Environmental Stresses and Redox Status of Ascorbate

To investigate the effects of environmental stresses on ascorbic acid content and its redox status, the effects of freezing and drought on ascorbate and dehydro-ascorbate content and activities of four enzymes involved in the ascorbate-glutathione cycle in some conifers were studied. The results showed that both freezing and drought induced the decrease in ascorbate content and the increase in dehydro-ascorbate content. The activities of ascorbate peroxidase (APX) and monodehydro-ascorbate reductase (MDAR) were decreased by freezing stress. At the beginning of exposure to air, water loss from detached needles induced the increase in the activities of APX and MDAR. Further water loss turned to decrease the APX and MDAR activities. The activities of dehydro-ascorbate reductase (DHAR) and glutathione reductase (GR) were not sensitive to changes in temperature and water content of the needles. It is concluded that moderate temperature or water stresses may induce the acclimation and increase in the ability of the H2O2 scavenging system, while strong stresses decrease the ability and induce injury of plant tissues. Correlation between ascorbate content and activities of related enzymes and cold tolerance of conifers were also reported.

Effects of Catalase and Ascorbate Peroxidase on the Root Growth of Rice under Cadmium Stress

[Objective] The research aimed to study the correlations between catalase（CAT） and ascorbate peroxidase（ASP） and the growth and development of rice roots under cadmium stress.[Method] Taking rice variety Zhonghua No.11 as materials,the changes of rice seedlings under the treatment conditions of Cd,Cd＋CAT inhibitor,Cd＋APX inhibitor were studied.[Result] Under Cd stress,inhibition of CAT activity caused the significant inhibition on the growth of aerial parts,decreased the number of adventitious roots and lateral roots,but it can significant promote the elongation growth of adventitious roots and lateral roots.Moreover,the length of the first lateral root from root tip on the primary roots and adventitious roots was also increased than control.When APX activity was inhibited,the growth changes of rice were similar with that treated by CAT inhibitor.[Conclusion] CAT and APX may play important roles in the regulation of rice root system growth in both non-stress and Cd-stressed rice

Cold acclimation improves photosynthesis by regulating the ascorbate–glutathione cycle in chloroplasts of Kandelia obovata

As the most northerly mangrove species in China, Kandelia obovata may undergo extreme cold event stress. Enhancing the cold tolerance of this species is crucial to its successful afforestation. This study aimed to determine the resistance of K. obovata seedlings to low temperature stress by cold acclimation and to explain the mechanisms for alleviating cold injury. To understand these mechanisms, seedlings that were acclimatized and not acclimatized were exposed to 5℃/- 2℃(day/night)for 48 h.Results showed that low temperature stress reduced leaf photosynthesis of non-acclimatized seedlings by inducing oxidative stress and structural damage to chloroplasts. These phenomena were shown by increasing levels of malondialdehyde (MDA), O2-and H2O2, as well as decreasing enzyme activities in the ascorbate–glutathione (AsA-GSH) cycle. However, cold-acclimatized seedlings had improved photosynthetic rates and efficiency of photosystem II (PSII) under low temperature stress. Compared with non-acclimatized seedlings, leaves of coldacclimatized seedlings under low temperature stress for 48 h exhibited higher anti-oxidative enzyme activities, lower levels of O2^- and H2O2, less damage to chloroplast structure, and removed 33.7% of MDA at low temperature stress for 48 h. The data indicate that cold acclimation enhances photosynthetic capacity by effectively regulating activation in the PSII electron transport and the AsA–GSH cycle to scavenge excess ROS in chloroplasts, while the latter is more important.

Mechanisms of Salt Tolerance in Transgenic Arabidopsis thaliana Carrying a Peroxisomal Ascorbate Peroxidase Gene from Barley

Ascorbate peroxidases （APX）, localized in the cytosol, peroxisome, mitochondria, and chloroplasts of plant cells, catalyze the reduction of H2O2 to water by using ascorbic acid as the specific electron donor. To determine the role of peroxisomal type ascorbate peroxidase （pAPX）, an antioxidant enzyme, in protection against salt-induced oxidative stress, transgenic Arabidopsis thaliana plant carrying a pAPX gene （HvAPX1） from barley （Hordeum vulgate L.） was analyzed. The transgenic line pAPX3 was found to be more tolerant to salt stress than the wild type. Irrespective of salt stress, there were no significant differences in Na^＋, K^＋, Ca^2＋, and Mg^2＋ contents and the ratio of K^＋ to Na^＋ between pAPX3 and the wild type. Clearly, the salt tolerance in pAPX3 was not due to the maintenance and reestablishment of cellular ion homeostasis. However, the degree of H2O2 and lipid peroxidation （measured as the levels of malondialdehyde） accumulation under salt stress was higher in the wild type than in pAPX3. The mechanism of salt tolerance in transgenic pAPX3 can thus be explained by reduction of oxidative stress injury. Under all conditions tested, activities of superoxide, glutathione reductase, and catalase were not significantly different between pAPX3 and the wild type. In contrast, the activity of APX was significantly higher in the transgenic plant than in wild type under salt stress. These results suggested that in higher plants, HvAPX1 played an important role in salt tolerance and was a candidate gene for developing salttolerant crop plants.

Over-Expression of Tomato GDP-Mannose Pyrophosphorylase (GMPase) in Potato Increases Ascorbate Content and Delays Plant Senescence

GDP-D-mannose pyrophosphorylase （GMPase） catalyses the synthesis of GDP-D-mannose and represents the first committed step in the synthesis of ascorbate. In the present study, the GMPase gene of tomato was introduced into potato by Agrobacterium-mediated transformation. Two transgenic lines with higher GMPase expression were selected using qPCR and protein blot analyses. The results showed that the content of L-ascorbic acid （AsA） and the ratio of AsA/ DHA （dehydroascorbate） significantly increased in both leaves and tubers of transgenic potato plants. Both pigment content and photosynthetic rate were much higher in transgenic plants than in wild-type plants. Transgenic plants showed a distinguishable change in phenotype from the wild-type plants. Furthermore, transgenic plants showed delayed senescence.

Overexpression of a Cytosolic Ascorbate Peroxidase Gene, OsAPX2, Increases Salt Tolerance in Transgenic Alfalfa

Alfalfa （Medicago sativa L.） is an important forage crop in the world and it is of great signiifcance for the improvement of its salt tolerance. To improve salt tolerance in alfalfa, a rice ascorbate peroxidase gene （OsAPX2） was introduced into alfalfa using Agrobacterium tumefaciens-mediated transformation with marker gene bar. The different T-DNA insertions in T1 transgenic alfalfa were identiifed by Southern hybridization. Three independent T2 transgenic lines were selected for stress analysis and the results showed that all of them were salt tolerant compared with wild-type plants. The transgenic plants had low levels of H2O2, malondialdehyde and relative electrical conductivity under salt and drought stresses. Moreover, the contents of chlorophyll and proline, and APX activity were high in transgenic plants under salt and drought stresses. Taken together, the overexpression of OsAPX2 enhances salt tolerance in alfalfa through scavenging reactive oxygen species.

Differential Expression of Two Cytosolic Ascorbate Peroxidases and Two Superoxide Dismutase Genes in Response to Abiotic Stress in Rice

Superoxide dismutase (SOD) and ascorbate peroxidase (APX) play central roles in the pathway for scavenging reactive oxygen species in plants, thereby contributing to the tolerance against abiotic stress. Here we report the responses of cytosolic SOD (cSOD; sodCc1 and sodCc2) and cytosolic APX (cAPX; OsAPX1 and OsAPX2) genes to oxidative and abiotic stress in rice. RNA blot analyses revealed that methyl viologen treatment caused a more prominent induction of cAPXs compared with cSODs, and hydrogen peroxide treatment induced the expression of cAPXs whereas cSODs were not affected. These results suggest that cAPXs play more important roles in defense against oxidative stress compared with cSODs. It is noted that cSODs and cAPXs showed coordinate response to abscisic acid treatment which induced both sodCc1 and OsAPX2. However, cSODs and cAPXs responded differentially to drought, salt and chilling stress, which indicates that cSOD and cAPX genes are expressed differentially in response to oxidative and abiotic stress in rice.

Kiwifruit(Actinidia chinensis 'Hongyang') cytosolic ascorbate peroxidases(AcAPX1 and AcAPX2) enhance salinity tolerance in Arabidopsis thaliana

Ascorbate peroxidase(APX) plays a key role in scavenging reactive oxygen species(ROS) in higher plants. However, there is very little information available on the APXs in kiwifruit(Actinidia), which is an economically and nutritionally important horticultural crop with exceptionally high ascorbic acid(AsA) accumulation. This study aims to identify and characterize two cytosolic APX genes(AcAPX1 and AcAPX2) derived from A. chinensis ‘Hongyang’. The constitutive expression pattern was determined for both AcAPX1 and AcAPX2, and showed relatively higher expression abundances of AcAPX1 in leaf and AcAPX2 in root. Transcript levels of AcAPX1 and AcAPX2 were increased in kiwifruit roots treated with Na Cl. Subcellular localization assays using GFP-fusion proteins in Arabidopsis protoplasts showed that both AcAPX1 and AcAPX2 are targeted to the cytosol. Recombinant AcAPX1 or AcAPX2 proteins were successfully expressed in the prokaryotic expression system and their individual ascorbate peroxidase activities were determined. Finally, constitutive over-expression of AcAPX1 or AcAPX2 could dramatically increase total As A, glutathione level and salinity tolerance under Na Cl stress in Arabidopsis thaliana. Our findings revealed that cytosolic AcAPX1/2 may play an important protective role in the responses to unfavorable environmental stimuli in kiwifruit.

SYNTHESIS OF DIAMMINEPLATINUM(Ⅱ)ASCORBATE AND STRUCTURE COMPARISON WITH ITS DACH DERIVATIVES

An antitumour complex,cis-diammineplatinum(Ⅱ)ascorbate,has been synthesized and its X-ray structure is given.Quantum chemistry calculation compared with its diaminecyclohexane derivatives indicates that they have different electron distribution.

Cytological Investigation of Pollen Development in Sorghum Line with Male Sterility Induced by Sodium Ascorbate in Tissue Culture

Investigation of male sterility mutations is an effective approach for identification of genes involved in anther and pollen development. The comparison of “cytological phenotypes” of newly induced mutants with phenotypes determined by already known genes favors elucidation of genetic control of diverse microsporo- and gametogenesis stages. In this paper, we describe pollen development in the grain sorghum line Zh10-asc1 with mutation of male sterility. This line was obtained from callus culture treated by sodium ascorbate. A wide spectrum of abnormalities in microsporogenesis have been found, such as cytomixis, chromosomal laggards, chromosome disjunction, adhesion of chromosomes, disturbed cytokinesis, and others. In tapetum, the cells with one nucleus, with unequal nuclei, and with micronuclei have been observed. During pollen grain (PG) maturation abnormalities in starch accumulation and delay of development often took place. In mature anthers, a variety of pollen grain types have been revealed: fertile, of irregular shape, incompletely filled with starch, PGs delayed at the uni-nucleate or bi-nucleate gametophyte stages, with partially or fully degenerated contents, and with abnormal coloration. Variation in spectrum and the frequency of disturbances between the flowers of one and the same plant have been revealed. The reasons for significant genetic and epigenetic instability are discussed.

Megadoses of Sodium Ascorbate Efficiently Kill HL60 Cells <i>in Vitro</i>: Comparison with Arsenic Trioxide

Arsenic Trioxide (ATO) is widely acknowledged as the treatment of choice for Acute Promyelocytic Leukemia (APL). It is a “two-sided” drug since it can induce differentiation or kill APL and other tumor cells according to the dosage. Part of the cytotoxic effects of ATO on APL cells is due to its pro-oxidant activity, a characteristic which ATO shares with a number of other compounds, including high doses of ascorbate (ASC). In a comparative investigation on the cytotoxic effects of both ATO and ASC on HL60 (APL) cell lines, in Vitro, we have been able to confirm the known cytotoxic effects of ATO, but, more importantly, we have demonstrated that ASC is significantly more effective than ATO, in killing these cancer cells in Vitro, when the concentrations are maintained within the millimolar (mM) range, i.e. the range of plasma concentrations at which ASC induces oxidative damage to tumor cells. Since these plasma levels can be reached only by the intravenous administration of high doses of ASC, we propose that intravenous high doses of ASC may represent a potentially revolutionary new approach in the management of APL.

Ascorbate-Glutathione Cycle Alteration in Cadmium Sensitive Rice Mutant cadB-1

A rice cadmium （Cd） sensitive mutant cadB-1 was obtained using Agrobacterium tumefaciens mediated system.After exposure of cadB-1 and wild type （WT） rice seedlings to a range of Cd concentrations for 10 d,Cd accumulated to higher levels in roots,stems and leaves of both cadB-1 and WT with increasing external Cd concentrations,and the inhibition of seedling growth in cadB-1 was more serious than in WT.Hydrogen peroxide accumulation was higher in leaves and roots of cadB-1.The ratios of reduced glutathione （GSH）/oxidized glutathione （GSSG）,ascorbate （ASC）/dehydroascorbate （DHA） and reduced nicotinamide adenine dinucleotide phosphate （NADPH）/oxidized nicotinamide adenine dinucleotide phosphate （NADP＋） were lower in cadB-1 than in WT both in leaves and roots under high Cd levels.The activities of ascorbate peroxidase （APX）,glutathione peroxidase （GR）,dehydroascorbate reductase （DHAR） and monodehydroascorbate reductase （MDHAR） were also lower in cadB-1 than in WT both in leaves and roots under the treatment of high levels of Cd.Our results suggest that under Cd stress,the ASC-GSH cycle was more seriously inhibited in cadB-1 than in WT,indicating that the mutant cadB-1 is less able to scavenge reactive oxygen species and sensitive to Cd.

Toxicity of Nonylphenol on Microcystis aeruginosa Mediated by the Ascorbate-glutathione (AsA-GSH ) Cycle

Nonylphenol( NP) is a stable metabolic product of nonylphenol ethoxylates,which is widely used as an industrial surfactant. NP has been classified as an endocrine disrupter,and its toxicity to organisms can be biomagnified through the food chain. As compared with the endocrine disrupting effect,the toxicity of NP to organisms has not been studied intensively,and the toxicity mechanisms have often been ignored. In the present study,Microcystis aeruginosa,a freshwater alga belonging to the first level of the trophic chain,was chosen to detect the toxicity of NP. The mechanisms of toxicity mediated by the AsA-GSH cycle were explored. The acute toxicity of NP to M. aeruginosa within 96 h was studied and an EC_(50) concentration of 3. 45 mg/L was found. Further,the results showed that the toxicity of NP increased with the increase in concentration and exposure time. As compared with that in the control,the APX and MDHAR activities mostly increased,whereas DHAR activity fluctuated.However,the AsA content elevated at first,but decreased significantly after 72 h. For the GSH system,GR activity was always higher than that in the control. Nevertheless,the reduced GSH content was mostly inhibited. Therefore,the performance of AsA-GSH antioxidant defense system could explain the results of NP toxicity: the enzyme activities and antioxidant molecules increased initially,but an overall decline appeared after exposure for 24 h. This research is helpful for estimating the toxicity of NP integrally and improves people's understanding of mechanisms of NP toxicity in algae.

智能手机辅助双探针比色法检测α-葡萄糖苷酶

该文以3,3',5,5'-四甲基联苯胺(TMB)和罗丹明B为比色探针,建立了α-葡萄糖苷酶的比色检测方法,并在此基础上基于智能手机策略,通过RGB值对α-葡萄糖苷酶进行检测。结果表明,Fe^(3+)-TMB-罗丹明B显色体系的吸光度与α-葡萄糖苷浓度在20~100 U/L范围内呈线性关系,检出限为3.3 U/L。采用photo⁃shop软件分析样品图像和样品荧光图像的RGB值,其与α-葡萄糖苷酶浓度在10~100 U/L范围内呈线性关系,检出限分别为2.5 U/L和1.2 U/L。该法已成功用于α-葡萄糖苷酶抑制剂阿卡波糖抑制率评估和胎牛血清中α-葡萄糖苷酶浓度的测定。所构建的智能手机辅助检测法为α-葡萄糖苷酶的临床分析和酶抑制剂的快速筛选提供了简便、快捷和准确的方法。

抗坏血酸对番茄红素染色性能的影响

为研究番茄红素对织物的染色可行性,以抗坏血酸作为色素稳定剂,用番茄红素对涤纶仿真丝织物进行染色试验,并对染色织物的染色牢度进行评价。利用吸光度值讨论抗坏血酸对番茄红素色素稳定性的影响,根据染色织物的K/S值和L^(*)、a^(*)、b^(*)值研究了染色织物的染色性能,并测定染色织物的色牢度。结果表明:抗坏血酸能提高番茄红素色素的稳定性,对番茄红素起到护色作用;在染色过程中,抗坏血酸的加入能提高染色织物的K/S值,但过量的加入并不能起到增深的作用;染色织物具有一定的色牢度。

镍锰氧化物复合电化学传感器对抗坏血酸的检测

首先,通过一步水热法制备了镍锰氧化物复合材料(Mn-Ni-Oxide),并将其修饰玻碳电极构建抗坏血酸快速检测的电化学传感器。利用XRD、SEM、EDS及FTIR对Mn-Ni-Oxide进行了表征。采用滴涂法将Mn-Ni-Oxide修饰于电极表面,并用循环伏安(CV)法、差分脉冲伏安(DPV)法测试了抗坏血酸在Mn-Ni-Oxide修饰电极上的电化学行为。结果表明,Mn-Ni-Oxide的外表面为带有孔隙的纳米球形结构,主要组分为Mn_(2)O_(3)、NiMnO_(3)。在pH为4的乙酸/乙酸钠缓冲溶液条件下,修饰电极的Mn-Ni-Oxide修饰量为10μL,抗坏血酸浓度(c)在0.1~9000μmol/L时与氧化峰电流(I_(p))呈线性关系,线性方程为I_(p)=3.2435c+17.198(R^(2)=0.9920),检出限为0.025μmol/L,灵敏度为3.2435μA·m·L/(mol·cm)。该传感器实际应用于果汁饮料中抗坏血酸的测定,加标回收率为95.5%~103.1%,表明其在食品分析等方面具有良好的应用前景。

抗坏血酸提高棉花种子萌发耐盐性及其生理机制

本研究以新疆主栽棉花品种‘新陆早61号’为材料,旨在探讨抗坏血酸(AsA)浸种对提高棉花种子萌发期耐盐性的效果及其生理机制。通过分析不同类型盐胁迫(NaCl、Na_(2)SO_(4)和Na_(2)CO_(3)+NaHCO_(3))下,抗坏血酸(AsA)浸种对棉花种子(棉种)主要发芽特性和生理指标的影响。结果表明,棉种的萌发随盐胁迫浓度升高而下降;但在AsA浸种处理后,棉种萌发特性显著增强,其中发芽率分别比对照提高了55.32%、56.10%和44.0%。最佳AsA浸种浓度分别为0.10 mmol/L(NaCl和Na_(2)SO_(4))和0.15 mmol/L(Na_(2)CO_(3)+NaHCO_(3))。此外,盐胁迫萌发过程中AsA浸种提高了棉种SOD、POD、CAT抗氧化酶的活性,增强了可溶性蛋白和可溶性糖的含量,同时降低了MDA和H_(2)O_(2)的水平。研究表明,AsA浸种通过增强抗氧化酶活性、增加渗透物质含量和减少膜脂过氧化,有效提升了棉花种子的耐盐性。

复配保鲜剂处理对鲜切生菜的护色效果

为明确柠檬酸与抗坏血酸钙复配处理对鲜切生菜的护色效果,将质量分数分别为0.1%,0.2%的柠檬酸与质量分数分别为0.5%,1.5%,2.5%的抗坏血素酸钙复配成6种保鲜剂,然后分别浸泡处理鲜切生菜2 min,定期测定生菜的感官品质、失重率、褐变指数、维C含量。结果表明,在4℃条件下,柠檬酸与抗坏血酸钙复配处理对鲜切生菜的护色效果显著,且能维持鲜切生菜良好的感官品质和较高的维C含量。其中,以0.1%柠檬酸+0.5%抗坏血酸钙、0.1%柠檬酸+2.5%抗坏血酸钙复配处理表现最好,保鲜期14 d。建议生产上采用0.1%柠檬酸+0.5%抗坏血酸钙复配对鲜切生菜进行护色,7 d内生菜褐变指数最低为13.7%,14 d时褐变指数为16.7%,且感官品质佳,无腐烂、萎蔫、黄化。该研究结果为鲜切生菜的加工护色提供了有效参考。

L-抗坏血酸联合超声处理对鲜切芋艿贮藏品质的影响

为探究L-抗坏血酸(L-ascorbic acid,AA)联合超声(ultrasound,US)(AS)处理对鲜切芋艿片贮藏品质的影响,本实验以永定六月红芋为材料,采用质量分数为2%的AA溶液浸泡15 min后,进行US(53 kHz、400 W、10 min)处理,测定贮藏期间鲜切芋艿感官品质及褐变相关酶等指标。结果表明:与对照组相比,AS处理可以降低鲜切芋艿的失水率,维持较高的硬度,延缓褐变指数升高,降低细胞膜通透性,抑制丙二醛含量累积,抑制表面微生物繁殖,从而维持鲜切芋艿较高的感官品质;与对照组相比,贮藏期间AS处理组还能维持较高的过氧化氢酶、超氧化物歧化酶活性,降低过氧化物酶、多酚氧化酶和苯丙氨酸解氨酶活性,抑制酚类物质消耗速率,并减缓淀粉、可溶性蛋白、可溶性固形物等营养物质的流失速率,抑制可溶性醌的积累,延缓风味劣变。上述结果表明,AS处理能够保持鲜切芋艿较好的贮藏品质。

真空预冷对采后娃娃菜流通及货架品质的影响

为优选娃娃菜真空预冷的处理条件,维持采后娃娃菜的新鲜品质,在分析不同真空预冷终温(0、2和4℃)和不同真空预冷终压(400、600、800和1000 Pa)对采后娃娃菜预冷效果的基础上,进行了二因素三水平的中心复合响应面试验。结果显示,与不经预冷处理的对照和终温0℃的预冷组相比,在终压600 Pa条件下,2~4℃的预冷终温处理可更好地维持采后娃娃菜的外观品质,抑制其呼吸速率和丙二醛(MDA)含量的升高。在终温2℃条件下,与不经预冷处理的对照和终压1000 Pa的预冷组相比,400~800 Pa的预冷终压处理可更好地维持采后娃娃菜的外观品质,抑制其呼吸速率及MDA含量的升高。进一步的中心复合响应面试验结果显示,采后娃娃菜的真空预冷最优条件为终温4.0℃、终压600 Pa,该真空预冷条件不仅可维持采后娃娃菜的较好品质,而且可使活性物质可溶性蛋白、总酚和抗坏血酸的含量分别提高18.78%、18.47%和33.23%。因此,适宜的真空预冷处理是一种极具潜力的商品化处理技术,能有效维持采后娃娃菜在流通及货架期间的良好品质。