Universal vectors for constructing artificial microRNAs in plants

Universal amiRNA vectors (pUAs) for constructing plant amiRNAs in Arabidopsis and rice have been developed. By using type IIg restriction enzyme, BaeI, a single amiRNA construct can be produced using only one PCR and one ligation reaction. Thus, only one pair of primers is required for each amiRNA vector and these can be designed to be compatible with existing or newly developed methods. Because the BaeI recognition sequence is completely digested, there is no modification to the miRNA backbone, therefore avoids the risk of sequence changes that may affect downstream analysis. Based on these vectors, specific amiRNA constructs were created and verified. With optimized parameters, 38–45 % colonies for each amiRNA construct contain insertions with the expected orientation, and approximately 80 % of these colonies have the correct sequences.     

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.     

Modulation of Exogenous Glutathione in Ultrastructure and Photosynthetic Performance Against Cd Stress in the Two Barley Genotypes Differing in Cd Tolerance

Greenhouse hydroponic experiments were conducted using Cd-sensitive (Dong 17) and tolerant (Weisuobuzhi) barley genotypes to evaluate genotypic differences in response of photosynthesis and ultrastructure to Cd toxicity in the presence of exogenous glutathione (GSH). Addition of 20 mg L(-1) GSH in 5 μM Cd culture medium (Cd?+?GSH) significantly alleviated Cd-induced growth inhibition and reduced Cd concentration in leaves and roots especially in the sensitive genotype Dong 17. Exogenous GSH greatly ameliorated Cd-induced damages on leaf/root ultrastructure, e.g., compared with Cd alone treatment, chloroplasts in plants treated with Cd?+?GSH become better or in relatively normal shape with well-structured thylakoid membranes and parallel pattern of lamellae and unfolded more starch grains but less osmiophilic plastoglobuli; nuclei of root cells were better formed and chromatin distributed more uniformly in both genotypes, and number of plastids and mitochondria cristae in Dong 17 resumed to control level. The examination of photosynthetic performance revealed GSH dramatically increased net photosynthetic rate (P(n)), stomatal conductance (G(s)), and transpiration rate (T(r)) in the both genotypes and strongly stimulated Cd-induced decrease in the maximal photochemical efficiency (F(v)/F(m)) especially in the sensitive genotype.     

Protective Effect of Selenium on Aflatoxin B1-Induced Testicular Toxicity in Mice

Aflatoxins have been considered as one of the major risk factors of male infertility, and aflatoxin B1 (AFB1) is the most highly toxic and prevalent member of the aflatoxins family. Selenium (Se), an essential nutritional trace mineral for normal testicular development and male fertility, has received extensive intensive on protective effects of male reproductive system due to its potential antioxidant and activating testosterone synthesis. To investigate the protective effect of Se on AFB1-induced testicular toxicity, the mice were orally administered with AFB1 (0.75 mg/kg) and Se (0.2 mg/kg or 0.4 mg/kg) for 45 days. We found that that Se elevated testes index, sperm functional parameters (concentration, malformation, and motility), and the level of serum testosterone in AFB1-exposed mice. Moreover, our results showed that Se attenuated the AFB1-induced oxidative stress and the reduction of testicular testosterone synthesis enzyme protein expression such as steroidogenic acute regulatory protein (StAR), P450 side-chain cleavage (P450scc), and 17β-hydroxysteroid dehydrogenase (17β-HSD) in AFB1-exposed mice. These results demonstrated that Se conferred protection against AFB1-induced testicular toxicity and can be attributed to its antioxidant and increased testosterone level by stimulating protein expression of StAR and testosterone synthetic enzymes.     

Comparative physiological analysis in the tolerance to salinity and drought individual and combination in two cotton genotypes with contrasting salt tolerance

Soil salinity and drought are the two most common and frequently co‐occurring abiotic stresses limiting cotton growth and productivity. However, physiological mechanisms of tolerance to such condition remain elusive. Greenhouse pot experiments were performed to study genotypic differences in response to single drought (4% soil moisture; D) and salinity (200 mM NaCl; S) stress and combined stresses (D + S) using two cotton genotypes Zhongmian 23 (salt‐tolerant) and Zhongmian 41 (salt‐sensitive). Our results showed that drought and salinity stresses, alone or in combination, caused significant reduction in plant growth, chlorophyll content and photosynthesis in the two cotton genotypes, with the largest impact visible under combined stress. Interestingly, Zhongmian 23 was more tolerant than Zhongmian 41 under the three stresses and displayed higher plant dry weight, photosynthesis and antioxidant enzymes activities such as superoxide dismutase (SOD), peroxidase (POD) catalase (CAT) and ascorbate peroxidase (APX) activities compared to control, while those parameters were significantly decreased in salt‐stresses Zhongmian 41 compared to control. Moreover, Na⁺/K⁺‐ATPase activity was more enhanced in Zhongmian 23 than in Zhongmian 41 under salinity stress. However, under single drought stress and D + S stress no significant differences were observed between the two genotypes. No significant differences were detected in Ca²⁺/Mg²⁺‐ATPase activity in Zhongmian 41, while in Zhongmian 23 it was increased under salinity stress. Furthermore, Zhongmian 23 accumulated more soluble sugar, glycine‐betaine and K⁺, but less Na⁺ under the three stresses compared with Zhongmian 41. Obvious changes in leaf and root tips cell ultrastructure was observed in the two cotton genotypes. However, Zhongmian 23 was less affected than Zhongmian 41 especially under salinity stress. These results give a novel insight into the mechanisms of single and combined effects of drought and salinity stresses on cotton genotypes.     

不同镉水平下大麦幼苗生长和镉及养分吸收的品种间差异

利用水培试验研究了不同Cd水平下大麦幼苗的Cd和几种矿质元素吸收、积累、生长和生物学产量的品种间差异 .结果表明 ,1μmol·L-1Cd处理显著降低麦苗株高、绿叶数、叶绿素计读数、地上部和根系干重 ,显著抑制植株对Zn、Mn、Cu的吸收和累积 ;品种之间存在着显著差异 ,无芒六棱受抑制最为严重 ,米麦 114和浙农 1号表现出相对较强的抗性 .麦苗Cd含量和累积量品种之间也有显著差异 ,浙农 1号的Cd含量最高 ,米麦 114最低 .相关分析表明 ,麦苗生物学产量与地上部Cd含量、累积量及根系Cd含量呈显著负相关 ,其中与地上部Cd含量的相关性最强 ,与根系Cd累积量无显著相关 .     

Glutathione-Mediated Alleviation of Chromium Toxicity in Rice Plants

A hydroponic experiment was conducted to determine the possible effect of exogenous glutathione (GSH) in alleviating chromium (Cr) stress through examining plant growth, chlorophyll contents, antioxidant enzyme activity, and lipid peroxidation in rice seedlings exposed to Cr toxicity. The results showed that plant growth and chlorophyll content were dramatically reduced when rice plants were exposed to 100 μM Cr. Addition of GSH in the culture solution obviously alleviated the reduction of plant growth and chlorophyll content. The activities of some antioxidant enzymes, including superoxide dismutase, catalase (CAT) and glutathione reductase in leaves, and CAT and glutathione peroxidase in roots showed obvious increase under Cr stress. Addition of GSH reduced malondialdehyde accumulation and increased the activities of these antioxidant enzymes in both leaves and roots, suggesting that GSH may enhance antioxidant capacity in Cr-stressed plants. Furthermore, exogenous GSH caused significant decrease of Cr uptake and root-to-shoot transport in the Cr-stressed rice plants. It can be assumed that GSH is involved in Cr compartmentalization in root cells.     

Physiological and proteomic alterations in rice (Oryza sativa L.) seedlings under hexavalent chromium stress

Main Conclusion

Rice plants employ two strategies to cope with Cr toxicity: immobilizing Cr ions into cell walls to reduce its translocation and activating antioxidant defense to mitigate Cr-induced oxidative stress. The investigation aimed at understanding the physiological and proteomic responses of rice seedlings to hexavalent chromium (Cr⁶⁺) stress was conducted using two rice genotypes, which differ in Cr tolerance and accumulation. Cr toxicity (200 µM) heavily increased the accumulation of H₂O₂ and \({\text{O}}_{2}^{{ \cdot-}}\) , enhanced lipid peroxidation, decreased cell viability and consequently inhibited rice plant growth. Proteomic analyses suggest that the response of rice proteome to Cr stress is genotype- and Cr dosage-dependent and tissue specific. Sixty-four proteins, which show more than fourfold difference under either two Cr levels, have been successfully identified. They are involved in a range of cellular processes, including cell wall synthesis, energy production, primary metabolism, electron transport and detoxification. Two proteins related to cell wall structure, NAD-dependent epimerase/dehydratase and reversibly glycosylated polypeptide were greatly up-regulated by Cr stress. Their enhancements coupled with callose accumulation by Cr suggest that cell wall is an important barrier for rice plants to resist Cr stress. Some enzymes involved in antioxidant defense, such as ferredoxin-NADP reductase, NADP-isocitrate dehydrogenase, glyoxalase I (Gly I) and glutamine synthetase 1 (GS1) have also been identified in response to Cr stress. However, they were only detected in Cr-tolerant genotype, indicating the genotypic difference in the capacity of activating the defense system to fight against Cr-induced oxidative stress. Overall, two strategies in coping with Cr stress in rice plants can be hypothesized: (i) immobilizing Cr ions into cell walls to reduce its translocation and (ii) activating antioxidant defense to mitigate Cr-induced oxidative stress.     

Comparative study of alleviating effects of GSH, Se and Zn under combined contamination of cadmium and chromium in rice (Oryza sativa)

A hydroponic experiment was conducted to study the ameliorative effects of separate or combined application of exogenous glutathione (GSH), selenium (Se) and zinc (Zn) upon 20 μM cadmium (Cd) plus 20 μM chromium (Cr) heavy metal stress (HM) in rice seedlings. The results showed that HM caused a marked reduction in seedling height, chlorophyll content (SPAD) and biomass, and activities of catalase (CAT) and ascorbate peroxidase (APX) in leaves and H⁺-ATPase in roots/leaves, but elevated superoxide dismutase (SOD) and guaiacol peroxidase (POD) activities in leaves with elevated malondialdehyde (MDA) accumulation both in leaves and roots over the control. The best mitigation effect was recorded in HM+GSH+Zn and HM+GSH (addition of GSH+Zn and GSH to HM solution), which greatly alleviated HM-induced growth inhibition and oxidative stress. Compared with HM alone, HM+GSH and HM+GSH+Zn markedly reduced Cr uptake and translocation but not affected Cd concentration; improved H⁺-ATPase activity and Fe, Zn, Mn uptake and translocation, and repressed MDA accumulation. Meanwhile exogenous GSH and GSH+Zn counteracted HM-induced response of antioxidant enzymes, via suppressing HM-induced dramatic increase of root/leaf SOD and leaf POD activities, and elevating stress-depressed leaf APX and leaf/root CAT activities.