Effects of Selenium on Wheat Seedlings Under Drought Stress

The paper reports the effects of selenium (Se) supply on growth and some physiological traits of wheat (Triticum aestivum L. cv Shijiazhuang NO. 8) seedlings exposed to drought stress. The growth and physiological responses of seedlings were different depending on the Se concentration. The higher (3.0 mg Se kg⁻¹) and lower amount used (0.5 mg Se kg⁻¹) did not significantly affect on biomass accumulation. Treatments with 1.0 and 2.0 mg Se kg⁻¹ promoted biomass accumulation of wheat seedlings. Treatments at 1.0, 2.0, and 3.0 mg Se kg⁻¹ significantly increased root activity, proline content, peroxidase (POD), and catalase (CAT) activities, carotenoids (Car) content, chlorophyll content, and reduced malondialdehyde (MDA) content of wheat seedlings. Lower Se treatment did not significantly effect on chlorophyll content and MDA content, although it also increased some antioxidant index (proline and Car content, POD and CAT activities) in wheat seedlings. These results suggest that optimal Se supply is favorable for growth of wheat seedlings during drought condition.     

Effects of drought stress and selenium supply on growth and physiological characteristics of wheat seedlings

The paper studied the effects of drought stress, selenium (Se) supply and their combination on growth and physiological characteristics of wheat (Triticum aestivum L. cv Shijiazhuang NO. 8) seedlings. The experimental design included two water treatments (well-watered, 75% of maximum field capacity; drought stress, 30% of maximum field capacity) and two Se levels (0; 0.5 mg/kg) to determine whether Se can modify the negative impacts of drought stress on seedling growth and physiological traits. Drought stress caused a marked decline in growth parameters and soluble protein content, whereas it induced an increase in root activity, proline content and the activities of peroxidase (POD) and catalase (CAT) of leaf tissue. On the other hand, Se supply induced an increase in biomass accumulation only under well-watered condition. Under drought stress, Se supply increased free proline content, root activity and the activities of POD and CAT in leaf tissue, but did not significantly affect on growth parameters. These results implied that drought stress brought harmful effects on wheat seedlings, and that Se supply was favorable for biomass accumulation of wheat seedlings under well-watered condition. However, it did not significantly affect on biomass accumulation under drought stress, although it increased root activity and activities of some antioxidant index in experimental periods.     

Exogenous nitric oxide promotes waterlogging tolerance as related to the activities of antioxidant enzymes in cucumber seedlings

We investigated the effects of exogenous sodium nitroprusside (SNP), a nitric oxide (NO) donor, on growth of cucumber (Cucumis sativus L., cv. Jinyou No.1) seedlings and antioxidant enzyme activities in cucumber leaves under waterlogging stress. The growth of cucumber seedlings was significantly inhibited when plants were exposed to waterlogging, whereas shoot spraying with SNP significantly alleviated the inhibition of growth from this type of stress: height, fresh and dry weights of the flooded plants increased obviously. Waterlogging also caused the activation of the antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX)), the reduction of the chlorophyll content, and the accumulation of MDA and protein in leaves. It was found that SNP treatment further potentiated the antioxidant enzyme activities and maintained the chlorophyll and protein content during the entire water-logging period; however, it reduced the MDA content. Thus, NO protects plants from oxidative damage and promotes growth by activation of antioxidant enzymes in leaves in an extent sufficient for the alleviation of membrane injury. However, exogenous NO had no significant effects on cucumber seedlings growth and antioxidant enzyme activities under nonstress conditions.     

Protective role of salicylic acid applied before cold stress on antioxidative system and protein patterns in barley apoplast

This study was carried out to better understand the role of salicylic acid (SA) applied before cold stress in the cold tolerance mechanism. Two barley (Hordeum vulgare) cultivars, cold-sensitive (Akhisar) and cold-tolerant (Tokak), were used and 0.1 mM SA was applied to 7-d-old barley seedlings growing under control conditions (20/18 °C). The seedlings were transferred to cold chamber (7/5 °C) at the age 14, 21, and 28 d. After three days, the leaves were harvested to determine the activities of apoplastic antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) and ice nucleation activity and electrophoretic patterns of apoplastic proteins. Cold treatment decreased the activities of all enzymes in cold-sensitive cultivar, however, it increased CAT and POX activities in cold-tolerant cultivar. Exogenous SA increased enzyme activities in both cultivars. Ice nucleation activity increased by cold treatment, especially in 17-d-old seedlings in both cultivars. In addition, SA treatment increased ice nucleation activity in all examined samplings in both cultivars. SA treatment caused accumulation or de novo synthesis of some apoplastic proteins. The results of the present study show that exogenous SA can improve cold tolerance by regulating the activities of apoplastic antioxidative enzymes, ice nucleation activity, and the patterns of apoplastic proteins.     

Exogenous Application of Selenium Mitigates Cadmium Toxicity in <Emphasis Type="Italic">Brassica juncea</Emphasis> L. (Czern &amp; Cross) by Up-Regulating Antioxidative System and Secondary Metabolites

The main aim of the present study was to examine the role of selenium (Se) in ameliorating the toxic effect of cadmium (Cd) in mustard (Brassica juncea) plants. The plants exposed to elevated levels of Cd exhibited reduced biomass, pigment content, and relative water content (RWC). However, supplementation of Se restores the negative effect of Cd and increases biomass, pigment content, and RWC. Osmolyte (proline and glycine betaine) and sugar content were increased under Cd stress and further increase was observed with addition of Se. Cd decreased protein content and supplementation of Se increases it to appreciable levels. Cd also increased production of H₂O₂ and lipid peroxidation, electrolyte leakage, and the activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and glutathione reductase. Supplementation of Se decreased accumulation of H₂O₂ and lipid peroxidation, increased the activities of antioxidant enzymes to greater levels, and regulates Cd accumulation in roots and shoots. Ascorbic acid (AsA) and flavonoids decreased with elevated concentrations of Cd; however, tocopherol and total phenols were increased with the same concentrations of Cd. Se application maintains AsA and flavonoid content, and further increase in tocopherol and total phenols were observed with Se in the present study. Overall the results confirm that exogenous application of Se mitigates the negative effects of Cd stress in mustard plants through the regulation of osmoprotectants, antioxidant enzymes, and secondary metabolites.     

Modulation of Antioxidant Machinery and the Methylglyoxal Detoxification System in Selenium-Supplemented Brassica napus Seedlings Confers Tolerance to High Temperature Stress

We investigated the protective role of selenium (Se) in minimizing high temperature-induced damages to rapeseed (Brassica napus L. cv. BINA Sarisha 3) seedlings. Ten-day-old seedlings which had been supplemented with Se (25 μM Na₂SeO₄) or not were grown separately under control temperature (25 °C) or high temperature (38 °C) for a period of 24 or 48 h in nutrient solution. Heat stress caused decrease in chlorophyll and leaf relative water content (RWC) and increased malondialdehyde (MDA), hydrogen peroxide (H₂O₂), proline (Pro), and methylglyoxal (MG) contents. Ascorbate (AsA) content decreased at any duration of heat treatment. The content of reduced glutathione (GSH) increased only at 24 h of stress, while glutathione disulfide (GSSG) markedly increased at both duration of heat exposure with associated decrease in GSH/GSSG ratio. Upon heat treatment the activities of ascorbate peroxidase (APX), glutathione S-transferase (GST) and glyoxalase I (Gly I) were increased, while the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and catalase (CAT) were decreased. The activities of glutathione reductase (GR) and glutathione peroxidase (GPX) remained unchanged under heat stress. However, heat-treated seedlings which were supplemented with Se significantly decreased the lipid peroxidation, H₂O₂, and MG content and enhanced the content of chlorophyll, Pro, RWC, AsA, and GSH as well as the GSH/GSSG ratio. Selenium supplemented heat-treated seedlings also showed enhanced activities of MDHAR, DHAR, GR, GPX, CAT, Gly I, and Gly II as compared to heat-treated seedlings without Se supplementation. This study concludes that exogenous Se application confers heat stress tolerance in rapeseed seedlings by upregulating the antioxidant defense mechanism and methylglyoxal detoxification system.     

Protective role of selenium in wheat seedlings subjected to enhanced UV-B radiation

Selenium (Se) is beneficial for some plants and is able to increase resistance and antioxidant capacity of plants subjected to stressful environment. In this work, the effects of enhanced ultraviolet-B (UV-B) radiation, Se supply, and their combination on growth and physiological traits of wheat (Triticum aestivum L., cv. Han NO.7086) seedlings were studied. The objective was to elucidate whether Se could alleviate the expected adverse effects of UV-B stress on seedlings. UV-B treatment caused a marked decline in growth parameters and total chlorophyll content and changed biomass allocation between aboveground and underground parts, which led to an increase in the root/shoot ratio. UV-B treatment also increased MDA content and the rate of superoxide radical (O₂^·−) production, although it increased some antioxidant (proline, phenolic compounds, and flavonoids) content and activity of antioxidant enzymes (peroxidase, superoxide dimutase, catalase (CAT)). Se treatment only increased total chlorophyll content and CAT activity. Compared with UV-B treatment alone, the combined treatment with UV-B and Se induced a significant increase in the biomass, total chlorophyll content, antioxidant content, and activity of antioxidant enzymes, and an evident decrease in MDA content and the rate of O₂^·− production. The results of this study demonstrated that Se alleviated the damage caused by UV-B to wheat seedlings to some extent by increasing antioxidant enzyme activity and antioxidant content.     

Antioxidant Responses of Wheat Seedlings to Exogenous Selenium Supply Under Enhanced Ultraviolet-B

The paper reports the effects of selenium (Se) supply on growth and antioxidant traits of wheat (Triticum aestivum L. cv Han NO.7086) seedlings exposed to enhanced ultraviolet-B (UV-B) stress. Antioxidant responses of seedlings were different depending on the Se concentration. Compared with the control, the lower amount used (0.5 mg Se kg⁻¹ soil) had no significant effect on biomass accumulation. The treatments with 1.0, 2.0, and 3.0 mg Se kg⁻¹ promoted biomass accumulation of wheat seedlings, and the increased amount in biomass was the most at 1.0 mg Se kg⁻¹ treatment. Se treatments with 1.0, 2.0, and 3.0 mg kg⁻¹ also significantly increased activities of peroxidase (POD) and superoxide dismutase (SOD) and reduced the rate of superoxide radical (O₂⁻) production and malondialdehyde (MDA) content of wheat seedlings. In addition, anthocyanins and phenolic compounds content in wheat seedlings evidently increased by the treatments with 1.0 and 2.0 mg Se kg⁻¹. The lower Se treatment had no significant effect on MDA content, although it increased activities of antioxidant enzymes (POD, SOD, and catalase activities) and reduced the rate of O₂⁻ production in wheat seedlings. These results suggest that optimal Se supply is favorable for the growth of wheat seedlings and that optimal Se supply can reduce oxidative stress of seedlings under enhanced UV-B radiation.     

24-Epibrassinolide ameliorates the effects of boron toxicity on <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> (L.) Heynh by activating an antioxidant system and decreasing boron accumulation

Brassinosteroids (BRs) play a significant role in alleviating the negative effects of various environmental stresses and in promoting the growth and development of plants. In this study, we investigated the effects of 24-epibrassinolide (EBL) on the growth, boron (B) accumulation and activation of the antioxidant system of Arabidopsis thaliana (L.) Heynh exposed to high concentrations of boric acid (BA). A. thaliana plants were grown in a hydroponic culture, and after 4 weeks, the plants were transferred to media containing either 0.80 or 1.60 mM BA. Following BA treatment, 0.01 and 1 µM EBL was sprayed on the entire foliar region of the seedlings. B toxicity induced oxidative stress and considerably inhibited the growth of the plants. The spraying of EBL on the B-treated plants resulted in increases in growth (both fresh and dry shoot mass, silique number, length and mass) and pigment content (total chlorophyll and carotenoids). Excessive B levels increased the activities of antioxidant enzymes, including superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase, and increased the proline content in leaves of plants. However, treatment of the B-stressed plants with EBL further enhanced the activities of the antioxidant enzymes and increased the content of proline. The high level of lipid peroxidation in plants observed during exposure to a higher level of BA was decreased following EBL treatment. Thus, this study showed that the exogenous application of EBL ameliorates the toxic effects of B in a model plant by improving the plant’s antioxidant system and decreasing B accumulation. To our knowledge, this is the one of the first studies to examine the effect of BR in plants subjected to B toxicity.     

Ameliorative Role of Pre-Sowing Proline Treatment in <i>Coriandrum sativum</i> L. Seedlings under Mercury Toxicity

Heavy metal toxicity is one of the major ecosystem concerns globally in present time and is also responsible for significant threat to agronomic crops. The current work was conducted to investigate the possible ameliorative role of proline in Coriandrum sativum L. seedlings treated with mercury (Hg). The seedlings were exposed to different concentrations of Hg (0, 0.1, 0.3 and 0.5 mM) for 20 days. The effects of pre-sowing treatment with proline were studied on C. sativum seedlings in terms of pigment (chlorophylls, carotenoids and anthocyanins), malondialdehyde (MDA), antioxidant compound (glutathione, total phenolic compounds, ascorbic acid) and osmolytes (proline, glycine betaine). Additionally, activities of antioxidant enzymes, namely catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) were also studied. A strong decline of photosynthetic pigment concentrations was observed in leaves of C. sativum under Hg toxicity. Treatment of seeds with proline reduced the loss of photosynthetic pigments, counteract Hg-triggered oxidative stress, likely preserving the functionality of antioxidant apparatus under Hg stress. The increment of total polyphenols and glycine betaine also contributed in ameliorating Hg toxicity, suggesting the use of exogenous proline as a potential method to enhance the plant tolerance against heavy metal stress.     

Applications of ascorbic acid or proline increase resistance to salt stress in barley seedlings

The present study was carried out to examine the effects of seed soaking in 1 mM ascorbic acid (AA) or 1 mM proline on the growth, content of photosynthetic pigments and proline, relative water content, electrolyte leakage, antioxidant enzymes and leaf anatomy of Hordeum vulgare L. Giza 124 seedlings grown in greenhouse under 100 or 200 mM NaCl. The plants exposed to the NaCl stress exhibited a significant reduction in growth, relative water content, leaf photosynthetic pigments, soluble sugars, as well as alterations in leaf anatomy. However, the treatment with AA or proline ameliorated the stress generated by NaCl and improved the above mentioned parameters. NaCl increased electrolyte leakage, proline content, and activities of antioxidant enzymes (SOD, CAT, and POX). The antioxidant enzymes and leaf anatomy exhibited considerable changes in response to AA or proline application in the absence or presence of NaCl.     

Effect of 24-epibrassinolide on oxidative stress markers induced by nickel-ion in <Emphasis Type="Italic">Raphanus sativus</Emphasis> L.

The present study illustrates the effect of 24-epibrassinolide (24-EBL) on morphological and biochemical parameters in radish (Raphanus sativus L.) seedlings grown under nickel (Ni) ion stress. The radish seeds pre-soaked in different concentrations of 24-EBL were sown in petridishes containing various concentrations of heavy metal (Ni).Observations were made on root/shoot length, fresh biomass, activities of antioxidant enzymes (ascorbate peroxidase, superoxide dismutase, catalase, monodehydroascorbate reductase, dehydroascorbate reductase, guaiacol peroxidase and glutathione reductase), lipid peroxidation, proline and protein content in 7-day-old Ni-stressed radish seedlings. Results indicate that seeds presoaked with 24-EBL reduced the impact of Ni-stress which was evident by assessing the morphological parameters, protein content and antioxidant enzyme activities. It was also observed that 24-EBL reduced the toxicity of heavy metal by influencing proline and malondialdehyde (MDA) content. The present study lays a foundation for understanding the role of 24-EBL in heavy metal stress amelioration, particularly in food crop. Analysis of behaviour of antioxidant enzymes will play a critical role in understanding the stress networking, further filling the knowledge gap on the subject.     

Combined action of antioxidant defense system and osmolytes in chilling shock-induced chilling tolerance in Jatropha curcas seedlings

Low non-freezing temperature is one of the major environmental factors affecting growth, development and geographical distribution of chilling-sensitive plants, Jatropha curcas is considered as a sustainable energy plants with great potential for biodiesel production. In this study, chilling shock at 5 °C followed by recovery at 26 °C for 4 h significantly improved survival percentage of J. curcas seedlings under chilling stress at 1 °C. In addition, chilling shock could obviously enhance the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR), and the levels of antioxidants ascorbic acid (AsA) and glutathione (GSH), as well as the contents of osmolytes proline and betaine in leaves of seedlings of J. curcas compared with the control without chilling shock. During the process of recovery, GR activity, AsA, GSH, proline and betaine contents sequentially increased, whereas SOD, APX and CAT activities gradually decreased, but they markedly maintained higher activities than those of control. Under chilling stress, activities of SOD, APX, CAT, GR and GPX, and contents of AsA, GSH, proline and betaine, as well as the ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)] in the shocked and non-shock seedlings all dropped, but shocked seedlings sustained significantly higher antioxidant enzyme activity, antioxidant and osmolyte contents, as well as ratio of reduced antioxidants to total antioxidants from beginning to end compared with control. These results indicated that the chilling shock followed by recovery could improve chilling tolerance of seedlings in J. curcas, and antioxidant enzymes and osmolytes play important role in the acquisition of chilling tolerance.     

Selenium mitigates cadmium-induced oxidative stress in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis> L.) plants by modulating chlorophyll fluorescence,osmolyte accumulation,and antioxidant system

Pot experiments were conducted to investigate the role of selenium in alleviating cadmium stress in Solanum lycopersicum seedlings. Cadmium (150 mg L^?1) treatment caused a significant reduction in growth in terms of height and biomass accumulation and affected chlorophyll pigments, gas exchange parameters, and chlorophyll fluorescence. Selenium (10 μM) application mitigated the adverse effects of cadmium on growth, chlorophyll and carotenoid contents, leaf relative water content, and other physiological attributes. Lipid peroxidation and electrolyte leakage increased because of cadmium treatment and selenium-treated plants exhibited considerable reduction because of the decreased production of hydrogen peroxide in them. Cadmium-treated plants exhibited enhanced activity of antioxidant enzymes that protected cellular structures by neutralizing reactive free radicals. Supplementation of selenium to cadmium-treated plants (Cd + Se) further enhanced the activity of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) by 19.69, 31.68, 33.14, and 54.47%, respectively. Osmolytes, including proline and glycine betaine, increased with selenium application, illustrating their role in improving the osmotic stability of S. lycopersicum under cadmium stress. More importantly, selenium application significantly reduced cadmium uptake. From these results, it is clear that application of selenium alleviates the negative effects of cadmium stress in S. lycopersicum through the modifications of osmolytes and antioxidant enzymes.     

丛枝菌根真菌对盐胁迫下黄瓜幼苗渗透调节物质含量和抗氧化酶活性的影响

以盐敏感型黄瓜品种‘津春2号’为材料,研究了丛枝菌根真菌(AMF)对盐胁迫下黄瓜幼苗生长及叶片、根系中渗透调节物质含量和抗氧化酶活性的影响.结果表明:(1)在盐胁迫条件下,黄瓜幼苗生长受到明显抑制,其株高、地上部、地下部干鲜重均明显减小,同时体内可溶性蛋白、可溶性糖、脯氨酸和MDA含量,以及O2(÷)产生速率和SOD、POD、CAT活性均比对照显著升高.(2)盐胁迫下接种AMF可显著促进黄瓜植株的生长,进一步提高黄瓜幼苗体内可溶性蛋白、可溶性糖和脯氨酸含量及SOD、POD、CAT活性,而显著降低MDA含量和O2(÷)产生速率.研究表明,AMF可通过显著促进盐胁迫下黄瓜幼苗体内渗透调节物质积累和抗氧化酶活性提高,有效降低体内膜脂过氧化水平,从而缓解盐胁迫对植株的伤害,增强黄瓜幼苗对盐胁迫的耐性.     

叶绿酸铁对亚适温条件下黄瓜幼苗渗透调节物质及抗氧化酶活性的影响

以黄瓜品种“津研四号”为试材,利用光照培养箱进行亚适温处理(昼/夜18/12 ℃),研究亚适温条件下喷施5 mg·L^-1叶绿酸铁溶液对黄瓜幼苗生长、脯氨酸、可溶性糖、丙二醛含量及抗氧化酶活性的影响.结果表明: 亚适温条件下叶面喷施叶绿酸铁可以缓解亚适温对黄瓜生长的抑制,增加叶片中脯氨酸和可溶性糖含量,减少丙二醛含量,提高超氧化物歧化酶、过氧化物酶、过氧化氢酶及抗坏血酸过氧化物酶活性.喷施叶绿酸铁在一定程度上可通过促进渗透调节物质的积累和提高抗氧化酶活性,来降低膜脂质过氧化水平,从而增强黄瓜幼苗对亚适温的适应性.     

Accumulation of hydrogen peroxide and functioning of defense system in overwatered barley seedlings

The effects of overwatering (flooding) on the oxidative potential, the level of low-molecular-weight antioxidants, the content of stress proteins, and activities of antioxidant enzymes in green barley (Hordeum vulgare L.) seedlings were studied. Overwatering retarded barley seedling growth and induced hydrogen peroxide accumulation, a decrease in the total ascorbate content and an increase in the content of reduced glutathione (GSH), but it did not affect the content of oxidized glutathione (GSSG). After the cessation of stress factor action (post-stress period), the content of hydrogen peroxide declined to the initial level, the content of ascorbate reduced still stronger, whereas the content of GSH continued to rise. Under flooding conditions, activities of glutathione reductase (GR) and superoxide dismutase (SOD) increased. After the cessation of stress factor action, activities of these enzymes decreased but remained at rather high levels as compared with control. Activity of catalase (CAT) reduced during stress, whereas activity of ascorbate peroxidase (APX) was not essentially changed. In the post-stress period, CAT activity remained to be low; in contrast, APX activity increased. Barley seedling flooding induced the synthesis of stress proteins, HSP70 and dehydrins (DH). In the post-stress period, the content of stress proteins decreased; however, the content of DH in experimental leaves remained rather high. The results obtained indicate that barley defense system manifested a complex response to overwatering, which may be related to the oxygen shortage under stress conditions and sharp metabolism activation at re-aeration in the post-stress period.     

Responses of Wheat Seedlings to Exogenous Selenium Supply Under Cold Stress

Dose-dependent effects of selenium on growth and physiological trait of wheat seedlings (Triticum aestivum L. cv Han NO.7086) exposed to cold stress are reported. Responses of seedlings were different depending on the Se concentration. The treatments with 0.5 and 1.0 mg Se kg⁻¹ significantly increased biomass and chlorophyll content of seedlings. However, the treatments at 2.0 and 3.0 mg Se kg⁻¹ only induced an evident increase in chlorophyll content and did not promote biomass accumulation of seedlings. Antioxidant compounds content (anthocyanins, flavonoids, and phenolic compounds) and antioxidant enzymes’ activities (peroxidase and catalase) increased by different Se treatments, while only the treatment with 1.0 mg Se kg⁻¹ induced a significant reduce in malondialdehyde content and the rate of superoxide radical production of wheat seedlings. The results of this study demonstrated that Se supply could increase antioxidant capacity of seedlings, and optimal Se supply reduced production of free radicals, membrane lipid peroxidation, and promoted biomass accumulation.     

Effects of exogenous nitric oxide on cadmium toxicity, element contents and antioxidative system in perennial ryegrass

The effects of sodium nitroprusside (SNP, a donor of NO) on cadmium (Cd) toxicity in ryegrass seedlings (Lolium perenne L.) were studied by investigating the symptoms, plant growth, chlorophyll content, lipid peroxidation, H⁺-ATPase enzyme and antioxidative enzymes. Addition of 100???M CdCl₂ caused serious chlorosis and inhibited the growth of ryegrass seedlings, and dramatically increased accumulation of Cd in both shoots and roots, furthermore, the absorption of macro and micronutrients were inhibited. Addition of 50, 100, 200???M SNP significantly decreased the transport of Cd from roots to shoots, alleviated the inhibition of K, Ca, Mg and Fe, Cu, Zn absorption induced by Cd, reduced the toxicity symptoms and promoted the plant growth. The accumulation of reactive oxygen species (ROS) significantly increased in ryegrass seedlings exposed to Cd, and resulted in the lipid peroxidation, which was indicated by accumulated concentration of thiobarbituric acid-reactive substances. Addition of 50, 100, 200???M SNP significantly decreased the level of ROS and lipid peroxidation. Activities of antioxidant enzymes also showed the same changes. Addition of 50, 100, 200???M SNP increased activities of superoxide dismutase, peroxidase, catalase and ascorbate peroxidase in ryegrass seedlings exposed to Cd. Addition of 100???M SNP had the most significant alleviating effect against Cd toxicity while the addition of 400???M SNP had no significant effect with Cd treatment.     

Effects of Calcium and Calmodulin Antagonists on Chilling Stress-Induced Proline Accumulation in <Emphasis Type="Italic">Jatropha curcas</Emphasis> L.

Regulation of proline accumulation in plants under chilling stress remains unclear. In this paper, we treated Jatropha curcas seedlings under chilling stress with exogenous calcium chloride (CaCl₂), the plasma membrane Ca²⁺-channel blocker lanthanum chloride (LaCl₃), calmodulin antagonists, chlorpromazine (CPZ), and trifluoperazine (TFP) and investigated the effects of calcium and calmodulin (CaM) on proline accumulation and chilling tolerance. The results showed that CaCl₂ treatment significantly enhanced chilling stress-induced proline accumulation. CaCl₂ also induced an almost immediate and rapid increase of Δ¹-pyrroline-5-carboxylate synthetase (P5CS) and glutamate dehydrogenase activities, the key enzymes in the glutamate pathway of proline biosynthesis, and up-regulated P5CS expression, but it decreased the activity of proline dehydrogenase (ProDH), a key enzyme of proline degradation, and inhibited ProDH expression. Treatment with LaCl₃, CPZ, and TFP exhibited the opposite effects to those by CaCl₂ treatment. Moreover, CaCl₂, LaCl₃, CPZ, and TFP had little effect on the activities of ornithine aminotransferase and arginase, the key enzymes in the ornithine pathway of proline biosynthesis. These results indicated that Ca²⁺-CaM might be involved in signal transduction events, leading to proline accumulation in J. curcas seedlings under chilling stress, and that Ca²⁺-induced proline accumulation is a combined result of the activation of the glutamate pathways of proline biosynthesis and the simultaneous inhibition of the proline degradation pathway. In addition, CaCl₂ treatment increased tissue vitality, decreased the content of the lipid peroxidation product malondialdehyde (MDA), and alleviated electrolyte leakage in J. curcas seedlings under chilling stress, indicating that exogenous Ca²⁺ can enhance chilling tolerance, and proline might be a key factor in this increased chilling tolerance.