Nitrogen Metabolism in Tomato Plants Under Cadmium Stress

Abstract

Young seedlings of tomato (Lycopersicon esculentum Mill.) grown on nitric medium and treated with different cadmium (Cd) concentrations (0–50 µM) were used. Results obtained show that Cd remains predominantly located in the roots, which then seem to play the role of trap‐organs. Increasing Cd concentration in the medium leads particularly to a decrease in NO₃ ^? accumulation, together with decrease in the activities of nitrate reductase (NR), nitrite reductase (NiR), and glutamine synthetase (GS). On the other hand, stimulations were observed for ammonium accumulation, anabolitic activity of glutamate dehydrogenase (GDH) and protease activity. Contrarily, decreases were obtained for soluble protein contents and catabolitic activity of GDH. These results were discussed in relation to the hypothesis attributing to the mitochondrial enzyme NADH‐dependent GDH, an important role in the plant defense processes, in maintaining the glutamate pool in conditions where the need for NH₄ ⁺ detoxification is increased by heavy metals.     

Oxidative Stress Induced by Cadmium and Copper in Brassica rapa Leaves: Indicators of Stress,Oxidative Damage,and Antioxidant Mechanisms

Brassica rapa is frequently used as a vegetable for human consumption and can accumulate metals that are bioavailable in soils. We studied the oxidative stress induced by 25 μM cadmium (Cd) and 50 μM copper (Cu) on Brassica rapa leaves and evaluated the intracellular antioxidative plant response mechanisms and the accumulation of these metals. With this purpose, hydrogen peroxide (H₂O₂) concentration, lipid peroxidation, and enzymatic and nonenzymatic responses was determined. The obtained results indicate that Cd and Cu induced different plant responses. Oxidative stress induced by Cu was characterized by increased lipid peroxidation and free proline levels. Guaiacol peroxidase and ascorbate peroxidase showed a relevant role in H₂O₂ removal. Cadmium did not influence lipid peroxidation, H₂O₂, proline and glutathione contents, and the enzymatic response mainly involves superoxide dismutase and ascorbate peroxidase. It was concluded that both excess Cu and Cd induced oxidative stress but plant response is characterized by different antioxidative response mechanisms.     

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.     

Effect of Zinc on Cadmium Toxicity-Induced Oxidative Stress in Winter Wheat Seedlings

Two hydroponic experiments were conducted to investigate the antioxidant response of winter wheat (Triticum aestivum L.) to cadmium (Cd)-zinc (Zn) interactions, Seedlings of winter wheat (cv. Yuandong 977), were grown in modified Hoagland nutrient solution with the addition of increasing concentrations of Cd (0, 10, 25, 50 μM). In experiment 2, the seedlings of the same cultivar were treated with constant concentration of Cd (25 μM) and varying levels of Zn (0, 1, 10, 50 μM). Hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) as well as the activities of three antioxidant enzymes, catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) were monitored to estimate the amount of oxidative stress and the antioxidant ability of seedlings treated with Cd and Zn for 10 days. The results showed that levels of H₂O₂ and MDA in experiment 1 were significantly increased with increasing Cd concentrations. The data indicated that Cd could induce oxidative stress and lipid peroxidation in the plants. While H₂O₂ and MDA levels were significantly reduced by addition of Zn in experiment 2, the activities antioxidant enzymes were enhanced. A concentration of 10 μM Zn appeared to be the optimal level in this experiment for seedlings' growth, chlorophyll synthesis and antioxidant status, indicating that Zn alleviated the oxidative stress induced by Cd.     

Involvement of Excess Cadmium on Oxidative Stress and Other Physiological Parameters of Eggplant

To examine tolerance of cadmium (Cd) by eggplant (Solanum melongena L.) cv. ‘Hybrid PK 123’, plants were grown in refined sand in complete nutrient solution for 52 days in a glasshouse at ambient temperature. Cadmium sulfate was superimposed on day 53, at variable levels: nil, 0.05, 0.1, 0.2, 0.4, and 0.5 mM. Influence of excess Cd was discernible after 5 days of metal supply at 0.4 and 0.5 mM Cd as depression in growth. At these levels, foliar symptoms were initiated as paling of young leaves at the base progressing upward. With increase in age, affected leaves turned golden yellow and these effects spread to lower leaves. Leaf size and floral initiation were very much restricted. These types of phenotypes induced leaf senescence. Excess Cd reduced the biomass and fruit yield of plants. At higher levels (>0.1 mM) of Cd, fruit formation was completely inhibited and fruits formed at 0.05 and 0.1 mM Cd were smaller in size. Besides this, excess Cd disturbed the metabolism of eggplant by reducing the concentration of chlorophyll (a and b), protein, Hill reaction activity, and activity of antioxidant enzymes—catalase and ascorbate peroxidase; whereas the activity of peroxidase and ribonuclease increased in leaves of eggplant. Cadmium excess reduced the concentration of Fe and Zn and Cd increased that of proline, lipid peroxidation, phenols, reducing sugars and Cd concentration in leaves of eggplant.     

Cadmium Effects in Sunflower: Nutritional Imbalances in Plants and Calluses

The effects of cadmium (Cd) exposure on sunflower (Helianthus annuus L.) nutrient accumulation remain unclear. However, studies concerning crop improvement for Cd tolerance suggest the use of biotechnology techniques such as tissue culture. It is still unknown whether in vitro cells respond to Cd exposure in a way similar to plants. In this paper, the objectives were (1) to characterize the effects of Cd exposure in macronutrient and micronutrient accumulation in different sunflower organs/tissues and (2) to compare the behavior of two culture systems (plants vs. tissue culture) regarding Cd and nutrient accumulation. To achieve these aims, sunflower plants were grown hydroponically in the presence of Cd (at levels of 0, 5, 50, and 500 μ M). For in vitro cultures, seeds were germinated axenically and leaf explants were then grown on Murashige and Skoog medium (MS). One-month-old calluses were grown on MS medium containing 0, 5, 50, and 500 μ M Cd. After 21 d of exposure to 500 μ M, all plants were dead. The contents of macro- and micronutrients and of Cd were determined by ICPS in 18 d-exposed plants and calluses and in calluses exposed for six months to 50 μ M Cd. At day 18, Cd content increased in leaves, roots, and calluses. Cadmium exposure also decreased the contents of magnesium (Mg), calcium (Ca), iron (Fe), and manganese (Mn) in roots and of Mg, Ca, copper (Cu), Fe, and Mn in shoots. Exposed calluses suffered decreases only in Mg, Ca, and Mn contents. The contents of most of these nutrients in six-month-exposed calluses were similar to those of the control calluses, indicating that these long-term exposed in vitro cells developed mechanisms for regulating the effects of Cd on the accumulation of nutrients.     

Protective Role of Putrescine Against Salt Stress is Partially Related to the Improvement of Water Relation and Nutritional Imbalance in Cucumber

Polyamines play a variety of physiological roles in plant growth and development. To investigate whether exogenous putrescine (Put) has roles in protecting plants against salt stress, Put (100 μ M) was added to nutrient solution three days before cucumber (Cucumis sativusL. cv. “Jinyan No.4') seedlings were exposed to 100 mM sodium chloride (NaCl) treatment. Putrescine treatment significantly ameliorated the detrimental effects of NaCl on root growth and this was associated with a decrease of Na uptake and an increase in potassium accumulation in roots. Manganese (Mn) content in roots was decreased by salinity stress but increased by Put pretreatment. Furthermore, osmotic stress associated with NaCl treatment decreased leaf water potential and water content, while these effects were alleviated by Put pretreatment. The decreases in net photosynthetic rate (Pn) and stomatal conductance (Gs) by NaCl were also diminished by Put treatment. The results indicate that Put may play an important role in protecting cucumber plants against salt stress.     

镉胁迫下磷酸二铵对小麦生长及吸收镉的影响

以黄土和小麦为供试对象,通过盆栽试验研究了不同Cd胁迫水平下施用(NH4)2HPO4对小麦生长及Cd富集、转移的影响。结果表明,Cd胁迫对小麦的生长表现为低促高抑,Cd胁迫下施用(NH4)2HPO4可促进小麦的生长,尤其是茎叶的生长;小麦各部位的Cd含量均随着土壤Cd胁迫水平的升高而升高,且根系茎叶籽粒。施用(NH4)2HPO4能促进小麦对Cd的吸收,对根系和籽粒的促进作用大于茎叶;小麦各部位对Cd的富集能力均随着土壤Cd胁迫水平的升高而先增加后减小,而茎叶的转移能力先降低后升高,籽粒反之。施用(NH4)2HPO4显著促进根系对Cd的富集和茎叶对Cd的转移。     

圆叶决明（Chamaecrista rotundifolia）对重金属镉胁迫的响应及镉吸收效果研究

以圆叶决明2228（Chamaecrista rotundifolia）为材料,采用土培法,研究重金属镉对圆叶决明2228保护酶（SOD和POD）、生长（生物量、株高、SPAD值和含水量等）的影响,同时分析圆叶决明对镉的吸收效果。结果表明,重金属镉胁迫下圆叶决明2228保护酶活性均随着镉处理浓度的升高呈先升后降的趋势,其中20mg·kg^-1镉胁迫下SOD酶活性最强,50mg·kg^-1镉胁迫下POD酶活性最强;镉对圆叶决明的生长抑制表现为抑制植物的生长,降低株高和生物量,但与叶绿素相关的SPAD值无显著变化。通过镉含量分析可知,圆叶决明2228吸收的镉量均未超过镉临界指标含量,因此该植物不是镉超富集植物,但生物富集系数大于1,为镉耐性植物。由于圆叶决明生长过程中生物量大,在生长过程中可通过生物量带走部分重金属镉,圆叶决明2228具有修复轻度镉污染土壤的潜能。     

蔬菜废弃物栽培基质对番茄生长发育和营养品质的影响

[目的]了解有机生态型蔬菜栽培基质对番茄生长发育及营养品质的影响,为蔬菜废弃物微生物发酵物在生产上的推广应用提供科学依据。[方法]采用自然条件下室外堆肥、基质研制及温室盆栽试验进行分析研究。[结果]有机生态型基质各配方处理对番茄的株高、展幅、主茎粗、结果数、产量均有明显的促进作用,C处理即配方为蔬菜废弃物∶玉米秸秆∶牛粪∶发酵菌剂,配比为100∶4∶2∶0.25的处理,其番茄的产量较对照增长了97%,该处理番茄的干物质、有机酸、可溶性糖、维生素C等营养品质指标,与对照相比分别增加了41.9%,139.6%,36.8%和18.7%,特别是该处理番茄的可溶性固形物含量比对照增加了57.1%。各配方处理番茄的亚硝酸盐、重金属等有害残留均低于对照,符合国家相关标准规定。[结论]有机生态型基质各配方处理对番茄的生长发育和营养品质均有一定的促进作用。     

生物炭对镉胁迫下花生根系形态学特性及根镉含量的影响

试验采用盆栽方式,在3种不同镉(Cd)污染土壤中分别施用4种用量生物炭(C),探讨生物炭对镉胁迫下花生根长、根直径、根体积、侧根数、根系生物量和根镉含量影响。研究结果表明,在花生同一生长时期,相同镉处理条件下,花生的各项根系指标随着生物炭施入量的加大而逐渐增加,且这种趋势随着生育时期的延长变得更明显。在C100、C150处理下,苗期花生的根直径、侧根数和根系生物量随着Cd浓度的增加呈现Cd1Cd10Cd0的趋势,表明生物炭的施入,增加了花生苗期的镉耐性;而花生结荚期,不同生物炭施入处理下,花生各形态学指标均呈现Cd0Cd1Cd10的趋势,显示出在花生生殖后期,前期低浓度镉产生的刺激作用逐渐消失,生物炭对镉胁迫的缓解作用与花生发育时期有关。花生根镉含量与生物炭施用量之间存在极显著负相关关系,相关系数范围在-0.988至-0.922之间。灰色关联度分析显示,在花生苗期和花针期,侧根数、根系生物量是影响根镉含量的主要因素。研究未发现过多的生物炭施入对作物根系形态学指标的抑制作用。     

两种基因型龙葵对镉胁迫的生理响应及镉吸收差异

采用盆栽试验,通过研究不同浓度镉（0、5、25、50、100μg·g-1）胁迫下红果龙葵和少花龙葵幼苗根、茎和叶的生物量变化、镉吸收量、镉转移率、镉富集系数和叶片抗氧化酶（SOD、POD）活性、叶片可溶性蛋白和游离脯氨酸含量等指标的变化,比较2种基因型龙葵富集镉的差异。结果表明,2种基因型龙葵富集重金属镉存在明显差异。与对照相比,在Cd胁迫浓度≥25μg·g-1时,2种龙葵的生物量显著下降（P〈0.05）,而少花龙葵的下降趋势较红果龙葵小;随着Cd胁迫浓度的增加,2种龙葵根、茎和叶的Cd吸收量显著上升（P〈0.05）,且根部Cd含量高于茎和叶,而少花龙葵的根、茎和叶中的Cd含量均高于红果龙葵,2种龙葵的镉转移率和富集系数除5μg·g-1Cd胁迫外,均小于1,且少花龙葵对镉转移率和镉富集系数均大于红果龙葵。2种龙葵叶片可溶性蛋白、游离脯氨酸含量以及抗氧化酶（SOD、POD）活性均表现为先上升后下降,均表现为少花龙葵上升幅度大而下降幅度较小。综合各项指标表明,2种龙葵均不是Cd的超积累植物,少花龙葵的耐Cd胁迫能力较红果龙葵强。     

Factors and Predictions for Cadmium Transfer from Soils into Tomato Plants

Soil-plant transfer models are needed to predict levels of cadmium (Cd) in vegetables when evaluating the food chain risks of Cd contamination in agricultural soils. In the present study, the transfer of Cd from a wide range of soils into tomato plants was investigated in order to identify the major factors and to develop predictive models. It was found that soil pH was the main factor controlling Cd uptake and lower pH was more favorable for Cd bioaccumulation. Furthermore, the hydrogen ion activity, other than pH, was correlated linearly with the ratio of plant Cd to soil Cd. Combining soil Cd, and the interaction between soil Cd and hydrogen ion activity greatly improved the model to predict the transfer of Cd from soil to plant. Compared with the previous log transformation model, the predicted model improved the regression coefficient from 0.799 to 0.973 and has important significance in practice.     

Effects of Grafting on Alkali Stress in Tomato Plants: Datura Rootstock Improve Alkalinity Tolerance of Tomato Plants

Plant growth, nutritional status, and proline content were investigated in non-grafted and grafted greenhouse tomato plants onto five rootstocks of eggplant, datura, orange nightshade, local Iranian tobacco, and field tomato, exposed to 0, 5, and 10 mM sodium bicarbonate (NaHCO₃) to determine whether grafting could improve alkalinity tolerance of tomato. The leaf fresh mass of ungrafted and grafted tomato plants decreased significantly as NaHCO₃ levels increased. Despite other rootstocks and ungrafted plants, alkalinity had no significant effect on stem and root fresh mass and shoot phosphorus (P), potassium (K) and magnesium (Mg) concentrations of datura grafted plants. The lowest solution pH and electrical conductivity (EC) values and the highest leaf proline content were observed in the plants grafted onto datura rootstock. Moreover, sodium (Na) concentration in shoots was lower in plants grafted onto datura rootstock than in other plants especially under high NaHCO₃ levels. Overall, using datura rootstock improved alkalinity tolerance of tomato plants under NaHCO₃ stress.     

脱落酸对番茄部分果实性状和营养品质的影响

为研究脱落酸(ABA)对番茄果实品质的影响,本研究测定了番茄ABA生物合成缺失突变体not和flc及其野生型各成熟时期果实,以及外源100μmol·L^-1 ABA处理后不同天数的番茄果实的外观品质和营养品质。结果表明,内源ABA缺失抑制番茄果实增重并促进果实纵向生长,但对果实硬度无明显影响。同时,内源ABA可影响番茄果实可溶性固形物含量并促进破色期和转色期的还原糖积累。not和flc果实中番茄红素、β-胡萝卜素、叶黄素和总类胡萝卜素含量均显著高于其野生型,且外源喷施试验表明,与对照组相比,外源100μmol·L^-1 ABA处理能显著抑制番茄果实中番茄红素、β-胡萝卜素和总类胡萝卜素的积累。综上,ABA在调控番茄果实外观品质方面,可促进番茄果实增重并抑制番茄果实纵向生长;在调控番茄果实营养品质方面,可促进还原糖积累并抑制类胡萝卜素积累。本研究结果为利用ABA调控番茄果实品质提供了一定的理论依据和技术支持。     

镉胁迫对菊芋生理变化及镉富集的影响

通过用耐镉性较好的徐州菊芋和耐镉性较弱的潍坊菊芋进行对比试验,设置土培CK(Cd~(2+) 0 mmol/L,即对照组)、T1(Cd~(2+) 0.1 mmol/L)、T2(Cd~(2+) 0.5 mmol/L)和T3(Cd~(2+) 1.0 mmol/L)4个处理组,探讨菊芋镉胁迫下各项生理指标和根际土壤指标以及富集能力的影响。结果表明:经过不同镉浓度胁迫21天后,2个菊芋品种的根长、株高、叶长、叶宽均受到相应程度的抑制,抗氧化酶活性随镉浓度的增加而减弱;但丙二醛(MDA)含量变化有所不同,潍坊菊芋的MDA含量伴着镉胁迫加深而增加,徐州菊芋只在T3镉浓度下才出现明显的上升变化,并在21天时达到峰值,为对照组的3.52倍。根际土壤pH大致呈现出持续下降趋势,镉处理20天时潍坊菊芋和徐州菊芋根际土壤pH均在T3处理下达到最低,降幅分别为3.85%和3.41%;有机质含量却表现出不断增加的状态,T3镉处理至第20天时,潍坊菊芋最大增幅为38.60%,徐州菊芋为36.01%;随着施加镉浓度的变大,抑制了菊芋对土壤碱解氮的吸收,总体上潍坊菊芋受抑制程度大于徐州菊芋。2个菊芋品种对镉的富集效果也不同,徐州菊芋各器官镉富集量均高于潍坊菊芋;在转运镉方面,潍坊菊芋根部的镉均等地转移到了叶、茎上,徐州菊芋则将大部分从根部转移到茎上。综上所述,菊芋在镉胁迫下体现出一定的抗性,具有较强镉富集能力,徐州菊芋镉富集能力更为明显。因此,将能源植物菊芋应用于镉污染土壤兼具经济和生态意义。     

不同基因型番茄幼苗对镉胁迫的生理响应及镉吸收差异

采用盆栽试验,通过研究不同浓度镉（1、5、10mg·kg-1）胁迫下4种基因型番茄圣粉1号、东圣1号、农城906和宝冠1号幼苗地上部及根部生物量、镉吸收量、活性氧含量（ROS）及其他生理指标,筛选出镉低积累基因型番茄品种。结果表明,不同基因型番茄对镉胁迫响应存在差异。随镉处理浓度增加,4个品种番茄幼苗地上部生物量显著下降（P〈0.05）。地上部Cd吸收量呈增加趋势,在中浓度（5mg·kg-1）镉处理下达到峰值,品种间为宝冠1号〉圣粉1号、农城906〉东圣1号。4个品种番茄幼苗Cd转移率随镉处理浓度增加显著降低,其中东圣1号Cd转移率较低,根部Cd滞留较多,向地上部转移较少。4个品种番茄幼苗生理活性存在差异,宝冠1号番茄幼苗ROS含量及抗氧化酶（POD,CAT）活性随镉处理浓度增加变化幅度较大,东圣1号变化幅度相对较小。综合各项指标,4个基因型番茄中东圣1号为镉低积累品种。     

Molybdenum Stress Modulates Enzymes Responsive to Oxidative Stress and Affects Seeds Viability and Vigor in Chickpea

The importance of molybdenum (Mo) for plant growth is disproportionate with respect to the absolute amounts required by most plants. Chickpea (Cicer arietinum L.) cv. K-75 plants were raised in refined sand in glasshouse at graded levels from 0.002 to 1 µM for 100 days. Mo deficiency symptoms appeared as interveinal chlorosis of middle and old leaves. Compared with the control (0.2 µM Mo), dry matter, yield and seed protein decreased at low and excess Mo. The concentration of Mo in leaves and seed as well as the activity of nitrate reductase (NR) increased with an increase in Mo supply. The activities of antioxidative enzymes stimulate at both low and excess Mo supply. Low and excess Mo decreased the lipid peroxidation status in chickpea leaves, suggesting its antiperoxidative nature. The values of deficiency, threshold of deficiency and threshold of toxicity of Mo were, respectively, 0.38, 1.2 and 15 µg g^?1 in leaves of chickpea.     

镉胁迫对白车轴草生长、镉含量及养分分配的影响

为了解镉(Cd)胁迫对白车轴草(Tritolium repens L.)生长发育以及养分的吸收、累积与分配的影响,采用盆栽试验,研究了不同浓度镉处理下白车轴草幼苗的生长、生物量及碳(C)、氮(N)、磷(P)和钾(K)的积累与分配特征。结果表明:随镉胁迫浓度增加,植株幼苗叶面积、主根长、侧根数、侧根长及地上部高先升高后降低,叶柄长明显降低;而根、茎、叶中镉含量逐渐升高,且根系大于茎叶。同时,植物各器官生物量生产及C、N、P和K积累量均表现出随镉添加量的增加而先升高后降低,高浓度镉胁迫处理(50.00、100.00和200.00 mg·kg-1)明显抑制植株生物量生产以及C、N、P和K的积累,显著改变了生物量及其C、N、P和K积累量的分配格局,但低浓度镉处理(12.50mg·kg-1)却无明显影响。一定浓度的镉胁迫处理(12.50和25.00 mg·kg-1)降低植株N、P、K的利用效率,但高浓度镉处理(200.00 mg·kg-1)则提高植株N、P、K的利用效率。本研究为城市园林绿化及镉污染土壤的修复提供了应用潜力,同时也为牧草的安全评估提供了科学借鉴。