Phytotoxic effects of Sicyos deppei (Cucurbitaceae) in germinating tomato seeds

The phytotoxic effect of allelochemicals is referred to as allelochemical stress and it is considered a biotic stress. Sicyos deppei G. Don (Cucurbitaceae) is an allelopathic weed that causes phytotoxicity in Lycopersicon esculentum , delaying seed germination and severely inhibiting radicle growth. This paper reports in in vitro conditions, the effects of the aqueous leachate of S. deppei —throughout tomato germination times—on (1) the dynamics of starch and sugars metabolism, (2) activity and expression of the cell wall enzymes involved in endosperm weakening that allows the protrusion of the radicle, and (3) whether abscisic acid (ABA) is involved in this altered metabolic processes. Results showed that S. deppei leachate on tomato seed germination mainly caused: (1) delay in starch degradation as well as in sucrose hydrolysis; (2) lower activity of sucrose phosphate synthase, cell wall invertase, and α-amylase; being sucrose phosphate synthase (SPS) gene expression down-regulated, and the last two up regulated; (3) also, lower activity of endo β-mannanase, β-1,3 glucanase, α-galactosidase, and exo-polygalacturonase with altered gene expression; and (4) higher content of ABA during all times of germination. The phytotoxic effect of S. deppei aqueous leachate is because of the sum of many metabolic processes affected during tomato seed germination that finally is evidenced by a strong inhibition of radicle growth.     

Role of sugarcane straw allelochemicals in the growth suppression of arrowleaf sida

Previous studies suggested that allelochemicals from sugarcane straw may suppress the growth of arrowleaf sida (Sida rhombifolia L.). A study was conducted to establish: (1) the direct or indirect role of the organic molecules from sugarcane straw leachate on the growth suppression of arrowleaf sida and (2) if leachate phytotoxins induce proline accumulation in arrowleaf sida tissues as an adaptative response to a water or an oxidative stress. Inhibition of root elongation was the primary effect of sugarcane straw leachate on arrowleaf sida grown in unsterile soil. Addition of activated charcoal to unsterile soil before incorporation of straw leachate reduced the inhibition in root growth suggesting a direct participation of organic molecules in leachate phytotoxicity on arrowleaf sida. Inorganic straw constituents did not inhibit root growth while microbial activity increased leachate phytotoxicity. Soil chemical analysis suggested a direct action of organic molecules in leachate phytotoxicity rather than variations in macro and micronutrients or nutrient microbial immobilization. Straw leachate induced proline accumulation in roots and cotyledons of arrowleaf sida. Proline increase was related with oxidative stress in the roots but not in the cotyledons. Our results indicate a direct action of organic compounds from sugarcane straw and/or their microbial transformation products on root growth of arrowleaf sida. These substances induced proline accumulation in roots mainly as consequence of an oxidative stress while water stress may be the main cause of high proline content in the cotyledons. Although the observed responses could be due to phenolic compounds, the involvement of organic molecules with other chemical nature could not be excluded.     

Allelochemical stress produced by the aqueous leachate of Callicarpa acuminata: effects on roots of bean,maize, and tomato

The in vitro effects of an aqueous leachate (1%) of Callicarpa acuminata Kunth. (Verbenaceae) on radicle growth, protein expression, catalase activity, free radical production and membrane lipid peroxidation in roots of bean, maize, and tomato were examined. Aqueous extract of C. acuminata inhibited the radicle growth of tomato by 47%, but had no effect on root growth of maize and beans. 2D-PAGE and densitometry analysis showed that C. acuminata aqueous leachate modified the expression of various proteins in the roots of all treated plants. In treated bean roots, microsequencing analysis of an 11.3-kDa protein, whose expression was enhanced by leachate treatment, revealed a 99% similarity with subunits of α -amylase inhibitor of other beans. A 27.5-kDa protein induced in treated tomato showed 69–95% similarity to glutathione- S -transferases (GST) of other Solanaceae. Spectrophotometric analysis and native gels revealed that catalase activity was increased by 2.2-fold in tomato roots and 1.4-fold in bean roots. No significant changes were observed in treated maize roots. Luminol chemiluminescence levels, a measure of free radicals, increased 3.8-fold in treated tomato roots and 2.1-fold in treated bean roots. Oxidative membrane damage in treated roots was measured by lipid peroxidation rates. In tomato we observed a 2.4-fold increase in peroxidation, however, no effect was observed in maize or beans.     

Hydroxamic acids in Secale cereale L. and the relationship with their antifeedant and allelopathic properties

Contents of the hydroxamic acids 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) in leaves and roots of 14 cultivars of rye, Secale cereale L., were determined. Dynamics of accumulation in three cultivars were evaluated. DIBOA was the main cyclic hydroxamic acid in leaves but the contents differed significantly between the cultivars. Both DIBOA and DIMBOA were present in the roots. Maximum concentration of DIBOA in leaves and DIMBOA in roots was reached between 48-54 h and 54-72 h after germination, respectively. Antifeedant activity of DIBOA towards the aphid Rhopalosiphum padi and the feeding behavior were studied by electronic recording in barley leaves treated with different contents of DIBOA. The deleterious activity of DIBOA could arise by starvation and/or a toxic effect. Additionally, allelopathic potential of pure DIBOA and aqueous extracts of leaves and roots of rye (Tetra-Baer) on the germination of lettuce (Lactuca sativa) and rye (Tetra-Baer) seeds was evaluated. A high percentage of germination inhibition of pure DIBOA and the extracts of leaves and roots was observed. The activity is in agreement with the contents of hydroxamic acids in the plants. The substrates had no allelopathic effect on rye seeds.     

化感胁迫诱导植物细胞损伤研究进展

化感胁迫(allelochemical stress)是指一种植物通过淋溶、挥发、根系分泌和残株腐解等途径释放化学物质,对另一种植物(包括微生物)产生直接或间接的伤害作用。有害化感物质对受体植物具有显著的细胞毒性,影响根边缘细胞的形成过程和活性,改变细胞壁和细胞膜的特性,破坏细胞内部结构,干扰细胞有丝分裂过程和基因表达模式;此外,化感胁迫往往伴随着氧化胁迫,受体植物细胞活性氧(ROS)水平升高,膜脂过氧化程度加剧,抗氧化系统被破坏,ROS影响与凋亡相关的信号调控过程,引起细胞大量死亡。因此,化感胁迫诱导的氧化胁迫可能是引起细胞凋亡的原因之一。阐明化感胁迫介导的氧化损伤和细胞损伤的相互关系以及根边缘细胞对化感胁迫的响应机制,是今后研究化感作用机制的一个方向。     

Basis of coffee seed sensitivity to liquid nitrogen exposure: oxidative stress or imbibitional damage?

Two hypotheses, namely the occurrence of post‐thaw oxidative stress or imbibitional damage, were tested to explain the high sensitivity of coffee seeds to liquid nitrogen (LN) exposure. Oxidative stress was studied by measuring primary and secondary products of lipid peroxidation in seeds during the desiccation and rehydration periods. The 4‐hydroxynonenal (4‐HNE) content of seeds remained constant throughout the desiccation step. No significant difference was observed between desiccated seeds and seeds desiccated and exposed to LN for the evolution of their 4‐HNE and hydroperoxide contents during rehydration. In both cases, an increase in 4‐HNE and hydroperoxide contents of seeds was observed during the first hours of culture under germination conditions, followed by a progressive decrease down to values comparable to those observed in desiccated seeds. The hydroperoxide composition of frozen seeds was not significantly different from that of control seeds. The (S)/(R) enantiomeric ratios of 9‐ and 13‐hydroxy‐octadecadienoic acid extracted from rehydrating seeds were chiral, suggesting that they originated from lipoxygenase activity. These results suggest that the high sensitivity of coffee seeds to LN exposure is not directly associated with the occurrence of an oxidative stress during post‐thaw rehydration. The effect on seed viability of different rehydration procedures previously identified to reduce membrane imbibitional injury was studied after desiccation and LN exposure. Desiccation tolerance increased with, by increasing order, seed osmoconditioning, pre‐heating and pre‐humidifying prior to their culture under germination conditions. Among the four combinations of pre‐humidification durations (24 or 48 h) and temperatures (25 or 37°C) tested, pre‐humidification for 24 h at 37°C gave the highest level of desiccation tolerance. This rehydration procedure also dramatically increased seed viability after LN exposure. Seed desiccation sensitivity modelling in combination with the calculation of the decrease in seed water activity during cooling facilitated the explanation of the beneficial effect of controlled rehydration after desiccation and LN exposure. These results support the hypothesis that imbibitional membrane damage is involved in the sensitivity of coffee seeds to LN exposure.     

Allelochemical Stress Can Trigger Oxidative Damage in Receptor Plants: Mode of Action of Phytotoxicity

Plants can interact with other plants through the release of chemical compounds or allelochemicals. These compounds released by donor plants influence germination, growth, development, and establishment of receptor plants; having an important role on the pattern of vegetation, i.e as invasive strategy, and on crop productivity. This phytotoxic or negative effect of the released allelochemicals (allelochemical stress) is caused by modifying or altering diverse metabolic processes, having many molecular targets in the receptor plants. Recently, using an aggressive and allelopathic plant Sicyos deppei as the donor plant, and Lycopersicon esculentum as the receptor plant, we showed that the allelochemicals released by S. deppei caused oxidative damage through an increase in reactive oxygen species (ROS) and activation or modification of antioxidant enzymes. Based on this study, we proposed that oxidative stress is one of the mechanisms, among others, by which an allelopathic plant causes phytotoxicity to other plants.Key Words: allelochemical stress, Sicyos deppei, Lycopersicon esculentum, plant allelochemicals, phytotoxicity, ROS, lipid peroxidationIt is well known that plants interact with many organisms, including co-habitation with other plants. Among these relations are the ones referred to as allelochemical interactions. Allelopathy can be defined as a mechanism of interference in plant growth and development mediated by the addition of plant-produced secondary products (allelochemicals) to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization, and root exudation.^1–3 These released allelochemicals become stressful only when they are toxic or when they affect the growth and development of surrounding plants (phytotoxicity). Studies on allelochemical stress have been expanding; recently the phenomenon has taken on increased importance, since it can help explain plant growth inhibition in interspecies interactions and in structuring the plant community. It appears to be one mechanism or strategy used by invasive plants to become successful and replace other native ones.^4–6On the other hand, the chemical diversity of the organic compounds that mediate these allelochemical interactions is as diverse as their modes of action. Many studies have shown that allelochemicals interfere with several physiological processes in the receptor organism.^3,7,8 The physiological effects on receptor plants or other organisms are useful in determining the role of the allelochemicals in the system. Recently, it has been proposed that allelochemicals can cause oxidative stress in target plants and therefore activate the antioxidant mechanism.^3,8–12 In particular; our studies have been focused on knowing the physiological targets of the phytotoxic compounds released by a noxious and endemic weed Sicyos deppei G. Don (Cucurbitaceae). We have taken as the model the receptor or damaged plant Lycopersicon esculentum Mill (Solanaceae), since in Mexican crop-fields, it is common to find both plants. We have observed the strong allelopathic potential of S. deppei and are exploring the potential metabolic target that could be involved in the strong phytotoxic effect of this weed.^13–16 We recently documented the oxidative damage that an aqueous leachate of S. deppei caused in the target plant L. esculentum.¹⁶ In this work we explored in seeds and in primary roots the antioxidant mechanism of tomato to determine whether or not the inhibitory effect of S. deppei was due to oxidative damage. We analyzed the activity and expression of some antioxidant enzymes involved in the detoxification of ROS, and found an imbalance in its activity as well as an increase in the levels of H₂O₂ at 24 h of treatment. Additional studies on the levels of ROS, including hydrogen peroxide, were monitored in primary roots from germinating seeds under allelochemical stress by imaging the ROS-sensitive fluorescent dye dichlorofluorescein (_H2DCFDA, carboxy-2′, 7′-diclhlorofluorescein diacetate) in a confocal microscope (BIORAD 1024, 488 nm dichroic and 510–560 nm emission). DCFDA fluorescence increases as the dye is oxidized by ROS to dichlorofluorescein (DCF). Figure 1 shows a marked increase in fluorescence at 48 h and 72 h of treatment (Fig. 1A–C) compared with the same treatment at 24 h, and with the corresponding control. This fluorescence was more evident at the root cap and at the zone of root hairs in treated seeds.Open in a separate windowFigure 1Allelochemical stress caused by S. deppei elicits ROS generation in tomato germinating seeds. Panels show control (left) and treatment (right) at 24 h (A), 48 h (B), and 72 h (C). Lower panels show higher magnification (40X) of the corresponding time. Seedlings with primary roots were stained for 10–15 minutes with 25 µM DCFDA in distilled water.Clearly, allelochemical stress caused by S. deppei is producing an oxidative imbalance as evidenced by generation of ROS and alteration of activity of antioxidant enzymes. Another result that supports this observation is the high level of lipid peroxidation that we observed at 48 and 72 h, which correlates with the inhibition of two membrane-associated enzymes, H⁺-ATPase¹⁵ and NADPH oxidase.¹⁶ We believe, however, that the oxidative damage we observed is not solely responsible for the phytotoxic effect of S. deppei on tomato growth. In other words, we suggest that its inhibitory effect represents the sum of many metabolic processes affected at different times. Currently we are studying the dynamics of carbohydrate mobilization, cell wall loosing of the endosperm to allow the protrusion of the radicle, and ABA content. Preliminary results have shown that there is a delay in expression of some enzyme activities and a high content of ABA.     

Total antioxidant capacity and nuclear DNA damage in keratinocytes after exposure to H2O2

Studies of oxidative stress have classically been performed by analyzing specific, single antioxidants. In this study, susceptibility to oxidative stress in the human keratinocyte cell line NCTC2544 exposed to hydrogen peroxide (H2O2) was measured by the TOSC (total oxyradical scavenging capacity) assay, which discriminates between the antioxidant capacity toward peroxyl radicals and hydroxyl radical. The generation of H2O2-induced DNA damage, total antioxidant capacity and levels of antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase, glutathione S-transferase, glutathione peroxidase) were studied. Exposure to H2O2-induced DNA damage that was gradually restored while a significant reduction in cellular TOSC values was obtained independently of stressor concentrations and the degree of DNA repair. Whereas TOSC values and cell resistance to H2O2 showed a good relationship, the extent of DNA damage is independent from cellular total antioxidant capacity. Indeed, maximum DNA damage and cell mortality were observed in the first 4 h, whereas TOSC remained persistently low until 48 h. Catalase levels were significantly lower in exposed cells after 24 and 48 h. Keratinocytes exposed after 48 h to a second H2O2 treatment exhibited massive cell death. A possible linkage was observed between TOSC values and NCTC2544 resistance to H2O2 challenge. The TOSC assay appears to be a useful tool for evaluating cellular resistance to oxidative stress.     

Cu/Zn superoxide dismutase (SOD1) induction is implicated in the antioxidative and antiviral activity of acetylsalicylic acid in HCV-expressing cells

We evaluated the participation of oxidative stress in the negative regulation of hepatitis C virus (HCV)-RNA induced by acetylsalicylic acid (ASA). We used the HCV subgenomic replicon cell system that stably expresses HCV-nonstructural proteins (Huh7 HCV replicon cells) and the parental cell line. Cells were exposed to 4 mM ASA at different times (12-72 h), and pyrrolidine dithiocarbamate (PDTC) was used as an antioxidant control. Reactive oxygen species (ROS) production, oxidized protein levels, cytosolic superoxide dismutase (Cu/Zn-SOD), and glutathione peroxidase (GPx) activity were measured to evaluate oxidative stress. In addition, viral RNA and prostaglandin (PGE(2)) levels were determined. We observed that ASA treatment decreased ROS production and oxidized protein levels in a time-dependent fashion in both parental and HCV replicon cells with a greater extent in the latter. Similar results were found with PDTC exposure. Average GPx activity was decreased, whereas a striking increase was observed in average cytosolic SOD activity at 48 and 72 h in both cells exposed to ASA, compared with untreated cells. HCV replicon cells showed higher levels of Cu/Zn-SOD expression (mRNA and protein) with ASA treatment (48 and 72 h), whereas NS5A protein levels showed decreased expression. In addition, we found that inhibition of SOD1 expression reversed the effect of ASA. Interestingly, PDTC downregulated HCV-RNA expression (55%) and PGE(2) (60%) levels, imitating ASA exposure. These results suggest that ASA treatment could reduce cellular oxidative stress markers and modify Cu/Zn-SOD expression, a phenomenon that may contribute to the mechanisms involved in HCV downregulation.     

Involvement of mitochondria in oxidative stress-induced cell death in mouse zygotes

Accumulation of reactive oxygen species during aging leads to programmed cell death (PCD) in many cell types but has not been explored in mammalian fertilized eggs, in which mitochondria are "immature," in contrast to "mature" mitochondria in somatic cells. We characterized PCD in mouse zygotes induced by either intensive (1 mM for 1.5 h) or mild (200 microM for 15 min) hydrogen peroxide (H(2)O(2)) treatment. Shortly after intensive treatment, zygotes displayed PCD, typified by cell shrinkage, cytochrome c release from mitochondria, and caspase activation, then terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining in condensed pronuclei. On the other hand, after mild treatment, zygotes arrested developmentally and showed neither cytochrome c release nor caspase activation over 48 h; until 72 h, 46% zygotes exhibited TUNEL staining, and 88% of zygotes lost plasma membrane integrity. Interestingly, mild oxidative treatment induced a decline in mitochondrial membrane potential and disruption of the mitochondrial matrix. Taken together, these results suggest that oxidative stress caused by H(2)O(2) induces PCD in mouse zygotes and that mitochondria are involved in the early phase of oxidative stress-induced PCD. Furthermore, mitochondrial malfunction also may contribute to cell cycle arrest, followed by cell death, triggered by mild oxidative stress.     

Changes of nitric oxide, carbon monoxide and oxidative stress in term infants at birth

The higher risk of respiratory problem in infants delivered by elective caesarean section in comparison with vaginally born infants may be favoured by lower level of nitric oxide (NO) and carbon monoxide (CO) and higher oxidative stress in infants born by caesarean section. We studied healthy term infants born by vaginal delivery or by elective caesarean section. Nitric oxide, CO, guanosine 3-5 cyclic monophosphate, total hydroperoxide and advanced oxidation protein products (AOPP) were measured at birth and 48-72 h of life. Nitric oxide, CO and cGMP were lower at birth and at 48-72 h of life in infants born by elective caesarean delivery. Total hydroperoxide and AOPP levels were similar in the two groups and increased from birth to 48-72 h of life. In conclusion, nitric oxide and CO concentrations were higher in term infants vaginally born than in infants born by elective caesarean section and decreased from birth to 48-72 h of life. The mode of delivery did not affect the oxidative stress which increases from birth to 48-72 h of life.     

2-Hydroxy-1,4-naphthoquinone, the natural dye of Henna, is non-genotoxic in the mouse bone marrow micronucleus test and does not produce oxidative DNA damage in Chinese hamster ovary cells

2-Hydroxy-1,4-naphthoquinone (HNQ) has been found positive in a previous chromosome aberration test in Chinese hamster ovary (CHO) cells and in a mouse bone marrow micronucleus test at 72h after oral administration (vehicle: DMSO). However it was negative at 24 and 48h sampling times, and in subsequent micronucleus tests that used 0.5% aqueous methyl cellulose (MC) as vehicle. We performed a bone marrow micronucleus test in male and female NMRI BRL/BR mice at oral doses of 75, 150 and 300mg/kg in two vehicles (DMSO and 0.5% aqueous MC), evaluated micronuclei at 24, 48 and 72h, plasma levels of HNQ at 0.5, 1 and 4h, and haematology parameters at 72h after administration. The mechanism of in vitro clastogenic activity of HNQ was investigated by evaluation of the potential of HNQ to produce oxidative DNA damage after treatment of CHO with 10mM HNQ, followed by quantification of DNA fragments using the comet assay. In the micronucleus test, HNQ at 300mg/kg produced mortality and clinical signs at similar incidence and severity for both vehicles. Levels of HNQ in the plasma of treated mice were dose-related, of similar magnitude for both vehicles, but higher in females than in males. Maximum concentrations were found at 0.5 or 1h. At 300mg/kg, HNQ slightly affected RBC parameters suggesting haematotoxicity. No increase in the frequency of micronuclei was observed for any dose, vehicle or time point, whereas the positive control substance (CPA) produced a clear positive response. No evidence of HNQ-induced oxidative DNA damage was found at clastogenic concentrations in vitro, whereas the positive control substance (H(2)O(2)) produced a clear increase. In conclusion, HNQ was negative for induction of bone marrow micronuclei in mice up to 72h after administration in two different vehicles, and its in vitro clastogenicity was not due to oxidative damage. These results confirm that HNQ poses no or negligible genotoxic risk.     

曼陀罗叶水浸液对大豆幼根生长及细胞分裂的影响

以曼陀罗叶干粉为供体,大豆种子为受体,用室内培养皿法研究了曼陀罗叶水浸液化感胁迫对大豆种子萌发、幼根生长、根毛发育和根尖细胞分裂的影响。结果表明:各试验浓度的曼陀罗叶干粉水浸提液均抑制了大豆种子的萌发以及幼根和侧根的生长,且幼根生长随胁迫浓度的增加呈现逐渐缩短变粗变褐的趋势;化感胁迫还使根尖分生区细胞的染色体畸变和微核高频率发生。根毛发生和根尖细胞的分裂对化感胁迫都表现出"低促高抑"的响应,即轻度胁迫能显著促进根毛的生长并提高根尖细胞的分裂指数,而高度胁迫对根毛的生长有极显著的抑制作用,且使根尖细胞的分裂指数显著下降。     

Nitric oxide (as sodium nitroprusside) supplementation ameliorates Cd toxicity in hydroponically grown wheat roots

Cadmium (Cd) is a non-redox toxic heavy metal present in the environment and induces oxidative stress in plants. We investigated whether exogenous nitric oxide (NO) supplementation as sodium nitroprusside (SNP) has any ameliorating action against Cd-induced oxidative damage in plant roots and thus protective role against Cd toxicity. Cd treatment (50 or 250 μM) alone or in combination with 200 μM SNP was given to hydroponically grown wheat roots for a short time period of 24 h and then these were shifted to distilled water to observe changes in levels of oxidative markers (lipid peroxidation, H₂O₂ content and electrolyte leakage). Supplementation of Cd with SNP significantly reduced the Cd-induced lipid peroxidation, H₂O₂ content and electrolyte leakage in wheat roots. It indicated a reactive oxygen species (ROS) scavenging activity of NO. However, even upon removal of Cd-treatment solution, the levels of oxidative markers increased during 24 h recovery stage and later at 48 h these decreased. Cd treatment resulted in an upregulation of activities of antioxidant enzymes—superoxide dismutase (SOD, 1.15.1.1), guaiacol peroxidase (GPX, 1.11.1.7), catalase (CAT, 1.11.1.6), and glutathione reductase (GR, 1.6.4.2). SNP supply resulted in a reduction in Cd-induced increased activities of scavenging enzymes. The protective role of exogenous NO in decreasing Cd-induced oxidative damage was also evident from the histochemical localization of lipid peroxidation, plasma membrane integrity and superoxides. The study concludes that an exogenous supply of NO protects wheat roots from Cd-induced toxicity.     

Azadirachta indica and Ocimum sanctum leaf extracts alleviate arsenic toxicity by reducing arsenic uptake and improving antioxidant system in rice seedlings

In the present study the potentials of aqueous extracts of the two plants, neem (Azadirachta indica) and Tulsi (Ocimum sanctum) were examined in alleviating arsenic toxicity in rice (Oryza sativa L.) plants grown in hydroponics. Seedlings of rice grown for 8 days in nutrient solution containing 50 μM sodium arsenite showed decline in growth, reduced biomass, altered membrane permeability and increased production of superoxide anion (O2·−), H2O2 and hydroxyl radicals (·OH). Increased lipid peroxidation marked by elevated TBARS (thiobarbituric acid reactive substances) level, increased protein carbonylation, alterated levels of ascorbate, glutathione and increased activities of enzymes SOD (superoxide dismutase), CAT (catalase), APX (ascorbate peroxidase) and GPX (glutathione peroxidase) were noted in the seedlings on As treatment. Exogenously added leaf aqueous extracts of Azadirachta indica (0.75 mg mL−1, w/v) and Ocimum sanctum (0.87 mg mL−1, w/v) in the growth medium considerably alleviated As toxicity effects in the seedlings, marked by reduced As uptake, restoration of membrane integrity, reduced production of ROS, lowering oxidative damage and restoring the levels of ascorbate, glutathione and activity levels of antioxidative enzymes. Arsenic uptake in the seedlings declined by 72.5% in roots and 72.8% in shoots, when A. indica extract was present in the As treatment medium whereas with O. sanctum extract, the uptake declined by 67.2% in roots and 70.01% in shoots. Results suggest that both A. indica and O. sanctum aqueous extracts have potentials to alleviate arsenic toxicity in rice plants and that A. indica can serve as better As toxicity alleviator compared to O. sanctum.     

Induction of oxidative stress and DNA damage in cervix in acute treatment with benzo[a]pyrene

Benzo[a]pyrene [B(a)P] is one of the most prevalent environmental carcinogens and genotoxic agents. However, the mechanisms of B(a)P-induced oxidative damage in cervical tissue are still not clear. The present study was to investigate the oxidative stress and DNA damage in cervix of ICR female mice induced by acute treatment with B(a)P. Oxidative stress was assayed by analysis of malondialdehyde (MDA), superoxide anion and H(2)O(2), and antioxidant enzymes. The alkaline single-cell electrophoresis (SCGE) was used to measure DNA damage. The contents of MDA and glutathione (GSH), and the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST) were significantly increased in cervix 24, 48 and 72h after B(a)P treatment of a single dose of 12.5 and 25mg/kg, while GSH, CAT, SOD and GST had no significant difference with the dose of 50mg/kg B(a)P at post-treatment time 48 and 72h except for SOD activity at 48h which was significant. The maximum values of SOD, CAT, GST and GSH were peaked at 24h and then decreased gradually while GPx activities and MDA levels persisted for up to 72h. Superoxide anion, H(2)O(2) and DNA damage changed similarly as the activity of SOD, CAT or GST. Additionally, increases of formamidopyrimidine DNA glycosylase (FPG) specific DNA damage were observed and can be greatly rescued by vitamin C pretreatment. Overall, B(a)P demonstrated a time- and dose- related oxidative stress and DNA damage in cervix.     

Inhibitory effects of leachate from Eupatorium adenophorum on germination and growth of Amaranthus retroflexus and Chenopodium glaucum

Amaranthus retroflexus L. and Chenopodium glaucum L. are two widely distributed destructive weeds. Their strong adaptability and massive seed production make them the hardest weeds to deal with. This present study intended to investigate the effect of leachate from Eupatorium adenophorum on the growth of these weeds and explore the potential to develop an environmental friendly strategy to use the leachate to control the weeds. Seeds of A. retroflexus L. and C. glaucum L. were soaked in solutions containing 0%, 0.6%, 1.25%, 2.5%, and 5% leachate from E. adenophorum leaves. A. retroflexus and C. glaucum seedlings grown in pots were sprayed with leachate solutions in the same concentration range. The effects of these leachate solutions on membrane permeability and germination of seeds, and growth and physiological characteristics of the seedlings were investigated. The highest concentration of leachate (5%) caused significant damage to the cell membrane of seeds of both weed species, whereas lower concentrations (0.6%) promoted repair of the membrane system, as reflected by higher and lower than control in relative conductivity (RC), respectively. Different concentrations of leachate showed distinct allelopathic inhibitory effects on the two weed species; lower concentrations showed weak inhibitory or even positive effects, whereas higher concentrations showed stronger inhibitory effects. Higher concentrations of leachate (2.5% and 5%) delayed germination and significantly decreased the emergence rate of the seeds, survival rate, and dry matter accumulation of the seedlings. When treated by 5% leachate, the emergence date of A. retroflexus was delayed by 3.6 d, emergence rate of the seeds and survival rate was 69.1% and 70.6% of the control, respectively, seedling dry matter was 48.6% less than the control; In the case of C. glaucum, the emergence date was delayed by 2.7 d, emergence rate of the seeds and survival rate was 45.1% and 58.6% of the control, respectively, seedling dry matter was 44.7% less than the control. There were significant interactions among the different concentrations of leachate and the length of treatment period with respect to activities of antioxidant enzymes, malondialdehyde (MDA) contents, and chlorophyll contents. Seedlings treated with 0.6%, 1.25%, or 2.5% leachate solution for 24–72 h showed increased superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities. When seedlings were treated with leachate solutions for 96 h, antioxidant enzyme activities and chlorophyll content decreased in A. retroflexus, but only CAT activity decreased in C. glaucum. When seedlings of the two weed species were treated with 5% leachate solution, CAT activity and chlorophyll content decreased and MDA content gradually increased with longer treatment times (from 24 to 96 h). The two weed species showed different allelopathic responses to E. adenophorum; A. retroflexus was more sensitive than C. glaucum. Based on the investigation, it could be speculated that the delayed germination and low germination rate of the weeds after treatment by leachate could be due to the fact that leachate damaged the membrane system of the seeds. By delaying germination, lowering the germination rate of the weeds and inhibiting seedling growth, leachate from E. adenophorum could provide an effective way of controlling the weeds.     

The root-colonizing endophyte Pirifomospora indica confers drought tolerance in Arabidopsis by stimulating the expression of drought stress-related genes in leaves

Piriformospora indica is an endophytic fungus that colonizes the roots of many plant species, including Arabidopsis. We exposed 18-day-old Arabidopsis seedlings, which were either cocultivated with the fungus or mock-treated for the last 9 days, to mild drought stress for 84 h. During the first 36 to 48 h, seedlings cocultivated with the fungus continued to grow, while the uncolonized controls did not. This results in a threefold difference in the fresh weight and a more than twofold difference in the chlorophyll content. The photosynthetic efficiency was only slightly reduced in the colonized (F variable/F maximum [Fv/Fm] at t(0 h) = 0.82 and t(36 h) = 0.79) and was severely impaired in the uncolonized (Fv/Fm at t(0 h) = 0.81 and (t)(36 h) = 0.49) seedlings, which also showed symptoms of withering. When seedlings exposed to drought stress for 72 or 84 h were transferred to soil, 10% (72 h) and none (84 h) of uncolonized seedlings reached the flowering stage and produced seeds, while 59% (72 h) and 47% (84 h) of the colonized seedlings flowered and produced seeds. After exposure to drought stress for 3 h, the message levels for RESPONSE TO DEHYDRATION 29A, EARLY RESPONSE TO DEHYDRATION1, ANAC072, DEHYDRATION-RESPONSE ELEMENT BINDING PROTEIN2A, SALT-, AND DROUGHT-INDUCED RING FINGER1, phospholipase Ddelta, CALCINEURIN B-LIKE PROTEIN (CBL)1, CBL-INTERACTING PROTEIN KINASE3, and the histone acetyltransferase (HAT) were upregulated in the leaves of P. indica-colonized seedlings. Uncolonized seedlings responded 3 to 6 h later, and the message levels increased much less. We identified an Arabidopsis ethylmethane-sulfonate mutant that is less resistant to drought stress and in which the stress-related genes were not upregulated in the presence of P. indica. Thus, P. indica confers drought-stress tolerance to Arabidopsis, and this is associated with the priming of the expression of a quite diverse set of stress-related genes in the leaves. Transfer to soil was again associated with a faster and stronger upregulation of the message levels for phospholipase Ddelta, CBL1, and HAT in P. indica-colonized seedlings, indicating that this response might also contribute to better survival on soil.     

水分胁迫对小麦根细胞质膜氧化还原系统的影响

水分胁迫使小麦根质膜ＮＡＤＨ和ＮＡＤＰＨ的氧化速率及Ｆｅ（ＣＮ）６３－和ＥＤＴＡ－Ｆｅ３＋的还原速率明显降低。对照与胁迫处理的质膜氧化还原系统活性均不受鱼藤酮抗霉素Ａ和ＫＣＮ等呼吸链抑制剂的影响。在不加Ｆｅ（ＣＮ）６３－作为电子受体时,水杨基羟肘酸（ＳＨＷ）可明显刺激质膜ＮＡＤＨ的氧化和Ｏ２吸收速率。水分胁迫促使ＳＨＡＭ刺激的ＮＡＤＨ氧化明显降低,但却使Ｏ２吸收略有上升。