Sulfur stress-induced antioxidative responses in leaves of Triticum aestivum L.

Antioxidative responses were investigated in leaves of wheat (Triticum aestivum L.) grown at varying S levels ranging from deficiency to excess (1, 2, 4, 6 and 8 mM S). Optimum yield was observed in plants supplied with 4 mM S. Wheat responded to S deficiency and excess supply by decreasing growth of root and shoot. Chlorosis in young leaves was observed after 15 days of deficient S supply. The biomass and concentration of photoassimilatory pigments decreased in plants grown at 1, 2, 6 and 8 mM S supply. The concentration of thiobarbituric acid reactive substances (TBARS), cysteine, nonprotein thiol and hydrogen peroxide (H₂O₂) increased in plants grown under S stress. Accumulation of TBARS and H₂O₂ in leaves indicated oxidative damage in S-deficient and S-excess plants. Deficient and excess levels of S showed an increase in the activities of antioxidative enzymes superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2).     

Effect of zinc nutritional status on activities of superoxide radical and hydrogen peroxide scavenging enzymes in bean leaves

The effect of varied zinc (Zn) supply on the activities of superoxide dismutase (SOD), ascorbate (AsA) peroxidase, glutathione (GSSG) reductase, catalase and guaiacol peroxidase was studied in leaves of bean (Phaseolus vulgaris) plants grown for 15 days in nutrient solution. Zinc deficiency severely decreased plant growth and the leaf concentrations of soluble protein and chlorophyll. Resupply of Zn to deficient plants for up to 72h restored protein concentrations more rapidly than chlorophyll and plant growth. With the exception of guaiacol peroxidase, the activities of all enzymes were significantly decreased by Zn deficiency, in particular GSSG reductase and SOD. Within 72h of resupplying Zn to deficient plants, the enzyme activities reached the level of the Zn sufficient plants. The results indicate severe impairment in the ability of Zn-deficient leaves to enzymically scavenge O₂ ^- and H₂O₂. Consequences and reasons of this impairment are discussed in terms of photooxidation of chloroplast pigments and inhibition of the biosynthesis of the related scavenger enzyme proteins.     

The effect of zinc stress combined with high irradiance stress on membrane damage and antioxidative response in bean seedlings

Zinc (Zn) is a necessary element for plants, but excess Zn can be detrimental. The effect of Zn and high irradiance (HI) stress on the growth, lipid peroxidation (MDA), membrane permeability (EC), hydrogen peroxide (H₂O₂) accumulation, non-enzymatic antioxidants like proline accumulation and ascorbic acid (AsA) and the activities of major antioxidant enzymes (superoxide dismutase, SOD; peroxidase, POX; polyphenol oxidase, PPO) of bean leaves were investigated under controlled growth conditions. The root length was not reduced at excess Zn level. Application of Zn significantly increased Zn concentration in the leaves of bean plants. Under Zn and HI stress, the Zn-deficient and Zn-excess conditions significantly increased the EC, MDA and H₂O₂ content of excised leaves of bean. The SOD activity was found to be increased significantly in both Zn-deficiency and Zn-excess leaves under Zn and HI stress. Under both Zn and HI stress conditions, the antioxidant enzyme activities; POX, PPO and the non-enzymatic antioxidants, AsA and proline accumulation were found to be significantly increased in the Zn-excess leaves which showed that the bean plant had the ability to tolerate the excess level of Zn and HI stress. A significant increase in MDA, H₂O₂, and EC with a simultaneous decrease in the antioxidant enzyme activities under Zn-deficiency compared to Zn-sufficient condition shows the inefficiency of the bean plant in response to Zn deficiency. To the best of our knowledge, this is the first report on the effect of Zn stress combined with HI stress in bean plant.     

Oxidative stress and antioxidant responses of mulberry (Morus alba) plants subjected to deficiency and excess of manganese

The aim of the study was to relate the effects of deficiency and excess of Mn with the generation of reactive oxygen species (ROS) and altered cellular redox environment in mulberry (Morus alba L.) cv. Kanva-2 plants. Mn deficiency symptom appeared as mild interveinal chlorosis in middle leaves. Mn-excess did not produce any specific symptom. Leaf water potential (Ψ) was increased in Mn-deficient and Mn-excess mulberry plants. Mn-deficient leaves contained less Mn, less chloroplastic pigments and high tissue Fe, Zn and Cu concentrations. Starch content was increased with increasing Mn supply. While reducing sugar content increased in Mn-deficient and Mn-excess plants as well, non-reducing sugars remained unaffected in Mn-deficient plants and decreased in Mn-excess plants. Moreover, study of antioxidative responses, oxidative stress (H₂O₂ and lipid peroxidation) and cellular redox environment [dehydroascorbate (DHA)/ascorbic acid (AsA) ratio] in Mn-stressed mulberry plants was also undertaken. Both hydrogen peroxide and lipid peroxidation were enhanced in the leaves of Mn-deficient plants. Increased H₂O₂ concentration in Mn-excess leaves did not induce oxidative damage as indicated by no change in lipid peroxidation. The ratio of the redox couple (DHA/AsA) was increased both in Mn-deficient or Mn-excess plants. The activities of superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) increased in Mn-deficient plants. The activity of ascorbate peroxidase (EC 1.11.1.11) increased with increasing Mn supply. The results suggest that deficiency or excess of Mn induces oxidative stress through enhanced ROS generation and disturbed redox couple in mulberry plants.     

Impact of excess zinc on growth parameters, cell division, nutrient accumulation, photosynthetic pigments and oxidative stress of sugarcane (Saccharum spp.)

The present study employed a sand culture experiment with three levels of zinc viz., 0.065 (control), 65.0 and 130 mg l^?1 Zn (excess) as zinc sulfate, respectively, in sugarcane (Saccharum spp.), cultivar CoLk 8102. The results indicated growth depression, dark green leaves, decreased root number and length and sharp depression in mitotic activity of roots due to high doses of Zn (65 and 130 mg l^?1); effects were significant at 130 mg l^?1 Zn supply. The endogenous ion contents measurements revealed roots to be the major sink for excess Zn with lower amounts in leaves of sugarcane plants. High level of Zn decreased total phosphorus in leaves and increased it in roots. Fe and Cu content decreased, while, Mn increased in sugarcane plants due to high Zn in the growing medium. Plants experienced oxidative stress when exposed to higher levels of zinc. Biochemical investigations indicated high level of hydrogen peroxide, malondialdehyde contents with high chlorophyll a, b and carotenoids contents and activity of superoxide dismutase, catalase and peroxidase enzymes under high Zn conditions. These findings confirm suggest that excess Zn adversely affects root growth and mitotic efficiency, enhances chromosomal aberrations and increases growth and nutrient accumulation abnormalities, as well as oxidative stress.     

Zinc stress induces physiological,ultra-structural and biochemical changes in mandarin orange (Citrus reticulata Blanco) seedlings

Zinc (Zn) is an essential micronutrient for higher plants; yet, at higher concentrations it is toxic. In order to explore the effect of Zn stress on growth, biochemical, physiological and ultra-structural changes, 1 year old mandarin plants were grown under various Zn concentrations (1, 2, 3, 4, 5, 10 15 and 20 mM) for 14 weeks. The biomass of the plants increased with increasing Zn concentrations and finally declined under excess Zn concentration but the prime increase was observed at 4 and 5 mM Zn. Zn stress reduced the photosynthetic rate, stomatal conductance, and transpiration along with reduction of chlorophyll a, chlorophyll b, and carotenoids content in leaf. Superoxide anion, malondialdehyde, hydrogen peroxide and electrolyte leakage were elevated in Zn stressed plants. The activities of ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6), superoxide dismutase (EC 1.15.1.1) and peroxidase (EC 1.11.1.7) enzymes were increased in both Zn-deficient and Zn-excess plants. Therefore it is suggested that antioxidant defense system did not sufficiently protect the plants under rigorous Zn stress which was also corroborated by the alteration in cell ultrastructure as revealed by transmission electron microscopy.     

A DESD-box helicase functions in salinity stress tolerance by improving photosynthesis and antioxidant machinery in rice (Oryza sativa L. cv. PB1)

The exact mechanism of helicase-mediated salinity tolerance is not yet understood. We have isolated a DESD-box containing cDNA from Pisum sativum (Pea) and named it as PDH45. It is a unique member of DEAD-box helicase family; containing DESD instead of DEAD/H. PDH45 overexpression driven by constitutive cauliflower mosaic virus-35S promoter in rice transgenic [Oryza sativa L. cv. Pusa Basmati 1 (PB1)] plants confers salinity tolerance by improving the photosynthesis and antioxidant machinery. The Na⁺ ion concentration and oxidative stress parameters in leaves of the NaCl (0, 100 or 200 mM) treated PDH45 overexpressing T₁ transgenic lines were lower as compared to wild type (WT) rice plants under similar conditions. The 200 mM NaCl significantly reduced the leaf area, plant dry mass, net photosynthetic rate (P_N), stomatal conductance (gs), intercellular CO₂ (Ci), chlorophyll (Chl) content in WT plants as compared to the transgenics. The T₁ transgenics exhibited higher glutathione (GSH) and ascorbate (AsA) contents under salinity stress. The activities of antioxidant enzymes viz. superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and glutathione reductase (GR) were significantly higher in transgenics; suggesting the existence of an efficient antioxidant defence system to cope with salinity induced-oxidative damage. Yeast two-hybrid assay indicated that the PDH45 protein interacts with Cu/Zn SOD, adenosine-5′-phosphosulfate-kinase, cysteine proteinase and eIF(4G), thus confirming the involvement of ROS scavenging machinery in the transgenic plants to provide salt tolerance. Furthermore, the T₂ transgenics were also able to grow, flower, and set viable seeds under continuous salinity stress of 200 mM NaCl. This study provides insights into the mechanism of PDH45 mediated salinity stress tolerance by controlling the generation of stress induced reactive oxygen species (ROS) and also by protecting the photosynthetic machinery through a strengthened antioxidant system.     

Decrease in nitrate uptake and increase in proton release in zinc deficient cotton,sunflower and buckwheat plants

The effect of varied Zn supply on the pH of the nutrient solution and uptake of cations and anions was studied in cotton (Gossypium hirsutum L.), sunflower (Helianthus annuus L.) and buckwheat (Fagopyrum esculentum Moench) plants grown under controlled environmental conditions in nutrient solutions with nitrate as source of nitrogen. With the appearance of visual Zn deficiency symtoms, the pH of the nutrient solutions decreased from 6 to about 5 whereas the pH increased to about 7 when the plants were adequately supplied with Zn. In Zn deficient plants the pH decrease was associated with a shift in the cation-anion uptake ratio in favour of cation uptake. Of the major ions, uptake of Ca²⁺ and K⁺ was either not affected or only slightly lowered whereas NO₃ ^- uptake was drastically decreased in Zn deficient plants. Although the Zn nutritional status of plants hardly affected the NO₃ ^- concentrations in the plants, the leakage of NO₃ ^- from roots of Zn deficient plants into a diluted CaCl₂ solution was nearly 10 times higher than that of plants adequately supplied with Zn. In contrast to Zn deficiency, Mn deficiency in cotton plants neither affected NO₃ ^- uptake nor the pH of the nutrient solution.The results indicate that, probably as a consequence of the role of Zn in plasma membrane integrity and nitrogen metabolism, when Zn is deficient in dicotyledonous species net uptake of NO₃ ^- is particularly depressed which in turn results in an increase in cation-anion uptake ratio and a corresponding decrease in external pH. The ecological relevance of this rhizosphere acidification is discussed.     

Diurnal changes in photosynthesis and antioxidants of Angelica sinensis as influenced by cropping systems

Diurnal dynamics of photosynthetic character of Angelica sinensis, as well as effect of continuous cropping on leaf photosynthetic character, antioxidant enzyme activity and growth of A. sinensis were investigated under field condition. The results showed that the diurnal net photosynthetic rate of A. sinensis in sunny day exhibited a double-peak pattern, and the peaks occurred at 9:45 and 16:45 h, respectively. There was a significant midday depression with A. sinensis, which was caused principally by stomatal factors such as stomatal conductance. The results also showed that net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), and chlorophyll content (Chl) of A. sinensis plants under continuous cropping were significantly lower than those of the control. The activity of total superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and growth parameters of A. sinensis plants were significantly decreased under continuous cropping condition. This study provides evidence of continuous cropping obstacle effect on photosynthesis, antioxidant enzyme activity, and growth parameters of A. sinensis in a field experiment, which partly explained the yield reduction of A. sinensis in the field, when it was cultivated continuously on the same soil.     

Induction of oxidative stress and antioxidant responses in <Emphasis Type="Italic">Vigna mungo</Emphasis> by zinc stress

Significant changes were observed in the antioxidant systems in the leaves of black gram (Vigna mungo L., var. DPU-88-31) grown under deficient and excess supply of Zn. Plant grown with Zn supply ranging from 0.01 to 10.0 μM under glasshouse conditions showed optimal growth and biomass yield at 1.0 μM Zn supply. Deficient (0.001 and 0.01 μM) as well as excess (2.0 and 10.0 μM) supply of Zn decreased the concentrations of chlorophyll, carotenoids, and nonprotein thiols and increased that of ascorbate. The activity of superoxide dismutase and carbonic anhydrase was decreased at deficient levels and increased with increase in Zn supply up to 10 μM. At both stages of growth, the activities of antioxidant enzymes, such as catalase and ascorbate peroxidase, were decreased, whereas the activities of glutathione reductase and peroxidase were increased at both deficient and excess supply of Zn. An accumulation of hydrogen peroxide and thiobarbituric acid-reactive substances was observed in Zn-stressed leaves, indicating oxidative damage. Different responses to deficient and excess supply of Zn were observed in the production of oxidative damage.     

Effect of phosphorus deficiency on the photosynthetic characteristics of rice plants

The effects of phosphorus deficiency on the photosynthetic characteristics were studied in rice seedlings (Oryza sativa L.) every 8 days after treatment. P deficiency caused a significant reduction in the net photosynthesis rate (P _N) in rice plants. During the first 16 days of P deficiency, the maximum efficiency of PSII photochemistry (F _v/F _m), the effective PSII quantum yield (ϕ_PSII), the electron transport rate (ETR) as well as photochemical quenching (qP) in the P-limited rice plants kept close to the control, but the excitation energy capture efficiency of PSII reaction centers (F′_v/F′_m) was significantly declined in the P-deficient rice leaves. Meanwhile, in the stressed leaves, we also found a significant increase in nonphotochemical quenching (NPQ) as well as in the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX). It was indicated that a series of photoprotective mechanisms had been initiated in rice plants in response to short-term P deficiency. Therefore, PSII functioning was not affected significantly under such stress. As P deficiency continued, the excess excitation energy was accumulated in excess of the capacity of photoprotection systems. When the rice suffered from P deficiency more than 16 days, ϕ_PSII, ETR, and qP were decreased more rapidly than that in the control plants, although NPQ still kept higher in the stressed plants. These results were also consistent with the data on the distribution of excitation energy. The excess energy induced the generation of reactive oxygen species, which might lead to the further damage to PSII functioning. This text was submitted by the authors in English.     

Changes in photosynthesis, chlorophyll fluorescence, and antioxidant enzymes of mulberry (Morus ssp.) in response to salinity and high-temperature stress

Photosynthesis, chlorophyll (Chl) fluorescence, and antioxidant enzymes were measured in the mulberry (Morus spp.) cultivars Da 10, Hongguo 2, Anza 1, and Taiwan 72C002, which were subjected to salinity and high-temperature stress (STS; 0.1%, 0.3%, and 0.5% NaCl concentrations, 34.5°C–40.5°C/27.8°C–29.2°C day/night temperatures). Control plants were watered with 1 L of full-strength Hoagland’s nutrient solution with no added NaCl. Net photosynthetic rate (P _N), stomatal conductance (g _s), and effective quantum yield of photosystem II photochemistry (Φ_PSII) increased in Anza 1 and Taiwan 72C002 under 0.1% STS but decreased in Da 10 and Hongguo 2 compared with the control. However, all the above parameters, including Chl content, maximum quantum yield of photosystem II photochemistry (F_v/F_m), nonphotochemical quenching (NPQ), and maximum carboxylation velocity of Rubisco (V _cmax, decreased in Taiwan 72C002, Honggua 2, and Da 10 under 0.3% and 0.5% STS, suggesting that photoinhibition occurred under severe STS. Under STS, there were no significant changes in P _N, F_v/F_m, Φ_PSII, ascorbate peroxidase (APX) activity, superoxide dismutase (SOD) activity, catalase activity, superoxide anion radical (O ₂ ^? ) content, malondialdehyde (MDA) content, soluble sugar content (SSC), and leaf biomass in Anza 1 even at 0.5% STS, showing that Anza 1 displays high resistance to STS. In addition, peroxidase activity was significantly higher in Anza 1 than in the other mulberry cultivars. Significant adverse effects of severe salinity on photosynthesis and Chl fluorescence parameters were observed in Da 10. Additionally, SOD, peroxidase, and APX activities were lower in Da 10, whereas O ₂ ^? and MDA contents were higher in comparison with the other mulberry cultivars under 0.3% and 0.5% STS, suggesting that Da 10 had low resistance to STS. These results show that 0.1% STS had a positive effect on photosynthesis and Chl fluorescence parameters in Anza 1 and Taiwan 72C002, and higher peroxidase activity can to a certain extent explain the higher STS tolerance in Anza 1. Damages to DSM photosystems might be related to lower SOD, POD, and APX activities, which resulted in the accumulation of reactive oxygen species.     

Antioxidant responses and water status in Brassica seedlings subjected to boron stress

The effect of boron (B) on growth, water status and oxidative damage was investigated in the leaves and roots of 7-day-old seedlings of Brassica juncea var. Varuna. For this seedlings of Brassica were grown in solution culture with variable boron supply (0.033, 0.33, 3.3 and 33 mg B L^?1) under controlled conditions in green house. Photosynthetic pigments were found to be decreased more under excess (3.3 and 33 mg B L^–1) than deficient boron supply (0.033 mg B L^–1) when compared to control (0.33 mg B L^–1). Accumulation of hydrogen peroxide and thiobarbituric acid reactive substances content in both leaves and roots under deficient and excess boron supply suggested oxidative damage due to excessive production of reactive oxygen species. Increased activity of antioxidative enzymes: superoxide dismutase, catalase and peroxidase along with polyphenol oxidase was observed in leaves and roots under boron deficiency and excess than in control. Increased proline concentration, decreased total water content and water saturation deficit also indicated the water deficit condition in leaves and roots of boron-stressed Brassica seedlings.     

Boron excess affects photosynthesis and antioxidant apparatus of greenhouse Cucurbita pepo and Cucumis sativus

This study aimed to evaluate the behavior of zucchini (Cucurbita pepo L.) and cucumber (Cucumis sativus L.) under boron (B) excess. Plants were grown under greenhouse conditions in a sandy soil–peat mixture using a nutrient solution containing 0.2 (control), 10 and 20 mg L^?1 B. Visible symptoms were quantified and leaf B accumulation, gas exchanges, chlorophyll (Chl) a fluorescence, malondialdehyde by-products and antioxidants were investigated 20 days after the beginning of the treatments. Boron toxicity induced oxidative load and leaf necrotic burns coupled with the reduction of leaf growth and biomass accumulation in both species. Boron excess resulted in a decrease of Chl a/b ratio, potential (F_v/F_m) and actual (Φ_PSII) PSII quantum efficiency, photosynthetic rate (Pn), stomatal conductance (g_s), and transpiration (E) as well. A general stimulation of the antioxidant enzymes ascorbate peroxidase, catalase and superoxide dismutase was observed, and a significant increase in the oxidized form of ascorbate and glutathione was evidenced for treated plants of both species. A difference between the two species was observed: C. pepo appeared to be more sensitive to B stress being damaged at all B concentration. C. sativus grown at 10 mg L^?1 B in nutrient solution showed some down-regulated mechanisms, i.e. increase in Chl b content and a good photochemical PSII efficiency as well as a higher amount of constitutive antioxidant molecules, that, however, are not sufficient to contrast the negative effects of B.     

Phosphites of manganese and zinc potentiate the resistance of common bean against infection by Xanthomonas axonopodis pv. phaseoli

Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli var. fuscans (Xapf), negatively impact common bean production globally. Considering the potential of phosphites to protect plants against different diseases, this study investigated the potential of using manganese (Mn) and zinc (Zn) phosphites in common bean for CBB control. Plants were inoculated with Xapf 48 hr after being sprayed with water (control) and solutions (7.5 ml/L) of Mn and Zn phosphites. The area under common bacterial blight progress curve (AUCBBPC) was significantly lower by 34% and 59% for Mn and Zn phosphite treatments in comparison with the control treatment. The AUCBBPC was significantly reduced by 38% for Zn phosphite-sprayed plants compared to Mn phosphite treatment. Phosphite-sprayed plants displayed higher values for area under the curves of net CO₂ assimilation rate, stomatal conductance to water vapour, transpiration rate and internal-to-ambient CO₂ concentration ratio than non-sprayed plants. This indicates the effect of Mn and Zn phosphites in attenuating the photochemical dysfunctions caused by Xapf infection. Moreover, plants sprayed with Mn phosphite displayed higher values for area under the curves of efficiency in capturing the excitation energy of open reaction centres of PSII and electron transport rate than those non-sprayed indicating their capacity to preserve the capture and the use of the collected energy more efficiently. Lower AUCBBPC for Zn phosphite-sprayed plants resulted in higher concentrations of total chlorophylls. The Zn phosphite-sprayed plants showed higher values for area under the curves of β-1,3-glucanase, phenylalanine ammonia-lyase, polyphenoloxidase, ascorbate peroxidase and superoxide dismutase activities. The Zn phosphite spray primed the plants to enhance their defence response and antioxidant capacity to reduce Xapf-triggered oxidative stress with the preservation of the photosynthetic apparatus more efficiently.     

OsZIP5 is a plasma membrane zinc transporter in rice

Zinc is essential for normal plant growth and development. To understand its transport in rice, we characterized OsZIP5, which is inducible under Zn deficiency. OsZIP5 complemented the growth defect of a yeast Zn-uptake mutant, indicating that OsZIP5 is a Zn transporter. The OsZIP5-GFP fusion protein was localized to the plasma membrane. Transgenic plants overexpressing the gene grew less well. Overexpression of the gene decreased the Zn concentration in shoots, but caused it to rise in the roots. Knockout plants showed no visible phenotypic changes under either normal or deficient conditions. However, they were tolerant to excess Zn and contained less Zn. In contrast, overexpressing transgenics were sensitive to excess Zn. These results indicate that OsZIP5 plays a role in Zn distribution within rice.     

Effects of cytokinin on photosynthetic gas exchange, chlorophyll fluorescence parameters, antioxidative system and carbohydrate accumulation in cucumber (Cucumis sativus L.) under low light

The effects of 6-benzylaminopurine (6-BA) on plant growth, net photosynthetic rate, relative chlorophyll content, soluble protein, carbohydrates contents and antioxidant systems of cucumber (Cucumis sativus L.) under low-light environment were investigated using two different cucumber cultivars. The results showed that the weak light resulted in the remarkable decrease in plant net photosynthetic rate, relative chlorophyll content, soluble protein and carbohydrates contents, but promoted the superoxide dismutase and guaiacol peroxidase activities. However, application of 6-BA alleviated the reduction of the correlative parameters and mediated the changes of antioxidant systems. The potential mechanisms may involve the following aspects: 6-BA clearly enhanced the plants’ tolerance to low light by increasing chlorophyll content, reducing the production of superoxide radical (O ₂ ^·? ), and enhancing the quenching of hydrogen peroxide (H₂O₂), consequently alleviating the injury of photosynthetic system, and further increasing the efficiency of CO₂ assimilation, producing more carbohydrates which can meet the growth need of cucumber. Meanwhile, the present study indicated that cucumber of Europe mini type (Chunqiuwang) was more tolerant to low light than HuaNan type (Huza No.3).