Boron stress,oxidative damage and antioxidant protection in potato cultivars (Solanum tuberosum L.)

Six potato cultivars grown in Turkey in boron-prone areas and differing in their tolerance towards high boron were studied to reveal whether boron causes oxidative stress. To assess stress level, chlorophyll fluorescence and growth parameters were measured. Oxidative damage was assessed as malondialdehyde level, and antioxidant protection was evaluated as ascorbate (AA), dehydroascorbate, reduced glutathione (GSH) and oxidized glutathione amounts and superoxide dismutase, catalase, ascorbate peroxidase (APX) and glutathione reductase (GR) activities. High boron stress affected photosynthesis negatively in a threshold-dependent manner and inhibited growth. No pronounced changes in oxidation of lipids occurred in any cultivar. Activation of APX suggested the involvement of an ascorbic acid–reduced glutathione cycle in the protection against oxidative stress caused by high boron. Efficient work of this antioxidant system was probably hindered by boron complexation with NAD(P)⁺/NAD(P)H and resulted in the inhibition of GR and a decrease in AA and GSH. Hence, oxidative stress associated with high boron is a secondary component of boron toxicity which arises from metabolic changes caused by boron interference with major metabolites. Potato cultivars tolerate excess boron stress well and show damage only in very high boron concentrations. The potato cvs best suited for high boron soils/breeding purposes are cvs Van Gogh and Agria.

Abbreviations: AA: ascorbic acid; APX: ascorbate peroxidase; CAT: catalase; DHA: dehydroascorbic acid; DHAR: dehydroascorbate reductase; DTNB: 5; 5′-dithiobis-2-nitrobenzoic acid; DTT: dithiotreitol; F_v/F_m: photosynthetic efficiency at the dark-adapted state; GR: glutathione reductase; GSH: reduced glutathione; GSSG: oxidized glutathione; MDA: malondialdehyde; ROS: reactive oxygen species; SOD: superoxide dismutase; TCA: trichloroacetic acid     

Nitrogen to sulphur ratio in rapeseed and in rapeseed protein and its use in diagnosing sulphur deficiency

This study investigated the variation of nitrogen to sulphur ratios in rapeseed (N/S)_t and in rapeseed protein (N/S). Under S‐sufficient conditions the (N/ S)_t ratios varied considerably between different varieties, with low glucosinolate varieties having higher ratios than high glucosinolate varieties. In contrast, (N/S)_p remained relatively constant at about 11.5 for all varieties tested, though significant effects of N and S nutrition on the (N/S) ratio were present. The ratio increased in the S‐deficient samples. Results of yield responses to S fertilizer and (N/S)₍from six field experiments were used to see if (N/S)_t could indicate the S status of the crop. Although yield losses due to S shortage tended to occur when (N/S)_t was greater than 10, the relationship was not sufficiently reliable for use in diagnosis.     

Drought stress-induced oxidative stress and antioxidative responses in four wheat (Triticum aestivum L.) varieties

Drought stress was imposed on four varieties of wheat (Triticum aestivum L.), Mohan Wonder (MW), Kedar (K), Gayetri (GY) and Gandhari (GN), for 3, 6 and 9 days. The activities of all five tested antioxidative enzymes, peroxidase, ascorbate peroxidase, catalase, glutathione reductase and superoxide dismutase, were enhanced initially in varieties K and GN, whereas in MW and GY, catalase and superoxide dismutase showed a decrease in activity at all periods of drought stress. Peroxidase and glutathione reductase activities increased even on the ninth day of stress in K and GN, but all other activities showed a decrease after 3 days of stress. H₂O₂ accumulation increased with drought stress, but in K and GN there was decrease during prolonged drought stress. Lipid peroxidation increased significantly due to drought stress, which was higher in the case of MW and GY. Proline, phenol and ascorbate content increased with period of drought stress. Carotenoid accumulation also increased initially. Total chlorophylls showed a general decrease during drought stress. The results of this study indicate that two of the varieties, MW and GY, are susceptible to drought stress, whereas the other two, K and GN, are tolerant, with peroxidase and glutathione reductase being most important in conferring tolerance.     

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.     

The Cd‐tolerant rice mutant cadH‐5 is a high Cd accumulator and shows enhanced antioxidant activity

To investigate the mechanism of cadmium (Cd) detoxification in rice (Oryza sativa L.), a Cd‐tolerant mutant cadH‐5, obtained by an Agrobacterium tumefaciens‐based gene‐delivery system, was used for a Cd‐tolerance and accumulation study. After 15 d of exposure to 0.75 mM CdCl₂, significant phenotypic differences were observed between the wild type (WT) and cadH‐5. When exposed to 0.5 mM CdCl₂, higher Cd levels were accumulated in cadH‐5 root cell wall, root cytosol, and membranes than those in WT. However, Cd concentrations in root tissues varied in both WT and cadH5. No significant difference of hydrogen peroxide (H₂O₂) concentrations was observed between WT and cadH‐5, while contents of cell‐wall polysaccharides and phytochelatins (PCs) in the mutant were higher compared to WT. The ratios of reduced glutathione to oxidized glutathione (GSH : GSSG) and ascorbate to dehydroascorbate (ASC : DHA) were lower in WT than in cadH‐5, while the NADPH : NADP⁺ ratio was different to the ratios of GSH : GSSG and ASC : DHA; the ascorbate peroxidase (APX, EC 1.11.1.11), glutathione peroxidase (GR, EC 1.6.4.2), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities were lower in WT compared to cadH‐5. Our results indicate that under long‐term Cd stress, cadH‐5 plants can accumulate more Cd with more PC. Also, the redox status of ASC‐GSH cycle was more inhibited in WT than in cadH‐5 plants, rendering WT less able to scavenge reactive oxygen species (ROS). The cadH‐5 mutant maintains relatively high ASC, GSH, and NADPH concentrations, ratios of ASC : DHA, GSH : GSSG, and NADPH : NADP⁺, as well as antioxidative enzymatic activities and PC concentrations. Thus, it is tolerant of relatively high Cd accumulation.     

The effect of foliar applied sulphur on individual glucosinolates in oilseed rape seed

The effect of foliar applied elemental sulphur on the individual glucosinolate content of oilseed rape seed was studied. Results show that the proportions of individual glucosinolates remained stable despite changes in the amount of sulphur applied, indicating that controlling sulphur availability cannot be used as a management tool to reduce the toxicity of rapeseed meal.     

Significance of sulfur in heat stressed cluster bean (Cymopsis tetragonoloba L. Taub) genotypes: responses of growth,sugar and antioxidative metabolism

A sand culture experiment was carried out to study the effects of sulfur deprivation on heat stress tolerance of two cluster bean (Cymopsis tetragonoloba L. Taub) cultivars (GC-1 and Pusa Nau Bahar (PNB)). Three weeks old sulfur-starved and sulfur-supplemented plants were subjected to heat stress (45°C/35°C) treatment for 24 h. Total dry weight, chlorophyll content, Chlorophyll a:b ratio, electrolyte leakage, malondialdehyde (MDA) accumulation, H₂O₂ content, sugar, glucose-6-phosphate (G-6-P), fructose-6-phosphate (F-6-P), ascorbate and glutathione concentrations and antioxidant enzyme activity (superoxide dismutase (SOD) and catalase (CAT)) were monitored, at the end of the heat stress treatment. Heat stress enhanced and sulfur starvation depleted the contents of sugar metabolites, but the accumulation of sugar, G-6-P and F-6-P were not related with heat stress tolerance. Antioxidant enzyme activities of SOD and CAT were influenced significantly more by sulfur starvation than heat stress. The results showed that under heat stress, the addition of sulfur helps to mitigate the oxidative damage in both the cultivars. However, GC-1 was more heat tolerant as it was characterized by significantly higher total dry weight, chlorophyll content, ascorbate and glutathione content and lower H₂O₂, MDA, electrolyte leakage than PNB.     

The Effects of Sulphur Application on Yield,Sulphur Content and N/S-Ratio of Grasses for Silage at Six Sites in Finland

Abstract

The effects of sulphur (S) fertilization on forage production, sulphur content and N/S ratio of perennial timothy-meadow-grass (Phleum pratens L.- Festuca pratensis Hudson) and cocksfoot-dominant (Dactylis glomerata L.) swards cropped for one to three years were measured under a silage-cutting regime at six sites in Finland. Soil sulphur status ranged from poor/adequate (fine sand) to good (organic soils). Plant growth responses to supplementary sulphur were small, inconsistent and statistically insignificant. The supplementary S-fertilization increased the sulphur content of forage and decreased N/S-ratios at all sites. However, even in low-S fertilized plots the average sulphur content was very seldomly less than 0.2% on a dry matter (DM) basis, which has been assumed to be an adequate concentration in several foreign studies. High N/S ratios (> 14) were rare. The sulphur content of DM depended more significantly on growth stage and grass species than on supplementary sulphur. According to the results of these experiments, NPKS fertilizers contain sufficient amounts of sulphur to ensure both a good quality and a high yield of grass silage.     

Responses of Components of Antioxidant System in Moongbean Genotypes to Cadmium Stress

Four genotypes (Pusa 9531, Pusa 9072, Pusa Vishal, PS‐16) of moongbean [Vigna radiata (L.) Wilczek] grown in earthen pots were treated with cadmium at 0, 25, 50, and 100 mg kg^?1 soil. Cadmium tolerance (CdT), the ability of a plant to maintain growth at high levels of cadmium (Cd), was calculated as the ratio of dry‐matter production in the untreated and the Cd‐treated soils. The moongbean genotypes showed a differential response to Cd concentrations; Pusa 9531 was identified as Cd tolerant, whereas PS 16 was Cd susceptible. To find out the physiological basis of these differences, we investigated the possible role of antioxidant (enzymatic and nonenzymatic) defense systems. Activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), ascorbate peroxidase (EC 1.11.1.11), and glutathione reductase (EC 1.6.4.2) and the amounts of ascorbate and glutathione were monitored in the Cd‐tolerant and Cd‐sensitive moongbean genotypes. The results revealed the presence of a strong antioxidant defense system in the Cd‐tolerant genotype (Pusa 9531) for providing adequate protection against oxidative stress caused by Cd.     

A study on the effect of cadmium on the antioxidative defense system and alteration in different functional groups in castor bean and Indian mustard

The present study was planned to delineate the role of antioxidants and different functional groups of Ricinus communis and Brassica juncea in the tolerance mechanisms toward cadmium (Cd) for phytoremediation. Application of Cd caused a reduction in dry biomass of 53.84% and 26.58% in root and 45.33% and 33.84% in shoots of B. juncea and R. communis, respectively. Antioxidant enzymes, namely superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and glutathione-S-transferase, and metabolites (proline) increased in both the species due to Cd exposure. The metal caused substantial changes in the functional groups present in the roots and leaves of the plants. A number of new peaks appeared in the Cd-treated plants, which indicate the production of the compounds responsible for the metal tolerance of these plants. R. communis has been found to possess a good antioxidant defense system against Cd stress and may be used for the phytoremediation of metal-contaminated soils in place of edible crops, which enhance the risk of contaminating the food chain. It has been observed that R. communis accumulated 213.39 and 335.68 mg Cd in roots and shoots, respectively, whereas B. juncea accumulated 28.19 and 310.15 mg Cd in the roots and shoots, respectively.     

Sulfur content of plant material: A comparison of methods of oxidation prior to determination

Abstract

Procedures for S determination involving digestion of plant material with HNO₃/HClO₄ mixtures gave lower values than those using oxygen flask combustion. Tests on a range of S compounds showed that the HNO₃/HClO₄ procedure underestimated S present in methionine, cysteine and glutathione but S in sulfate and the glucosinolate, sinigrin, was not underestimated.

Low recoveries using HNO₃/HClO₄ digestion procedures can be due both to incomplete oxidation of certain compounds and to gaseous losses during the vigorous boiling stage of digestion.     

发芽绿豆苗的生理指标和抗氧化特性对邻苯二甲酸酯的响应特征

Single phytotoxicity of two representative phthalate esters （PAEs）, di-n-butyl phthalate （DnBP） and bis（2-ethylhexyl） phthalate （DEHP）, was tested in mung bean （Vigna radiata） seedlings germinated for 72 h in soils spiked with varying concentrations （0-500 mg kg-1 soil） of DnBP or DEHP. PAEs added at up to 500 mg kg-1 soil exerted no significant effect on germination but both pollutants significantly inhibited root elongation （P 〈 0.01）; DEHP inhibited shoot elongation （P 〈 0.01） and DnBP depressed biomass on a fresh weight basis （P 〈 0.05）. Seedling shoot and root malondialdehyde （MDA） Contents tended to be stimulated by DnBP but inhibited by DEHP. However, increases in superoxide dismutase, peroxidase, ascorbate peroxidase and polyphenol oxidase activities, as well as glutathione （GSH） content, were induced at higher concentrations （e.g., 20 mg kg-1） of both compounds. Accumulation of proline in both roots and shoots and the storage compounds, such as free amino acids and total soluble sugars, in whole plant was induced under the stress exerted by both PAEs. The general responses of mung bean seedlings indicated higher toxicity of DnBP than DEHP on primary growth, during which root elongation was a more responsive index. MDA and GSH were more sensitive parameters in the roots than in the shoots and they might be recommended as physiologically sensitive parameters to assess the toxicity of PAE compounds in soils in future long-term studies.     

籽粒硫苷特性对甘蓝型油菜吸收积累Cd的影响

油菜对Cd的吸收转运不仅受外源S供应的影响,且与自身S代谢关系非常密切。硫苷是影响油菜品质的重要含S次级代谢产物,而油菜籽粒硫苷含量能较好地表征油菜的硫苷特性。为了解油菜硫苷特性与油菜吸收积累Cd之间的关联,通过Cd污染土壤的大田试验,研究了不同硫苷特性甘蓝型油菜的Cd吸收积累特性。结果表明,初花期高、低硫苷油菜不同器官间Cd含量皆为根叶茎,成熟期皆为茎根壳籽粒。初花期高硫苷与低硫苷油菜对Cd的吸收积累无显著差异;而成熟期高硫苷油菜对Cd的吸收积累显著低于低硫苷油菜,高硫苷油菜成熟期根、茎、壳、籽粒Cd含量分别为3.90 mg?kg?1、4.50 mg?kg?1、0.97 mg?kg?1、0.17 mg?kg?1,低硫苷油菜则分别为4.57 mg?kg?1、5.20 mg?kg?1、1.32 mg?kg?1、0.29 mg?kg?1,比高硫苷油菜分别高17.18%(P0.05)、15.56%(P0.05)、36.08%(P0.05)、70.59%(P0.05)。成熟期高硫苷油菜壳/茎、籽粒/壳Cd转运系数分别为0.22和0.17,而低硫苷油菜分别为0.25和0.23,比高硫苷油菜分别高13.64%(P0.05)和35.29%(P0.05)。高硫苷油菜显著抑制了Cd从茎向其上位器官(壳、籽粒)的转运。研究结果还表明,低硫苷油菜与高硫苷油菜对污染土壤Cd的单季净化率分别仅为0.90%和0.76%,作为修复Cd污染土壤的富集植物,其净化效率皆有待提高。     

Derivation of diagnostic indices for assessing the sulphur status of Panicum maximum var. trichoglume

Abstract

The effects of nitrogen fertilization and age of regrowth on a number of indices for assessing the sulphur status of the perennial tropical pasture grass Panicum maximum var. trichoglume (green panic) have been examined in pot experiments. A non‐rectangular hyperbola regression model has been used as an aid in deriving critical sulphur concentrations and evaluating their confidence limits. The merits and limitations of this model together with problems associated with other methods of deriving critical nutrient concentrations are discussed.

Results indicate that critical total S concentrations in whole plant tops declined markedly with age of regrowth. Critical sulphate S concentrations were more stable with age of regrowth, concentrations in excess of 0.012% being indicative of adequate sulphur for maximum plant yield. It is also suggested that plants have adequate sulphur when more than 12% of their total S content is in the sulphate form. N:S ratios may provide a useful guide for assessing sulphur status but should be treated with caution when the nitrogen supply to the plants is high.     

Effect of nitrogen and sulphur fertilization on the yield and composition of winter oilseed rape

Abstract

A field experiment was conducted to assess the effects of varying levels of sulphur (S) and nitrogen (N) supply on oilseed rape (Brassica napus L. var. Rafal) grown in a soil assessed to be in the low category for plant available sulphate (SO₄). There were no significant effects on crop yield as a result of applied S for any of the treatments. This was probably due to a significant input of atmospheric S as a result of the wetter than average year. However, there were significant compositional effects on total S, total N and sulphate‐sulphur (SO₄‐S) which has implications for the supply of S from soil which can often display a range of S availabilities. Effects on composition were most marked as the crop reached maturity.     

Salicylic acid improves the antioxidant ability against arsenic-induced oxidative stress in sunflower (Helianthus annuus) seedling

The present study investigated the potential role of external salicylic acid (SA) in alleviating Arsenic (As) toxicity in sunflower leaves. The exposure of plants to 10 µM As inhibited biomass production and intensively increased the accumulation of As in both roots and leaves. The levels of some important parameters associated with oxidative stress, namely lipid peroxidation, electrolyte leakage, and hydrogen peroxide (H₂O₂) production were increased. SA application alleviated the negative effect of As on growth and led to decrease in oxidative injuries. Furthermore, SA application led to higher activity of catalase, ascorbate peroxidase, and glutathione peroxidase, and concomitantly decreased superoxide dismutase and guaiacol peroxidase activities. As important antioxidants, ascorbate and glutathione contents in sunflower leaves exposed to As were significantly decreased by SA treatment. These results reveal that SA is more effective in alleviating As toxicity at higher concentrations than that at lower concentrations.     

Sensitivity of forest-floor mosses in boreal forests to nitrogen and sulphur deposition

The response of forest-floor mosses to deposition of nitrogen (N) and sulphur (S) was examined in field conditions in a 60-year-old Norway spruce (Picea abies Karst.) stand in southern Finland. The experimental plots received nitrogen (25 kg N ha^–1) and sulphur (30 kg S ha^–1) as ammonium sulphate once a year for 4 years.The dominant moss species on the site were Pleurozium schreberi (Mitt.) and Dicranum polysetum (Sw.). The biomass of the dominant moss species was decreased significantly by N and S deposition during the study period. Due to the addition of N and S, the biomass of Pleurozium schreberi was decreased by 60% and the biomass of Dicranum polysetum by 78%.     

Effect of combined nitrogen and sulphur fertilization on yield and qualitative parameters of Camelina sativa [L.] Crtz. (false flax)

Abstract

Camelina (Camelina sativa (L.) Crtz., false flax) is described as a species requiring fewer inputs than other oilseed crops thus making it an interesting alternative in sustainable cropping systems. As information on the combined effects of nitrogen and sulphur on camelina yield and quality parameters is meagre, a pot fertilization experiment was carried out with nitrogen applied as NH₄NO₃ at three increasing rates equivalent to a range from 63 up to 127 kg ha^?1. These treatments were combined with sulphur additions applied as (NH₄)₂SO₄ to achieve a soil sulphate content of 25 or 45 mg kg^?1, respectively (equivalent to 75 and 135 kg S ha^?1). The medium and high nitrogen rates combined with the low sulphur fertilization level increased the number of branches per plant compared with the lowest nitrogen fertilization at the same sulphur rate. Camelina seed yield increased with increasing nitrogen doses at the same low sulphur level, whereas straw yield increased only at the highest rate of nitrogen. Thousand-seed mass increased at the highest nitrogen dose and with the low sulphur application rate. In addition, the increase in nitrogen fertilization reduced seed oil content from 39.8% to 37.1%. A highly negative correlation was observed between oil and protein content of seeds. Nitrogen fertilization increased total oil yield and total protein yield. Differences in crop parameters between the sulphur treatments were not significant statistically, although the higher sulphur treatment tended to increase seed yield as well as oil and protein content compared with the low sulphur treatment. Thus, the combined application of N and S as mineral fertilizers is only recommended when growing camelina on sulphur-deficient soils if the aim is to achieve both high oil and protein production.     

Aspergillus flavus transformation of glucosinolates to nitriles by an arylsulfatase and a β-thio-glucosidase

Biofumigation is a biocontrol method that uses volatile compounds to combat soil pathogens. We investigated a biofumigation process based on the green manure of Brassicaceae. These plants contain the glucosinolate-myrosinase system which releases inhibitory compounds such as isothiocyanate into the soil. However, the biocontrol effectiveness is often lower than expected, possibly due to microbial transformation of the isothiocyanates. In order to identify the possible function of microorganisms, their interaction with glucosinolates and glucosinolate-derived products was investigated. We report the ability of a soil isolate of Aspergillus flavus to grow in liquid culture and convert 2-propenyl and 2-phenylethyl glucosinolate and their desulfo-derivatives, to nitriles. This finding would suggest the existence of an arylsulfatase and a β-thio-glucosidase, different from myrosinase, which could direct glucosinolate conversion in soil towards nitriles rather than isothiocyanates. If confirmed in soil, our observations could at least partially explain the low concentrations of isothiocyanates after biofumigation.     

Nickel toxicity in two durum wheat cultivars differing in drought sensitivity

The effects of nickel (Ni) on growth, leaf water status, and mineral nutrient concentration were studied in two wheat (Triticum durum Desf.) cultivars with different sensitivity to water stress: ‘Adamello’ [drought sensitive (DS)] and ‘Ofanto’ [drought tolerant, (DT)]. The DT cultivar showed a higher Ni absorption capacity: ‘Ofanto’ seedlings grown in the presence of 35 μM Ni had a 3.5 times greater concentration of Ni in roots than did ‘Adamello’. Despite the greater Ni tissue content, the DT cultivar exhibited better growth and nutritional status when compared to the DS cultivar. In the DS cultivar the concentration of chlorophyll a and b was reduced by Ni treatment. Chlorophyll a concentration decreased in the DT cultivar, but to a lesser extent than in the DS cultivar; chlorophyll b was not altered by Ni level in the DT cultivar. Nickel caused a decrease in the water potential (ψ_w) and relative water content (RWC) in both cultivars, but these decreases were greater in the DS cultivar. The antioxidative defense enzymes, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase, showed increased activity in Ni‐treated DS seedlings; this increase in activity was not observed in the DT seedlings. These data suggest that different wheat genotypes may markedly differ in Ni uptake and sensitivity and that a enhanced capacity to counteract Ni stress may be associated with drought resistance.