni supply in the nutrient solution. Shoot concentrations of Cu, Fe, Mn, and Zn in plants grown at 100 μ M Ni were below the critical levels for deficiency. Plants grown at 1.0 μ M Ni accumulated higher amounts of Cu, Fe, Mn and Zn, indicating that nutrient accumulation in plants was more influenced by dry weights than by nutrient concentrations. The translocation of Cu and Fe from roots to shoots was repressed, while that of Mn and Zn was not repressed with increasing Ni concentration in the nutrient solution.     

Effect of pH on growth and uptake of copper by Swingle citrumelo seedlings 1

Copper (Cu) phytotoxicity is closely related to pH and Cu activity in solution. The effect of pH on growth and uptake of Cu by Swingle citrumelo rootstock seedlings were investigated in solution culture with varying Cu activities. Copper activities of either 0.05, 0.5, 5, and 10 μM at pH 5 and 6 were maintained by adding copper sulfate (CuSO₄) to the hydroponic solution based on the calculation by GEOCHEM computer program. After 42 days, root and shoot growth decreased significantly in solutions where Cu activities were greater than 0.5 μM. The concentration of Cu in roots are greater and the dry weights of roots and shoots were less in solutions at pH 6 than those at pH 5. A 200‐fold increase in Cu activity in solution resulted in a corresponding increase in concentration of Cu in the root but not in the shoot.     

Zinc hyperaccumulation in Thlaspi caerulescens. II. Influence on organic acids

The influence of different zinc (Zn) concentrations (1.5 to 1500 μM) on organic acid levels in roots and shoots of the Zn‐hyperaccumulator plant Thlaspi caerulescens was investigated. In shoots, malate was the most abundant organic acid (164 to 248 μmol/g f.w.), followed by citrate, succinate, and oxalate. A significant correlation between soluble Zn and both malate and oxalate was observed in shoots, but not in roots. In shoots, a significant correlation between inorganic cation equivalents and organic acid anion equivalents was found. These observations and the finding, that organic acid concentrations were high even under suboptimal Zn supply (1.5 μM) suggest that in T. caerulescens the high organic acid concentration in shoots is a constitutive property. The variation of the organic acid concentrations seem to be a consequence of the cation‐anion balance rather than a specific Zn tolerance mechanism. The constitutively high organic acid concentration may be responsible for the high Zn and iron (Fe) tissue concentrations required for optimum growth in T. caerulescens.     

Diffusive flux of cationic micronutrients in two Oxisols as affected by low‐molecular‐weight organic acids and cover‐crop residue

Low‐molecular‐weight organic acids with one or more carboxylic groups are ubiquitous. In soils, they can originate from leaching of plants, litter decomposition, plant‐roots exudation, and microbial activity. Their presence in the soil may favor the formation of soluble organo‐metallic complexes that improve the transport of Zn, Cu, Fe, and Mn to plant‐root surfaces via diffusion. The current study sought to determine if some of the organic acids (OA) in soils and a cover‐crop residue influence the diffusive flux (DF) of Zn, Cu, Mn, and Fe. Two OA were added to two Oxisols (Typic Haplustox): a clayey Dark Red Latosol (DRL) and a sandy‐loam Red Yellow Latosol (RYL). Acetic and citric acid were added to achieve concentrations of 0, 250, 500, 1000, and 2000 mmol (m³ soil)^–1. The effect of adding plant material (pearl millet) on the soil DF of the cationic micronutrients was also determined. Soil diffusive flux was evaluated by incubating positively charged and negatively charged exchange‐resin membranes with the soil in PVC diffusion chambers for 15 d. Desorption of Zn, Cu, Fe, Mn, and OA from the resins was performed with 0.5 mol l^–1 HCl. The results demonstrated that the DF of the cationic micronutrients increased with the addition of organic acid. The DF of Zn and Mn occurred mostly towards the cationic resin, whereas the diffusive flux of Cu and Fe occurred mostly towards the anionic resin. Apparently, the dissolution of oxides and/or complexation of micronutrients adsorbed to the solid phase or in the soil solution contributed to the obtained results. Citric acid was more efficient than acetic acid in maintaining a larger DF value for Zn, Cu, and Fe. The addition of millet plant material to the soil increased the DF in the following order: Mn > Cu > Fe > Zn; Mn moved towards the cationic resin, and the other micronutrients moved towards the anionic resin. These findings suggest that organic compounds play an important role in the short‐distance transport of cationic micronutrients in highly weathered soils.     

Interelemental relationships in the soil and plant tissue and photosynthesis of field‐cultivated wheat growing in naturally enriched copper soils

Several interelemental relationships have been examined in field‐cultivated wheat (Triticum aestivum L. cv Vergina) growing on naturally enriched copper (Cu) soils. Mean soil Cu concentration per site ranged from 103–394 μg.g^‐1 dry weight (DW). Interrelationships between Cu, iron (Fe), calcium (Ca), potassium (K), zinc (Zn), lead (Pb), and magnesium (Mg) concentrations in the soil and plant tissue (roots, stems, and leaves) were examined using Principle Components Analysis. Soil samples were clustered according to collection site and were primarily differentiated according to their Cu concentrations. Soil Cu concentrations were positively correlated with Zn, Ca, Fe, and K in the soil, with Cu, K, and Ca in the roots, and Cu and Fe in the leaves and negatively correlated with Fe in the roots. The increase in Cu in the roots and leaves was positively correlated with increases in K and Ca in the roots and Fe and Ca in the leaves, but negatively with Fe in the roots. Increases in leaf Ca concentrations were correlated with increases in Mg and decreases in Zn concentrations in the leaf. Plants growing in soil with high Cu concentration exhibited toxicity symptoms with reduced height, decreased total leaf area and lower chlorophyll concentrations. Photosynthesis expressed per unit leaf area was not affected by increasing Cu concentrations in the soil or plant tissue.     

Base cations ameliorate Zn toxicity but not Cu toxicity in sugar beet (Beta vulgaris)

Seedlings of sugar beet (Beta vulgaris) were grown in nutrient solutions containing a range of Cu and Zn concentrations. Based on measurements of shoot and root length and dry weight, copper was found to be already toxic at 10 μM, while Zn became toxic at 100 μM. At Cu and Zn levels found to induce a similar level of growth inhibiton, the influence of increasing the supply of K, Ca and Mg was investigated. Increasing the concentration of both Ca and Mg in the nutrient solution attenuated the degree of inhibition of root growth by Zn, but not Cu. Potassium did not affect the toxicity of either Cu or Zn. An increase in Ca decreased the level of both Cu and Zn in roots. Magnesium ameliorated the toxicity effects of Zn without effecting the Zn concentration in the roots. Treatment with Zn significantly decreased the concentration of Mg in the roots. An increased supply of Mg lowered the percentage decrease in root Mg concentration due to Zn toxicity. The maintenance of an adequate Mg level in the roots may be critical to prevent Zn induced inhibition of root growth.     

Synergistic trace metal effects in plants

Abstract

An experiment was conducted in Yolo loam soil with bush beans (Phaseolus vulgaris L. C.V. Improved Tendergreen) with single and combination treatments of moderately high levels of Cd, Li, Cu, and Ni to test whether or not effects could be additive or synergistic. Copper and Ni together were more toxic than either alone. Copper, Ni, and Cd were more toxic together than any one alone. These effects were probably additive and may be related to a 0.2 pH change caused by Cu which increased uptake of Ni and Mn. Synergistic effects were observed in the Cd and Ni concentrations, especially in the stems of the plants. Because of these interactions, the effects were then tested in solution culture. In solution culture with bush beans Cu and Ni when applied together had synergistic effects on plant concentrations of P, Zn, and Fe (all were decreased) and on the Ni concentration in roots. Also, in solution culture with (2.5 × 10^‐5 M) Zn, Cu, and Cd added singly, in pairs, and together, Zn and Cu additively decreased Cd concentrations in roots. Synergistic effects on yield depressions were observed in solution culture for 5 × 10^‐5 M Zn + 3 × 10^‐5 M Cu+ 2 x10^‐5 M Ni. An additive effect on yield depression was observed for 2 × 10^‐4 MCd + 2 × 10^‐5 M Ni. There were many complex interactions among the trace metal concentrations in these plants.     

Toxicity of copper and zinc in seedlings of Mung bean and inducing accumulation of polyamine

A solution culture was conducted to investigate the effects of copper (Cu) and zinc (Zn) toxicity on growth of mung bean (Phaseolus aures Roxb. cv VC‐3762) and accumulation of polyamine. Eight‐day‐old seedlings were grown in diluted nutrient solution with different concentrations of Cu and Zn for 6 days. Results showed that elongation of epicotyl and fresh weight of plants were decreased by 10 μM Cu and 100 μM Zn significantly compared to control (0.03 μMCu and 0.1 μMZn). Accumulation of polyamine, especially putrescine (Put) was found in the epicotyl of mung bean seedlings. Addition of 5 mM calcium (Ca) into nutrient solution improved the growth of 10 μM Cu‐treated seedling, and decreased the concentration of Put and increased concentrations of spermine and spermidine in epicotyl of plants. Moreover, supplying Put did not increase tolerance of plant to Cu or Zn. It was suggested that Put accumulation resulting from toxicity of Cu and Zn might merely be a symptom of stress injury.     

Compensatory root growth in winter wheat: Effects of copper exposure on root geometry and nutrient distribution

Plants of winter wheat (Triticum aestivum L. cv. Starke II) were grown for seven days in split‐root chambers containing nutrient solutions with various copper chloride (CuCl₂) concentrations [0.5/0.5 (controls), 0.5/2, 0.5/5, 0.5/7 and 0.5/10 μM]. At harvest (day 11), shoot dry weights were about the same in the different copper (Cu) treatments. Dry weights of the root parts exposed to 2–10 μM Cu (Cu‐fed) decreased while they increased for the control roots. A Cu exposure of 2–10 μM severely retarded lateral root initiation and average lateral root length. Average seminal root length was also reduced. The control roots compensated for the retarded growth of the Cu‐fed roots by increasing chiefly in lateral root number, but their average length remained similiar. Phosphorus (P) concentration decreased gradually in all determined plant parts (shoots, Cu‐control and Cu‐fed roots) with increased external Cu concentration. The potassium (K) concentration in the shoots was similarly affected, but it did not decrease in the Cu‐fed roots until the external Cu concentration reached 10 μM. The Cu concentration in the Cu‐fed roots increased proportionally to the external Cu concentration, but Cu was not exported to the other plant parts. The reasons for changes in root geometry and nutrient balance are discussed.     

Effects of excess aluminum on mineral uptake in mycorrhizal sorghum

Soil acidity is often associated with toxic aluminum (Al), and mineral uptake usually decreases in plants grown with excess Al. This study was conducted to evaluate the effects of Al (0, 35, 70, and 105 μM) on Al, phsophorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn,) and copper (Cu) uptake in shoots and roots of sorghum [Sorghum bicolor (L.) Moench, cv. SC283] colonized with the vesicular‐arbuscular mycorrhizal (VAM) fungi isolates Glomus intraradices UT143–2 (UT143) and Glomus etunicatum UT316A‐2 (UT316) and grown in sand (pH 4.8). Mycorrhizal (+VAM) plants had higher shoot and root dry matter (DM) than nonmycorrhizal (‐VAM) plants. The VAM treatment had significant effects on shoot concentrations of P, K, Ca, Fe, Mn, and Zn; shoot contents of P, S, K, Ca, Mg, Fe, Mn, Zn, and Cu; root concentrations of P, S, K, Ca, Mn, Zn, and Cu; and root contents of Al, P, S, K, Ca, Mg, Fe, Mn, Zn, and Cu. The VAM effects on nutrient concentrations and contents and DM generally followed the sequence of UT316 > UT143 > ‐VAM. The VAM isolate UT143 particularly enhanced Zn uptake, and both VAM isolates enhanced uptake of P and Cu in shoots and roots, and various other nutrients in shoots or roots.     

Effects of excess manganese on mineral uptake in mycorrhizal sorghum

Associations between vesicular‐arbuscular mycorrhizal (VAM) fungi and manganese (Mn) nutrition/toxicity are not clear. This study was conducted to determine the effects of excess levels of Mn on mineral nutrient uptake in shoots and roots of mycorrhizal (+VAM) and non‐mycorrhizal (‐VAM) sorghum [Sorghum bicolor (L) Moench, cv. NB9040]. Plants colonized with and without two VAM isolates [Glomus intraradices UT143–2 (UT1 43) and Gl. etunicatum UT316A‐2 (UT316)] were grown in sand irrigated with nutrient solution at pH 4.8 containing 0, 270, 540, and 1080 μM of added Mn (as manganese chloride) above the basal solution (18 μM). Shoot and root dry matter followed the sequence of UT316 > UT143 > ‐VAM, and shoots had greater differences than roots. Shoot and root concentrations and contents of Mn, phosphorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), and copper (Cu were determined. The +VAM plants generally had higher mineral nutrient concentrations and contents than ‐VAM plants, although ‐VAM plants had higher concentrations and contents of some minerals than +VAM plants at some Mn levels. Plants colonized with UT143 had higher concentrations of shoot P, Ca, Zn, and Cu and higher root Mg, Zn, and Cu than UT316 colonized plants, while UT316 colonized plants had higher shoot and root K concentrations than UT143 colonized plants. These results showed that VAM isolates differ in enhancement of mineral nutrient uptake by sorghum.     

铜对小白菜的毒性效应及其生态健康指标

以小白菜地上部分及根系重量、叶绿素值(SPAD值)以及与抗逆性有关的丙二醛(MDA)、超氧化物歧化酶活性(SOD)、脯氨酸含量等作为毒性指标,研究了04～00.mg/kg外源铜对青紫泥小白菜生长的影响,并应用“生态剂量”概念计算青紫泥栽培小白菜的铜污染安全指标及食品卫生指标。结果表明,低浓度铜(200.mg/kg)则造成小白菜减产,400.mg/kg的外源铜使小白菜减产84%;铜污染使根系重量下降表现出与地上部分同样的趋势。SPAD值随铜污染浓度的增加而呈线性下降;铜污染浓度低于100.mg/kg有促进根体积、根长度、根表面积增加的趋势,但超过200.mg/kg的铜浓度则显著降低根长、根体积和根表面积。在与重金属污染引起的抗逆性有关的生理生化指标中,脯氨酸最为敏感,铜浓度小于50.mg/kg或大于200.mg/kg都能显著影响脯氨酸含量及SOD活性;与脯氨酸的变化一样,高浓度铜增加了MDA含量;青紫泥铜污染的临界指标为171.mg/kg。     

Water‐stress mitigation by selenium in Trifolium repens L.

This study was designed to examine whether external selenium (Se) may improve the tolerance of Trifolium repens L. to polyethylene glycol (PEG)–induced water deficit, and to determine the physiological mechanisms of the possibly enhanced tolerance. Trifolium repens seedlings were subjected to PEG‐induced water deficit alone or combined with 5 μM Na₂SeO₄ for 24, 48, and 72 h. During the experimental period, the fresh weight (FW) of T. repens seedlings and the relative water content (RWC) of the leaves decreased gradually, and the chlorophyll concentration increased after 24 and 48 h, but decreased after 72 h. The PEG+Se‐treated plants had higher FW, RWC, and chlorophyll concentration than the PEG‐treated plants. Smaller amounts of thiobarbituric acid‐reactive substances (TBARS) and H₂O₂ accumulated in PEG+Se‐treated plants than in plants treated only with PEG. The activity of superoxide dismutase (SOD) increased gradually during the water‐deficit period, and Se application promoted SOD activity further. Catalase (CAT) activity remained unchanged after 24 and 48 h and insignificantly increased after 72 h of water deficit, whereas ascorbate peroxidase (APOX) activity increased linearly and glutathione reductase (GR) activity increased slightly over the course of treatment. Whereas the Se application exhibited no effect on the CAT activity, seedlings treated with PEG+Se had higher APOX activity during the whole experimental period and a higher GR activity after 48 and 72 h than PEG‐treated plants. These results suggest that exogenous Se treatment enhanced T. repens tolerance to PEG‐induced water deficit, and this enhancement was related to alleviation of lipid peroxidation and activation of antioxidant enzymes such as SOD, APOX, and GR.