Sulfur Alleviates Growth Inhibition and Oxidative Stress Caused by Cadmium Toxicity in Rice

A hydroponic experiment was conducted to investigate the effect of sulfur (S) on growth inhibition and oxidative stress caused by Cd²⁺ toxicity, using two rice cultivars with different grain Cd²⁺ content. Treatments consisted of factorial arrangement of three S levels (0.2, 0.4, and 0.8 mmol), two cadmium (Cd) levels (0 and 1 μ mol), and two rice cultivars (‘Bing 97252,’ a cultivar with low grain Cd²⁺ content, and ‘Xiushui 63,’ a cultivar with high grain Cd²⁺ content). The results showed that Cd²⁺ addition in the medium generally increased Cd²⁺ and malondialdehyde (MDA) content in both roots and shoots; the increases were more pronounced in ‘Xuishui 63’ than in ‘Bing 97252.’ Dramatic reductions in growth parameters, including plant height, root and shoot weight, tillers per plant, chlorophyll content, and net photosynthetic rate were found in the plants exposed to Cd stress relative to the plants without Cd²⁺ treatment. ‘Xiushui 63’ showed more sensitivity than ‘Bing 97252’ under Cd²⁺ exposure. In comparison with the lower S level (0.2 mmol), the higher S levels (0.4 and 0.6 mmol) helped alleviate Cd toxicity, characterized by a significant increase in growth parameters, and a decrease in Cd²⁺ and MDA content in both roots and shoots. In addition, superoxide dismutase (SOD) activity in the plants varied among tissues, cultivars, and Cd treatments. High Cd²⁺ and MDA content was consistently accompanied by higher SOD activity, and higher S levels caused a marked increase in glutathione content and a reduction in SOD activity, indicating a positive effect of S in alleviating oxidative stress.     

Alleviation effects of calcium and potassium on cadmium rhizotoxicity and absorption by soybean and wheat roots

The objectives of the present study were to investigate the root responses of soybean (Glycine max L.) and wheat (Triticum aestivum L.) seedlings to cadmium (Cd) stress and to investigate the alleviation effects of Ca and K on rhizotoxicity and absorption of Cd by roots. Soybean and wheat seedlings in a hydroponic system were exposed to Cd‐spiked solutions (0, 4, 8, 12, and 16 μM) with different Ca (0.5, 1, and 10 mM) and K (0.3, 1.2, and 9.6 mM) levels for 7 d. The results showed a dramatic reduction in root elongation of soybean due to increased Cd, but increasing Ca and K levels alleviated this reduction in soybean. The amelioration of Cd toxicity by the addition of Ca may be associated with reduced Cd absorption. However, the addition of K in reducing Cd toxicity might not be dependent upon Cd absorption. Compared with soybean, wheat showed a relatively high tolerance to Cd. The alleviation of Cd rhizotoxicity in wheat was more apparent by K than by Ca. We found that the addition of K promoted root elongation but not directly prevent Cd stress, and that the addition of Ca minimized acute rhizotoxicity of Cd in wheat. Moreover, the addition of Ca reduced Cd absorption by soybean and wheat roots. However, the addition of K only reduced Cd absorption by wheat roots.     

Response of Two Olive Cultivars to Salt Stress and Potassium Supplement

ABSTRACT

The effects of saline water containing 0, 50, 100, and 150 mM sodium chloride (NaCl), and 100 mM NaCl + 100 mM potassium (K) on photosynthesis, water relations, and ion and carbohydrate content of olive (Olea europaea L.) cultivars ‘Koroneiki’ and ‘Mastoidis’ were studied on five-year-old trees. Salinity increased sodium (Na⁺) and chloride (Cl^?) in tissues of both cultivars, but more so in ‘Koroneiki’ than in ‘Mastoidis.’ Salt-toxicity symptoms were observed at 100 and 150 mM, but not in plants receiving extra K. In salt-stressed plants, leaf water potential declined, whereas turgor potential remained positive due to a rapid decrease in osmotic potential. Salinity increased mannitol content up to 41.3% in ‘Mastoidis’ and 15.8% in ‘Koroneiki’, but reduced starch content in leaves. Photosynthetic rates fell significantly with increasing salinity in both cultivars, but more so in ‘Koroneiki’ than in ‘Mastoidis’. Potassium supplements reduced the concentration of Na⁺ and increased the concentrations of K⁺ in leaves, but decreased photosynthesis.     

Salinity and Defoliation Effects on Soybean Growth

An experiment was conducted to determine if salinity stress alters the response and tolerance of soybean to defoliation. Four soybean [Glycine max(L.) Merr.] cultivars (‘Tachiutaka,’ ‘Tousan 69,’ ‘Dare’ and ‘Enrei’) in a growth chamber were exposed to two salinity treatments (0 and 40 mM NaCl) and two defoliation treatments (with and without defoliation). The interactive effects of salinity stress and defoliation on growth rate, leaf expansion, photosynthetic gas exchange, and sodium (Na⁺) accumulation were determined. The decrease in growth rate resulting from defoliation was more pronounced in plants grown under salinity stress than in those grown without the stress. Without salinity stress, defoliated plants of all four cultivars had leaf-expansion similar rates to those of the undefoliated ones, but the photosynthetic rates of their remaining leaves were higher than those of undefoliated plants. However, with salinity stress, defoliated ‘Tachiutaka’ and ‘Tousa 69’ had lower leaf expansion and photosynthetic rates than undefoliated plants. For cultivars ‘Dare’ and ‘Enrei,’ the defoliated plants had leaf-expansion rates similar to undefoliated ones, but the photosynthetic rate of the remaining leaves did not increase. Except for cultivar ‘Dare,’ defoliated plants grown under salinity stress had higher Na⁺ accumulation in leaves than undefoliated ones, and this result may be related to slow leaf expansion and photosynthesis. Salinity stress negatively affects soybean response and tolerance of defoliation, and the effects varied according to the salt tolerance of the cultivar.     

SILICON MITIGATES ULTRAVIOLET-B RADIATION STRESS ON SOYBEAN BY ENHANCING CHLOROPHYLL AND PHOTOSYNTHESIS AND REDUCING TRANSPIRATION

The aim of this study was to investigate the potential of silicon (Si) for alleviating Ultraviolet-B (UV-B) radiation stress based on changes in biomass, physiological attributes and photosynthetic characteristics of two soybean (Glycine max L.) cultivars, Kenjiandou 43 (‘K 43’) and Zhonghuang 35 (‘ZH 35’). The cultivars were raised with and without Si in the greenhouse, and then subjected to ambient, ambient + 2.7 kJ m^?2d^?1and ambient + 5.4 kJ m^?2d^?1of UV-B radiation. Depending on cultivar, plants suffered severe growth limitations under UV-B radiation, but the application of Si alleviated the adverse effects on growth and development by increasing the stem length, net photosynthetic rate (P_N) and leaf chlorophyll content. Concurrently, it decreased the stomatal conductance (Sc) and intercellular carbon dioxide (CO₂) concentration (Ci). In response to the UV-B radiation stress, the antioxidant enzyme activities of superoxide dismutase (SOD) increased by 41.2–72.7%, peroxidases (POD) by 49.5–85.7%, malodialdehyde (MDA) by 6.7–20.4% and soluble protein by 4.2–7.6%. The overall results indicated that media treatment with Si might improve soybean growth under elevated UV-B radiation through positive changes in biomass and some physiological attributes that were dependent on cultivar.     

Interaction Between Phosphorus Nutrition and Drought on Grain Yield,and Assimilation of Phosphorus and Nitrogen in Two Soybean Cultivars Differing in Protein Concentration in Grains

ABSTRACT

Drought affects many physiological and biochemical processes and thus reduces plant growth. Phosphorus (P) fertilization improves tolerance to drought stress in many plants. A greenhouse experiment examined the interactive effects of P nutrition and drought stress on P accumulation and translocation, yield, and protein concentration in grains of two cultivars of soybean [Glycine max (L.) Merr.]. Plants of cultivars ‘Heisheng 101’ (high protein in grains) and ‘Dongnong 464’ (low protein) were grown in a P-deficient soil supplied with 0–30 mg P kg^?1 soil. Drought stress was imposed at the initial flowering (R1) or the podding (R4) stage. Drought stress limited P accumulation and reduced P translocation to the seed. The addition of P enhanced the concentration and accumulation of nitrogen (N) and P in shoots and seeds of both cultivars. Drought stress decreased shoot biomass, grain yield, and P accumulation; the decrease was greater in ‘Dongnong 46’ than ‘Heisheng 101,’ and even more so if drought stress was imposed at R4 than at R1. In contrast, drought stress increased the concentration of N in shoot and protein in grains. The addition of P alleviated the effect of drought stress on plant growth, P accumulation, and grain yield in both cultivars but to a greater extent in ‘Dongnong 46’. The results suggest that application of P fertilizers could mitigate drought stress at the reproductive stage, resulting in less yield penalty and improvement of grain quality of soybean grown in P-deficient soils.     

Effect of Cadmium and Iron on Rice (Oryza Sativa L.) Plant in Chelator-Buffered Nutrient Solution

ABSTRACT

To better understand the mechanisms responsible for differences in uptake and distribution of cadmium (Cd), nutrient-solution experiments were conducted with different varieties of rice (Oryza sativa), ‘Khitish’ and ‘CNRH3’. The plants were grown in a complete nutrient solution with different levels of pCd (-log free Cd⁺² activity) and pFe [-log free iron (Fe⁺²) activity]. The required concentrations of chelating agent and metals were determined using a computerized chemical equilibrium model such as Geochem-PC. Experimental treatments included a combination of four pCd activity levels (0, 7.9, 8.2, and 8.5) applied as Cd (NO₃)₂ 4H₂O, and two pFe activity levels (17.0 and 17.8) applied as FeCl₃. The application of both Cd and Fe in solution culture significantly affected plant growth, yield, and Cd accumulation in plant tissue. In general, yield of rice was decreased by an increase in amount of solution Cd; however, yield response varied among the cultivars. At the 7.9 pCd level, yields of rice cultivars ‘Khitish’ and ‘CNRH3’ were reduced to 69% and 65%, respectively, compared with control plants. Root Cd concentrations ranged from 2.6 mg kg^?1 (control plants) to 505.7 mg kg^?1 and were directly related to solution Cd concentrations. In rice plants, Cd toxicity symptoms resembled Fe chlorosis. Differential tolerance of varieties to phytotoxicity was not readily visible, but a significant interaction of substrate Cd and variety was obtained from dry-matter yields. Significant interactions indicated that response of tissue Cd concentration, plant Cd uptake, and translocation of Cd to the aerial parts were dependent on variety as well as substrate Cd. Uptake of Cd by roots was significantly higher than by shoots. Higher Cd uptake by rice plants decreased the uptake of other beneficial metals.

The effect of Cd and Fe on the rate of phytometallophore release was also studied in the nutrient solution. Among the rice genotypes, ‘Khitish’ was the most sensitive to Cd toxicity. In both genotypes, with the onset of visual Cd-toxicity symptoms, the release of phytometallophore (PM) was enhanced. Among the rice varieties, ‘Khitish’ had the highest rate of PM release. Treatments with the metal ions studied produced a decrease in chlorophyll and enzyme activity. A decrease in concentrations of chlorophyll pigments in the third leaf was observed due to the highest activity level of Cd (pCd 7.9). Activities of enzymes such as peroxidase (POD) and superoxide dismutase (SOD) are altered by toxic amounts of Cd. Changes in enzyme activities occurred at the lowest activity of Cd (pCd 8.5) in solution. Peroxidase activity increased in the third leaf. Results showed that in contrast with growth parameters, the measurements of enzyme activities may be included as early biomarkers in a plant bioassay to assess the phytotoxicity of Cd-contaminated solution on rice plants. Evidence that Cd uptake and translocation are genetically controlled warrants the selection of varieties that assimilate the least Cd and that translocate the least metal to the plant part to be used for human and animal consumption.     

EFFECT OF ARSENIC ON GERMINATION,PHOTOSYNTHESIS AND GROWTH PARAMETERS OF TWO WINTER WHEAT VARIETIES IN IRAN

□ Effects of different arsenic (As) concentration (0–30 mg L^?1) on seed germination, root tolerance index, relative shoot height, root and shoot biomass, photosynthetic pigments and arsenic accumulation in two wheat varieties were investigated. Low concentrations of arsenic (0–2.5 mg L^?1) stimulated germination percentage, shoot and root elongation, plant biomass as well as chlorophyll content as compared with control, however, these factors all decreased gradually at high concentrations of arsenic (5–30 mg L^?1). ‘Zarin’ variety had a significantly higher tolerance to arsenic than ‘Sardari.’ Arsenic accumulation by plants root and shoot increased with the increasing arsenic concentrations in medium, which ‘Zarin’ had a higher ability to absorb and translocate arsenic to the shoots. Root accumulated more arsenic than shoot. The similar trend of chlorophyll content and wheat growth under different arsenic concentration suggesting that arsenic toxicity affects the photosynthesis which ultimately results in the reduction of wheat growth and yield.     

EFFECT OF ZINC ON CADMIUM TOXICITY IN WINTER WHEAT

This nutrient solution experiment investigated the effects of zinc (Zn) and cadmium (Cd) on winter wheat growth and enzymatic activity. Twelve nutrient solution treatments were prepared of four zinc levels (0, 0.5, 5 and 50 mg L^?1) and three cadmium levels (0, 5 and 50 mg L^?1). Cadmium concentrations ≥5 mg L^?1 decreased plant growth, superoxide dismutase activity, and leaf and stem zinc concentrations, but increased plant cadmium concentrations, proline content, and peroxidase and catalase activities. Root activity and zinc concentration were highest in the 5 mg L^?1 treatment and lowest in the 50 mg L^?1 treatment. Zinc concentrations ≥5 mg L^?1 inhibited plant growth, but increased proline content and cadmium concentration in stems and leaves. Low levels of zinc (0.5 mg L^?1) increased cadmium-induced toxicity in wheat plants but high levels of zinc (50 mg L^?1) reduced. In conclusion, these results indicated that the addition of zinc alleviated cadmium toxicity if the zinc/cadmium ratio was >10/1. Additional study needs to be done to quantify zinc content before zinc is supplied to alleviate cadmium toxicity.     

CHARACTERIZATION OF THE PHYSIOLOGICAL RESPONSE OF THE HIGHLY-TOLERANT TOMATO CV. ‘PONCHO NEGRO’ TO SALINITY AND EXCESS BORON

The variety of tomato (Solanum lycopersicum) called ‘Poncho Negro’ by farmers represents an important source of genetic resources of agricultural interest, because it has managed to thrive at levels of salinity and excess B that other varieties of the same species find impossible. This work was conducted under controlled growth conditions in a greenhouse, evaluating and obtaining plant material that served for physiological, chemical, and biochemical determinations. Stress conditions were supplied by irrigation, using different concentrations of sodium chloride (NaCl; 75 and 150 mM) and excess boron (B; 5 and 20 mg L^?1). The rate of net carbon dioxide (CO₂) assimilation, the quantum efficiency of photosynthesis and the relative water content (RWC) were measured. In addition, B, sodium (Na⁺), potassium (K⁺), and calcium (Ca²⁺), soluble sugars, and proline were quantified. The results suggest that ‘Poncho Negro’ accumulated Na⁺ mainly in the roots, partly limiting its entry into the aerial parts. In addition, it should be noted that the interaction of B and salinity reduced the movement of Na⁺ to the leaves. The ability of cv. ‘Poncho Negro’ to minimize leaf Na⁺ accumulation, accumulate more leaf B than control plants, and maintain its K⁺ level, when grown with an excess of B, possibly allowed the observed increase in the rate of photosynthesis. In addition, these tomato plants used proline and soluble sugars as osmo-regulators under high-B and saline conditions. Under all stress conditions studied, this variety of tomato was able to regulate its water content, with RWC values of approximately 86%.     

铝对大豆叶片水势和生理特性的影响

以2个大豆{Glycine max(L.)Merrill}品种华春18,浙春3号为材料,设置不同的铝浓度进行土培试验,研究铝对大豆叶片水势和一些生理特性的影响。结果表明:高浓度的铝对大豆生长明显不利。随铝浓度的增加,大豆叶片水势略有下降;蛋白质含量在三叶期有所上升,然后在五叶期开始下降;叶绿素含量除三叶期外都有明显下降;二个大豆品种的SOD活性变化明显不相同。从种间差异性来看,浙春3号抗铝胁迫的能力大于华春18。     

Photosynthetic Response of Maize Plants Against Cadmium and Paraquat Impact

The effects of cadmium (Cd) and/or paraquat (PQ) toxicity on photosynthesis in maize leaves were examined by measurement of gas exchange and chlorophyll content in hydroponically cultured plants. It was found that growth rate was distinctly influenced only by 100 µM Cd treatment. Chlorophyll a and chlorophyll b decreased along with the increase of Cd concentration, while PQ spraying, alone and combined with Cd, increased chlorophyll a content on the third and seventh experimental days. Generally, carotenoid content increased in response to Cd and PQ and reached the highest levels at 100 µM Cd. Rate of photosynthesis in maize decreased after Cd treatment. CO₂ assimilation was approximately 60% reduced at 50 µM Cd and 70% reduced in the presence of 100 µM Cd. PQ toxicity was partly overcome after the third day of exposure. Transpiration and stomatal conductance in maize leaves decreased on the third day along with Cd concentration and PQ spraying, except for the 25-µM Cd-treated plants. On the tenth day, the 25-µM Cd-treated plants and those from PQ-treated variants showed an increase of transpiration and stomatal conductance. Maize exhibited an ability to accumulate Cd in high quantities, especially in the roots—over 4,500 mg Cd/kg dry weight.     

Genotypic differences in effects of cadmium on growth and nutrient compositions in wheat

Abstract

A solution culture study was conducted to determine the genotypic difference in the effects of cadmium (Cd) addition on growth and on the uptake and distribution of Cd and other 11 nutrients in wheat plants. Cadmium addition at a rate of 1 mg L^?1 significantly reduced root and shoot dry matter production, shoot height, root length, chlorophyll content, and tillers per plant. On the average of 16 wheat genotypes used in study, Cd concentrations of Cd‐treated plants were 48.1 and 459 μg g^?1 dry weight (DW) in shoots and roots, respectively, and retained 77.91% of total Cd taken up in the roots. On the whole, Cd addition reduced the concentration of sulfur (S), phosphorus (P), magnesium (Mg), molybdenum (Mo), manganese (Mn), and boron (B), and increased iron (Fe), irrespective of the plant parts. The effect of Cd on the concentration of potassium (K), calcium (Ca), and copper (Cu) differed in shoots and roots. The significant difference existed among 16 wheat genotypes in their response to Cd in terms of growth and nutrient concentrations. Genotype E81513, which showed relatively less inhibition in growth, had the lowest shoot Cd concentration and more Cd accumulation in roots, while Ailuyuang had the highest Cd concentration and accumulation in shoot with lower Cd concentration in root. The significant interaction was found between Cd treatment and genotype for all nutrient concentrations in both shoot and root, except S and Zn in root.     

Exogenously Applied Citric Acid Enhances Antioxidant Defense and Phytoextraction of Cadmium by Willows (<Emphasis Type="Italic">Salix</Emphasis> Spp.)

The effect of exogenously applied citric acid (CA) on phytoextraction and antioxidant defense was analyzed using willow species (Salix viminalis, S. alba, and S. matsudana) grown in soil contaminated with cadmium (Cd). Citric acid has been used as a chelating agent for the purpose of accelerating the solubility of Cd in soil and enhancing the phytoextraction of selected plants. Willows were exposed to 6 mg/kg of Cd, following the same with citric acid (20 mM/kg soil). Results revealed a positive effect of citric acid in mobilization of accumulated Cd from roots to shoots and leaves. The addition of citric acid alleviated Cd toxicity by helping plants to overcome oxidative stress, through CA’s chelating properties and the increased activity of antioxidant enzymes. Different protection strategies were evident through modification of activities of antioxidant enzymes such as catalase (CAT), ascorbate-peroxidase (APx), and guaiacol peroxidase (GPx) in young versus mature leaves in plants exposed to Cd. Furthermore, results revealed that addition of citric acid may be beneficial in the reduction of the negative effect of Cd stress on photosynthesis. The efficiency of coupling phytoextraction with the chelating agents represents a good strategy for decreasing damages caused by cadmium and has good potential in decontamination of a polluted environment.     

Amelioration of Cadmium Contaminated Soils Using Cation Exchangers

ABSTRACT

The contamination of soil and water with cadmium (Cd) is an environmental issue worldwide. Using lettuce (Lactuca sativa cv. ‘Cos’) in a glasshouse-based growth trial, two cation exchange materials [a zeolite and a kaolin amorphous derivate (KAD)] were examined for their ability to remove Cd from the soil solution and hence decrease the uptake of Cd by plants. Zeolite (applied at a rate of 2.5 t ha^{? 1}) was ineffective at reducing Cd uptake and accumulation in lettuce. When applied at a rate of 2.5 t ha^{? 1}, the KAD significantly reduced Cd uptake in all soils examined (ranging from a 26 to 64% reduction). Thus, KAD is considered to be potentially beneficial for the growth of plants in Cd-contaminated soils, although care must be taken to ensure that growth is not limited by deficiencies of the other nutrients for which KAD has a high affinity.     

Effects of excess soil manganese on stomatal function in two soybean cultivars

Manganese tolerant ‘Lee’ and Mn sensitive ‘Forrest’ soybean cultivars were grown in a potting soil with no known Mn toxicity and in Loring soil treated with excess Mn. Manganese toxicity in Loring soil was induced by the addition of Mn at 0, 100, 200 and 400 ug g^‐1 as MnSO₄.H₂O. A preliminary experiment was conducted to determine the appropriate Mn stress levels for Lee and Forrest soybean cultivars in Loring soil. Because the Loring soil produced severe Mn toxicity in both cultivars, even with an intial pH of 4.9 and no added Mn, CaCO₃ (2 g kg^‐1 ) was added to Increase the pH to 6–6.3. Soil was analysed for extractable and water soluble Mn and plants for Mn, Ca and Fe.

A second experiment was conducted to determine the effect of Mn toxicity on stomatal function. The procedure was the same as in the first experiment except that the CaCO₃ treatment was 2.5 g kg^‐1 to raise soil pH to 6.2 ‐6.5. Plants were grown in a greenhouse for 10 days and then moved to a growth chamber before making stomatal conductance measurements. A steady state porometer (LI 1600) was used. Results indicated that Mn toxicity closed stomates and decreased transpiration rates. This effect was more pronounced in Mn sensitive Forrest than in Mn tolerant Lee.     

Responses of Wheat Genotypes to Zinc Fertilization Under Saline Soil Conditions

ABSTRACT

A greenhouse experiment with four bread wheat [Triticum aestivum L.] genotypes, ‘Rushan,’ ‘Kavir,’ ‘Cross,’ and ‘Falat,’ and a durum wheat [Triticum durum L.] genotype, ‘Dur-3,’ at two zinc (Zn) rates (0 and 15 mg Zn kg^?1 dry soil) and four salinity levels (0, 60, 120, and 180 mM NaCl) was conducted. After 45 d of growth, the shoots were harvested, and Zn, iron (Fe), potassium (K), sodium (Na), and cadmium (Cd) concentrations were determined. In the absence of added Zn, visual Zn deficiency symptoms were observed to be more severe in ‘Dur-3’ and ‘Kavir’ than in other genotypes. The effect of Zn deficiency on shoot dry matter was similar to its effect on visual deficiency symptoms, such that shoot growth was most depressed in ‘Kavir’ and ‘Dur-3.’ At the 180 mM treatment, Zn fertilization had no effect on shoot dry matter of genotypes. Genotypes with high Zn efficiency had greater shoot Zn content than genotypes with low Zn efficiency. In the absence of added Zn, the Dur-3, and ‘Cross’ genotypes had the highest and lowest Cd concentrations, respectively. Application of Zn had a positive effect on salt tolerance of plants.     

不同芹菜品种镉吸收和运转差异研究

【目的】 研究镉胁迫下芹菜生长、镉吸收和向上运转品种间差异,为筛选镉低积累型芹菜品种减少镉对人体的危害提供依据。 【方法】 以10个芹菜品种为试材进行基质无土栽培试验,基质为蛭石,营养液采用1/2华南农业大学叶菜类营养液配方,以只浇灌营养液的处理作为对照,浇灌含15 mg/L氯化镉（CdCl₂）的营养液为Cd胁迫处理;每3 d浇灌一次,每次浇灌0.2 L,累计浇灌15次,每盆Cd施用量为45 mg。移栽45 d后,测定生长指标与根、叶柄和叶片Cd含量。计算相对生长量（relative growth yield,RGY）和转运系数（translocation factor,TF）,并筛选出高、低Cd积累品种。分别对高、低Cd积累品种进行穴盘基育苗,14 d后采用华南农业大学叶菜类营养液配方进行营养液栽培,21 d后利用非损伤微测技术（non-invasive micro-test technology,NMT）测定根系分生区、伸长区和根毛区Cd2+离子流速。 【结果】 与非Cd胁迫相比,Cd胁迫使‘速生四季西芹王’、文图拉西芹’、‘四季小香芹’、‘实心香芹’、 ‘雪白芹菜’ 地下部受到显著抑制,对地上部无显著影响;Cd胁迫促进了 ‘四季小香芹’ 地上部生长;而 ‘种都金黄芹菜’、‘红芹’、‘鲍芹’ 地上部受到显著抑制,对地下部则无显著影响;‘马家沟芹菜’ 和 ‘速生香芹’ 地上部和地下部均生长均受到抑制。食用器官叶柄中Cd含量以 ‘种都金黄芹菜’ 和 ‘雪白芹菜’ 最高;‘速生香芹’ 和 ‘实心香芹’ 最低。地上部Cd含量高的 ‘种都金黄芹菜’ 和 ‘雪白芹菜’ 对Cd转运能力也最高;Cd含量低的 ‘速生香芹’ 对Cd转运能力也最低。在根系成熟区（根毛区）,‘种都金黄芹菜’ 较 ‘速生香芹’ 有更高Cd2+ 离子流速。 【结论】 Cd胁迫下,芹菜不同品种生长、Cd吸收、转运和积累存在显著差异。‘四季小香芹’、‘速生四季西芹王’、‘文图拉芹菜’、‘实心香芹’ 和 ‘雪白芹菜’ 较为耐镉;而 ‘种都金黄芹菜’、‘红芹’、‘鲍芹’、‘马家沟芹菜’ 和 ‘速生香芹’ 对镉敏感。‘雪白芹菜’ 和 ‘种都金黄芹菜’ 为高Cd积累型,‘实心香芹’ 和 ‘速生香芹’ 为低Cd积累型,其中 ‘实心香芹’ 表现为低Cd含量和高生长量。高Cd积累型芹菜较低Cd积累型芹菜有更强Cd2+ 吸收能力和Cd转运能力,根部Cd2+ 流速可用于低积累品种的快速筛选。      

Effects of Exogenous Nitric Oxide and 24-Epibrassinolide on the Physiological Characteristics of Peanut Seedlings Under Cadmium Stress

Cadmium(Cd) is highly toxic to plants, animals, and humans. Limited information is available on the role of nitric oxide(NO)and/or 24-epibrassinolide(EBR) in response of plants to Cd stress. In this study, a hydroponic experiment was performed to investigate the effects of NO and/or EBR on peanut plants subjected to Cd stress(200 μmol L~(-1)) with sodium nitroprusside(SNP, an exogenous NO donor)(250 μmol L~(-1)) and/or EBR(0.1 μmol L~(-1)) addition. The results showed that Cd exposure inhibited plant growth, and this stress was alleviated by exogenous NO or EBR, and especially the combination of the two. Treatment with Cd inhibited the growth of peanut seedlings, decreased chlorophyll content, and significantly increased the Cd concentration in plants. Furthermore, the concentration of reactive oxygen species(ROS) markedly increased in peanut seedlings under Cd stress, resulting in the accumulation of malondialdehyde(MDA) and proline in leaves and roots. Under Cd stress, applications of SNP, EBR, and especially the two in combination significantly reduced the translocation of Cd from roots to leaves, increased the chlorophyll content, decreased the concentrations of ROS, MDA, and proline, and significantly enhanced the activities of superoxide dismutase(SOD), peroxidase(POD), and catalase(CAT) in peanut seedlings. Exogenous NO and/or EBR also stimulated the activities of nitrate reductase(NR)and nitric oxide synthase(NOS) and increased the contents of antioxidants, such as ascorbic acid(AsA) and reduced glutathione(GSH). Furthermore, exogenous NO and/or EBR enhanced Cd accumulation in the cell wall and thus decreased Cd distribution in the organelles in the roots. The concentrations of calcium(Ca), iron(Fe), magnesium(Mg), and zinc(Zn) were also regulated by exogenous NO or EBR, and especially by the two in combination. These results indicated that SNP and EBR, alone and particularly in combination, can mitigate the negative effects of Cd stress in peanut plants.     

Potassium Substitution by Sodium in Root Medium Influencing Growth Behavior and Potassium Efficiency in Cotton Genotypes

ABSTRACT

Potassium (K) deficiency affects cotton (Gossypium hirsutum L.) growth. Sodium (Na) can substitute K for some non-specific functions in plants. Four cotton genotypes were evaluated for their growth rates and K use efficiency grown at various K:Na. The cotton genotypes and treatments had significant (p < 0.01) effect on biomass production, growth rate related parameters, K use efficiency, and K: Na ratio. Maximum total dry matter (2.57 g plant^-1) was accumulated by ‘NIBGE-2’ and minimum (1.91 g plant^?1) was by ‘FH-1000’. Maximum K:Na ratio in shoot was obtained by ‘MNH-786’ and minimum was by ‘NIBGE-2’when 1/3rd K was replaced with Na. Genotypes and various treatments significantly (p < 0.05) influenced specific utilization rate (SUR) and K transport rate (KTR). There was a significant relationship (R² = 0.84, n = 60) between shoot dry matter and K: Na ratio in shoot. Overall, the growth was better when K and Na were added in ratio of 3:1.