Lanthanum improves the cadmium tolerance of <Emphasis Type="Italic">Zea mays</Emphasis> seedlings by the regulation of ascorbate and glutathione metabolism

The effect of lanthanum on the metabolism of ascorbate (AsA) and glutathione (GSH) in the leaves of maize seedlings under cadmium stress was investigated. The findings showed that Cd remarkably increased electrolyte leakage (EL), the activities of ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase (MDHAR), glutathione reductase, L-galactono-1,4-lactone dehydrogenase, and γ-glutamylcysteine synthetase, and the content of reduced AsA, reduced GSH, total AsA, total GSH, malondialdehyde (MDA), and Cd, compared with control. However, Cd significantly decreased the dry biomass of roots and shoots. Treatment with La + Cd evidently increased the activities of above enzymes except MDHAR, the content of reduced AsA, reduced GSH, total AsA and total GSH, and the dry biomass of roots and shoots, compared with Cd stress alone. Meanwhile, treatment with La + Cd remarkably decreased EL and the content of Cd and MDA compared with Cd stress alone. Our results suggested that La could be used as a regulator to improve the Cd tolerance of maize for its role in the alleviation of Cd-induced oxidative damage by regulating the metabolism of AsA and GSH.     

Cadmium effects on mineral nutrition and stress in <Emphasis Type="Italic">Potamogeton crispus</Emphasis>

The mechanisms of plant tolerance to cadmium stress were studied by short-term exposure of Potamogeton crispus L. to various concentrations of Cd ranging from 0 to 0.09 mM. The accumulation of Cd and its influence on nutrient elements, chlorophyll pigments, ultrastructure, proline and MDA contents, and free radical production, as well as the activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR) were investigated. The higher Cd concentration in the medium resulted in a significant enhancement of Cd accumulation. Photosynthetic pigment content decreased and ultrastructural damage to the leaf cells was aggravated with the increase in the Cd concentrations. Disruption of chloroplasts and mitochondria was observed even at the lowest concentration of Cd. Meantime, the rate of O₂^*− generation and the contents of H₂O₂ and MDA significantly increased under Cd stress, suggesting that Cd caused oxidative stress. In addition, the antioxidant system was clearly activated following Cd exposure. SOD and POD activities increased initially and then decreased, while APX and GR activities markedly increased. Simultaneously, mineral nutrition was disturbed. While K, P, Ca, and Cu contents decreased, Na, Fe, and Mn contents increased. Induction of antioxidant enzyme activities in leaves exposed to elevated Cd concentrations may be involved in Cd tolerance of P. crispus.     

外源一氧化氮对镉胁迫下绿豆幼苗根尖抗氧化酶的影响

采用水培法研究外源一氧化氮对镉(Cd)胁迫下绿豆幼苗根尖抗氧化酶活性的影响。结果表明:0.01mmol/L和0.1mmol/L一氧化氮供体硝普钠(sodium nitroprusside,SNP)显著促进上胚轴生长,1mmol/LSNP则抑制绿豆幼苗生长。Cd单独处理抑制根尖抗坏血酸过氧化物酶(ascorbate peroxidase,APX)和超氧化物歧化酶(superoxide dismutase,SOD)活性而刺激脂氧合酶(lipoxygenase,LOX)、谷胱甘肽转硫酶(glutathione S-transferase,GST)、谷胱甘肽还原酶(glutathione reductase,GR)和过氧化物酶(guaiacol peroxidase,POD)活性上升。0.1mmol/LSNP预处理能够明显缓解Cd对根生长的抑制,降低根尖中MDA含量,提高根尖APX和SOD活性,降低LOX和POD活性,但不影响GST和GR活性。     

Nitric oxide acts as a signal molecule in microwave pretreatment induced cadmium tolerance in wheat seedlings

The microwave has been widely used in the field of biology with the development of microwave technology. Previous studies suggest that suitable doses of microwave irradiation improved plant metabolism and enzymatic activities under cadmium stress and enhanced cadmium tolerance in wheat seedlings. The objective of this study was to test whether nitric oxide is involved in microwave pretreatment induced cadmium tolerance in wheat seedlings due to its nature as a second messenger in stress responses. Plant were treated with 10 s microwave pretreatment, microwave pretreatment in combination with NO scavenger, 2-(4-carboxyphenyl)-4, 4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) and their effects on the lipid peroxidation, the activities of antioxidant enzymes, the concentration of antioxidant compounds and wheat seedlings growth and development were compared. The results showed that 10 s microwave pretreatment dramatically alleviated growth suppression induced by cadmium stress, reflected by decreased malondialdehyde, hydrogen peroxide and superoxide radical production. Furthermore, the activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase and glutathione reductase) and the concentration of antioxidant metabolites (ascorbate, reduced glutathione, carotenoids and nitric oxide) were increased in wheat seedlings pretreated with microwave under cadmium stress. Nevertheless, the promotive effect of microwave pretreatment induced cadmium tolerance in wheat seedlings was effectively reversed by the addition of 0.5 % (w/v) cPTIO (NO scavenger), suggesting that NO was involved in microwave pretreatment induced cadmium tolerance in wheat seedlings.     

N-acetyl-cysteine alleviates Cd toxicity and reduces Cd uptake in the two barley genotypes differing in Cd tolerance

A hydroponic experiment was carried out to study the physiological mechanisms of N-acetyl cysteine (NAC) in mitigating cadmium (Cd) toxicity in two barley (Hordeum vulgare L.) genotypes, Dong 17 (Cd-sensitive) and Weisuobuzhi (Cd-tolerant). Addition of 200 μM NAC to a culture medium containing 5 μM Cd (Cd + NAC) markedly alleviated Cd-induced growth inhibition and toxicity, maintained root cell viability, and dramatically depressed O ₂ ^·? and ·OH, and malondialdehyde accumulation, significantly reduced Cd concentration in leaves and roots, especially in the sensitive genotype Dong 17. External NAC counteracted Cd-induced alterations of certain antioxidant enzymes, e.g., brought root superoxide dismutase and glutathione reductase, leaf/root peroxidase and glutathione peroxidase activities of the both genotypes down towards the control level, but elevated Cd-stress-depressed leaf catalase in Dong 17 and root ascorbate peroxidase activities in both genotypes. NAC counteracted Cd-induced alterations in amino acids and microelement contents. Furthermore, NAC significantly reduced Cd-induced damage to leaf/root ultrastructure, e.g. the shape of chloroplasts in plants treated with Cd + NAC was relatively normal with well-structured thylakoid membranes and parallel pattern of lamellae but less osmiophilic plastoglobuli compared with Cd alone treatment; nuclei of root cells were better formed and chromatin distributed more uniformly in both genotypes. These results suggested that under Cd stress, NAC may protects barley seedlings against Cd-induced damage by directly and indirectly scavenging reactive oxygen species and by maintaining stability and integrity of the subcellular structure.     

Cadmium-induced oxidative damage in mustard [Brassica juncea (L.) Czern. & Coss.] plants can be alleviated by salicylic acid

The present study was carried out to examine the effects of salicylic acid (SA) on growth, activities of antioxidant enzymes and some physio-biochemical attributes in mustard [Brassica juncea (L.) Czern. & Coss.] plants exposed to cadmium (Cd) stress. Increasing concentrations of Cd led to decreased growth, shoot biomass, relative water content (RWC) and rate of photosynthesis (A). SA allayed the adverse effects of Cd on growth, RWC, and A, but the inhibitory effect of Cd on stomatal conductance (g_s) and transpiration rate (E) was further promoted due to SA treatment. Cadmium-induced oxidative stress increased proline, lipid peroxidation and electrolyte leakage, but on exposure to SA, these parameters showed a marked decrease. Lower concentrations of Cd caused enhanced Cd transport into the plant. Cadmium suppressed the uptake of macro- and micro-nutrients, but exogenous application of SA restored the capability of plants to accumulate essential elements. SA mitigated the Cd-induced inhibition in the growth of mustard plants. Cadmium-induced increase in the activities of some key antioxidant enzymes, superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR) was reduced by the exogenous application of SA. This reflects that SA might have acted as one of the potential antioxidants in mustard plants under Cd stress.     

Selenium alleviates cadmium toxicity by preventing oxidative stress in sunflower (Helianthus annuus) seedlings

The present study investigated the possible mediatory role of selenium (Se) in protecting plants from cadmium (Cd) toxicity. The exposure of sunflower seedlings to 20 μM Cd inhibited biomass production, decreased chlorophyll and carotenoid concentrations and strongly increased accumulation of Cd in both roots and shoots. Similarly, Cd enhanced hydrogen peroxides content and lipid peroxidation as indicated by malondialdehyde accumulation. Pre-soaking seeds with Se (5, 10 and 20 μM) alleviated the negative effect of Cd on growth and led to a decrease in oxidative injuries caused by Cd. Furthermore, Se enhanced the activities of catalase, ascorbate peroxidase and glutathione reductase, but lowered that of superoxide dismutase and guaiacol peroxidase. As important antioxidants, ascorbate and glutathione contents in sunflower leaves exposed to Cd were significantly decreased by Se treatment. The data suggest that the beneficial effect of Se during an earlier growth period could be related to avoidance of cumulative damage upon exposure to Cd, thus reducing the negative consequences of oxidative stress caused by heavy metal toxicity.     

Cadmium-induced changes in antioxidative systems,hydrogen peroxide content,and lipid peroxidation in<Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

To study the relationship between cadmium (Cd)-induced phytotoxicity and oxidative stress, we grew Cd-sensitive wild-type (WT) and Cd-resistant type (RT) seedlings ofArabidopsis thaliana on MS media containing up to 500 μM CdCl₂. The resistant seedlings showed higher biomasses and lower hydrogen peroxide and lipid peroxidation levels, the latter expressed in terms of malondialdehyde (MDA) production. These results indicate that RT plants experience lower oxidative stress when exposed to Cd. Furthermore, compared with the WT, RT seedlings have significantly higher activities of superoxide dismutase (SOD) and enzymes related to hydrogen peroxide removal, e.g., guaiacol peroxidase (GPX), ascorbate peroxidase (APX), and glutathione reductase (GR). These differential responses suggest that such phytotoxicity could be induced by oxidative stress, and that lower accumulations of hydrogen peroxide confer Cd tolerance in seedlings.     

Differential responses to cadmium induced oxidative stress in marine macroalga Ulva lactuca (Ulvales, Chlorophyta)

This study describes various biochemical processes involved in the mitigation of cadmium toxicity in green alga Ulva lactuca. The plants when exposed to 0.4 mM CdCl₂ for 4 days showed twofold increase in lipoperoxides and H₂O₂ content that collectively decreased the growth and photosynthetic pigments by almost 30% over the control. The activities of antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione peroxidase (GPX) enhanced by twofold to threefold and that of catalase (CAT) diminished. Further, the isoforms of these enzymes, namely, Mn-SOD (~85 kDa), GR (~180 kDa) and GPX (~50 kDa) responded specifically to Cd²⁺ exposure. Moreover, the contents of reduced glutathione (3.01 fold) and ascorbate (1.85 fold) also increased substantially. Lipoxygenase (LOX) activity increased by two fold coupled with the induction of two new isoforms upon Cd²⁺ exposure. Among the polyunsaturated fatty acids, although n ? 3 PUFAs and n ? 6 PUFAs (18:3n ? 6 and C18:2n ? 6) showed relatively higher contents than control, the latter ones showed threefold increase indicating their prominence in controlling the cadmium stress. Both free and bound soluble putrescine increased noticeably without any change in spermidine. In contrast, spermine content reduced to half over control. Among the macronutrients analysed in exposed thalli, the decreased K content was accompanied by higher Na and Mn with no appreciable change in Ca, Mg, Fe and Zn. Induction of antioxidant enzymes and LOX isoforms together with storage of putrescine and n ? 6 PUFAs in cadmium exposed thallus in the present study reveal their potential role in Cd²⁺ induced oxidative stress in U. lactuca.     

Phytochelatin synthesis and response of antioxidants during cadmium stress in Bacopa monnieri L.

The phytotoxicity imposed by cadmium (Cd) and its detoxifying responses of Bacopa monnieri L. have been investigated. Effect on biomass, photosynthetic pigments and protein level were evaluated as gross effect, while lipid peroxidation and electrolyte leakage reflected oxidative stress. Induction of phytochelatins and enzymatic and non-enzymatic antioxidants were monitored as plants primary and secondary metal detoxifying responses, respectively. Plants accumulated substantial amount of Cd in different plant parts (root, stem and leaf), the maximum being in roots (9240.11 microg g(-1) dw after 7 d at 100 microM). Cadmium induced oxidative stress, which was indicated by increase in lipid peroxidation and electrical conductivity with increase in metal concentration and exposure duration. Photosynthetic pigments showed progressive decline while protein showed slight increase at lower concentrations. Enzymes viz., superoxide dismutase (SOD, EC 1.15.1.1), guaiacol peroxidase (GPX, EC 1.11.1.7) ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) showed stimulation except catalase (CAT, EC 1.11.1.6) which showed declining trend. Initially, an enhanced level of cysteine, glutathione and non-protein thiols was observed, which depleted with increase in exposure concentration and duration. Phytochelatins induced significantly at 10 microM Cd in roots and at 50 microM Cd in leaves. The phytochelatins decreased in roots at 50 microM Cd, which may be correlated with reduced level of GSH, probably due to reduced GR activity, which exerted increased oxidative stress as also evident by the phenotypic changes in the plant like browning of roots and slight yellowing of leaves. Thus, besides synthesis of phytochelatins, availability of GSH and concerted activity of GR seem to play a central role for Bacopa plants to combat oxidative stress caused by metal and to detoxify it. Plants ability to accumulate and tolerate high amount of Cd through enhanced level of PCs and various antioxidants suggest it to be a suitable candidate for phytoremediation.     

Exogenous Selenium Pretreatment Protects Rapeseed Seedlings from Cadmium-Induced Oxidative Stress by Upregulating Antioxidant Defense and Methylglyoxal Detoxification Systems

The protective effect of selenium (Se) on antioxidant defense and methylglyoxal (MG) detoxification systems was investigated in leaves of rapeseed (Brassica napus cv. BINA sharisha 3) seedlings under cadmium (Cd)-induced oxidative stress. Two sets of 11-day-old seedlings were pretreated with both 50 and 100???M Se (Na₂SeO₄, sodium selenate) for 24?h. Two concentrations of CdCl₂ (0.5 and 1.0?mM) were imposed separately or on the Se-pretreated seedlings, which were grown for another 48?h. Cadmium stress at any levels resulted in the substantial increase in malondialdehyde and H₂O₂ levels. The ascorbate (AsA) content of the seedlings decreased significantly upon exposure to Cd stress. The amount of reduced glutathione (GSH) increased only at 0.5?mM CdCl₂, while glutathione disulfide (GSSG) increased at any level of Cd, with concomitant decrease in GSH/GSSG ratio. The activities of ascorbate peroxidase (APX) and glutathione S-transferase (GST) increased significantly with increased concentration of Cd (both at 0.5 and 1.0?mM CdCl₂), while the activities of glutathione reductase (GR) and glutathione peroxidase (GPX) increased only at moderate stress (0.5?mM CdCl₂) and then decreased at 1.0?mM severe stress (1.0?mM CdCl₂). Monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT), glyoxalase I (Gly I), and glyoxalase II (Gly II) activities decreased upon exposure to any levels of Cd. Selenium pretreatment had little effect on the nonenzymatic and enzymatic components of seedlings grown under normal conditions; i.e., they slightly increased the GSH content and the activities of APX, GR, GST, and GPX. On the other hand, Se pretreatment of seedlings under Cd-induced stress showed a synergistic effect; it increased the AsA and GSH contents, the GSH/GSSG ratio, and the activities of APX, MDHAR, DHAR, GR, GPX, CAT, Gly I, and Gly II which ultimately reduced the MDA and H₂O₂ levels. However, in most cases, pretreatment with 50???M Se showed better results compared to pretreatment with 100???M Se. The results indicate that the exogenous application of Se at low concentrations increases the tolerance of plants to Cd-induced oxidative damage by enhancing their antioxidant defense and MG detoxification systems.     

Effect of exogenous nitric oxide on sulfur and nitrate assimilation pathway enzymes in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) under drought stress

The present study aimed at investigating the effects of foliar applied nitric oxide (as SNP [sodium nitroprusside]) on sulfur (glutathione reductase, guaiacol peroxidase, and glutathione S-transferase) and nitrate assimilation (nitrite and nitrate reductase) pathway enzymes in maize (Zea mays L.) exposed to water deficit conditions. The seedlings of a drought tolerant (NK8711) and sensitive (P1574) maize hybrid were applied with various SNP doses (0, 50, 100, 150, and 200 µM) under normal and drought stress conditions. Foliar spray of 100 µM markedly improved water status and chlorophyll contents and alleviated drought-induced oxidative damages through increased antioxidant (catalase, ascorbate peroxidase, and superoxide dismutase) activities in both maize hybrids. Moreover, exogenous SNP supply increased nitrite and nitrate reductase activities and upregulated glutathione reductase, glutathione S-transferase, and guaiacol peroxidase compared to no SNP supply. Interestingly, the negative effects of excess NO generation at high SNP doses (150, 200 µM) were more pronounced in P1574 than NK8711 leading to lower biomass accumulation in drought-sensitive hybrid.     

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.     

Effects of Cadmium,Chromium and Lead on Growth,Metal Uptake and Antioxidative Capacity in <Emphasis Type="Italic">Typha angustifolia</Emphasis>

This study investigates the modulation of antioxidant defence system of Typha angustifolia after 30 days exposure of 1 mM chromium (Cr), cadmium (Cd), or lead (Pb). T. angustifolia showed high tolerance to heavy metal toxicity with no visual toxic symptom when exposed to metal stress, and Cd/Pb addition also increased plant height and biomass especially in Pb treatment. Along with increased Cr, Cd, and Pb uptake in metal treatments, there was enhanced uptake of plant nutrients including Ca and Fe, and Zn in Pb treatment. A significant increase in malondialdehyde (MDA) content and superoxide dismutase (SOD) and peroxidase (POD) activities were recorded in plants subjected to Cr, Cd, or Pb stress. Furthermore, Pb stress also improved catalase (CAT), ascorbate peroxidase (APX), and glutathione peroxidase (GPX) activities; whereas Cr stress depressed APX and GPX. The results indicate that enzymatic antioxidants and Ca/Fe uptake were important for heavy metal detoxification in T. angustifolia, stimulated antioxidative enzymes, and Ca, Fe, and Zn uptake could partially explain its hyper-Pb tolerance.     

Oxidative metabolism and protoplast culture

Summary Barley leaf blade protoplasts accumulate malonaldehyde, a product of lipid peroxidation, during culture. In addition, glutathione levels fall after protoplast isolation and the proportion of glutathione in the oxidized state rises. These data indicate oxidative stress after protoplast isolation and during culture. The cause of this phenomenon is revealed by data showing that the activities of enzymes associated with antioxidative processes including glutathione reductase and ascorbate peroxidase decrease after barley protoplast isolation. In contrast, protoplasts isolated from suspension cultured cells of bromegrass and soybean exhibit little evidence for oxidative stress and increased activities of glutathione reductase and ascorbate peroxidase. We suggest that an antioxidative response is associated with mitosis and colony formation from protoplasts, as exhibited by bromegrass and soybean. Conversely, failure of an antioxidative response is associated with low viability and absence of mitosis, as in barley. Increased viability of barley leaf protoplasts cultured on feeder layer cells is correlated with increased glutathione content and higher glutathione reductase activity.     

Ultraviolet-B- and ozone-induced biochemical changes in antioxidant enzymes of Arabidopsis thaliana.

Earlier studies with Arabidopsis thaliana exposed to ultraviolet B (UV-B) and ozone (O3) have indicated the differential responses of superoxide dismutase and glutathione reductase. In this study, we have investigated whether A. thaliana genotype Landsberg erecta and its flavonoid-deficient mutant transparent testa (tt5) is capable of metabolizing UV-B- and O3-induced activated oxygen species by invoking similar antioxidant enzymes. UV-B exposure preferentially enhanced guaiacol-peroxidases, ascorbate peroxidase, and peroxidases specific to coniferyl alcohol and modified the substrate affinity of ascorbate peroxidase. O3 exposure enhanced superoxide dismutase, peroxidases, glutathione reductase, and ascorbate peroxidase to a similar degree and modified the substrate affinity of both glutathione reductase and ascorbate peroxidase. Both UV-B and O3 exposure enhanced similar Cu,Zn-superoxide dismutase isoforms. New isoforms of peroxidases and ascorbate peroxidase were synthesized in tt5 plants irradiated with UV-B. UV-B radiation, in contrast to O3, enhanced the activated oxygen species by increasing membrane-localized NADPH-oxidase activity and decreasing catalase activities. These results collectively suggest that (a) UV-B exposure preferentially induces peroxidase-related enzymes, whereas O3 exposure invokes the enzymes of superoxide dismutase/ascorbate-glutathione cycle, and (b) in contrast to O3, UV-B exposure generated activated oxygen species by increasing NADPH-oxidase activity.     

Effects of Cadmium on Enzymatic and Non-Enzymatic Antioxidative Defences of Rice (Oryza Sativa L.)

The effects of 60-d cadmium (Cd) exposure on enzymatic and non-enzymatic antioxidative system of Oryza sativa L. seedlings at tillering stage were studied using soil culture experiment. Research findings showed that chlorophyll content of Oryza sativa L. declined with the increase in soil metal concentration. Cd pollution induced the antioxidant stress by inducing O₂ ^?1 and H₂O₂, which increased in plants; at the same time, MDA as the final product of peroxidation of membrane lipids, accumulated in plant. The antioxidant enzyme system was initiated under the Cd exposure, i.e. almost all the activities of superoxide dismutase (SOD), peroxidase, catalase, glutathione peroxidase, and ascorbate peroxidase were elevated both in leaves and roots. The non-protein thiols including phytochelatins and glutathione to scavenge toxic free radicals caused by Cd stress was also studied. The contents of phytochelatins and glutathione were about 3.12–6.65-fold and 3.27–10.73-fold in leaves, against control; and the corresponding values were about 3.53–9.37-fold and 1.41–5.11-fold in roots, accordingly.     

Effect of nitrogen deficiency on antioxidant status and Cd toxicity in rice seedlings

Effect of nitrogen (N) deficiency on antioxidant status and Cd toxicity in rice seedlings was investigated. N deficiency resulted in a reduction of shoot growth but not root growth. The contents of N-containing compounds such as nitrate, chlorophyll, and protein decreased in leaves of rice seedlings grown under N deficiency. Accumulation of abscisic acid and H₂O₂ in leaves was induced by N deficiency. The content of ascorbate and the activities of ascorbate peroxidase, glutathione reductase, and catalase in N-deficient leaves were lower than their respective control leaves. However, glutathione content was not affected and superoxide dismutase activity was increased by N deficiency. Cd toxicity in N-deficient seedlings was more pronounced than that in N-sufficient ones. Pretreatment with ascorbate or L-galactono-1,4-lactone, a biosynthetic precursor of ascorbate resulted in a reduction of Cd toxicity enhanced by N deficiency. N deficiency also resulted in an enhancement of Cd uptake in rice seedlings. The possible mechanism of Cd toxicity enhanced by N deficiency is discussed.     

黄土高原冰草叶片抗坏血酸和谷胱甘肽合成及循环代谢对干旱胁迫的生理响应

通过盆栽实验, 对干旱胁迫下黄土高原地区冰草(Agropyron cristatum)叶片的抗坏血酸和谷胱甘肽合成及循环代谢相关酶及物质含量进行了研究。结果表明: 冰草可以通过增强叶片的抗坏血酸和谷胱甘肽合成及循环代谢酶: 抗坏血酸过氧化物酶、谷胱甘肽还原酶、脱氢抗坏血酸还原酶、单脱氢抗坏血酸还原酶、L-半乳糖酸-1, 4-内酯脱氢酶和γ-谷氨酰半胱氨酸合成酶活性, 维持植物体内抗坏血酸和谷胱甘肽水平及氧化还原状态, 从而抵御干旱造成的氧化胁迫。但叶片抗坏血酸和谷胱甘肽合成及循环代谢对不同水平干旱胁迫的响应, 随胁迫时间的延长而不同。在胁迫24天以前, 严重干旱下叶片的抗坏血酸和谷胱甘肽合成及循环代谢增强较显著; 在胁迫24天后, 由于该胁迫下植物所遭受的氧化胁迫较为严重, 叶片中上述6种酶的活性均呈降低趋势。而在中度干旱下叶片抗坏血酸和谷胱甘肽合成及循环代谢相关的6种酶在整个胁迫过程中均保持较高的活性。这说明, 冰草能够长时间有效地抵御中度干旱所造成的氧化胁迫, 但只能在一定时间范围内有效地抵御严重干旱所造成的氧化胁迫, 胁迫时间延长则会降低其抵御严重干旱的能力。