Feibo Wu

The influence of pH and organic matter content in paddy soil on heavy metal availability and their uptake by rice plants

The experiments were done to investigate the effect of soil pH and organic matter content on EDTA-extractable heavy metal contents in soils and heavy metal concentrations in rice straw and grains. EDTA-extractable Cr contents in soils and concentrations in rice tissues were negatively correlated with soil pH, but positively correlated with organic matter content. The combination of soil pH and organic matter content would produce the more precise regression models for estimation of EDTA-Cu, Pb and Zn contents in soils, demonstrating the distinct effect of the two factors on the availability of these heavy metals in soils. Soil pH greatly affected heavy metal concentrations in rice plants. Furthermore, inclusion of other soil properties in the stepwise regression analysis improved the regression models for predicting straw Fe and grain Zn concentrations, indicating that other soil properties should be taken into consideration for precise predicting of heavy metal concentrations in rice plants.

Four barley genotypes respond differently to cadmium: lipid peroxidation and activities of antioxidant capacity

A hydroponic experiment was carried out in a greenhouse to study genotypic differences in the effect of four Cd levels on lipid peroxidation and activities of antioxidant enzymes in barley plants during ontogenesis. A highly significant increase in malondialdehyde (MDA) content, and a stimulation of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were recorded in plants subjected to 1 and 5 μM Cd. The effects increased with both Cd concentration in the medium and with time of exposure in 5 μM Cd treatments. There was a highly significant difference in the alternation of all these parameters but CAT activity among the four genotypes. Wumaoliuling, which was relatively sensitive to Cd toxicity in terms of growth, biomass and chlorophyll content both in the previous and present studies, accumulated much more MDA when exposed to 5 μM Cd than the three other relatively tolerant genotypes (Zhenong 1, ZAU 3 and Mimai 114). In contrast, the three tolerant genotypes maintained higher SOD and POD activities than Wumaoliuling over the whole duration of Cd exposure. The present investigation showed that Cd-stress induced a concentration- and genotype-dependent oxidative stress response in barley leaves, characterized by an accumulation of MDA and the alternation pattern of antioxidative enzymes, mainly SOD and POD may be attributed to the genotypic difference in Cd tolerance.

Modulation of exogenous glutathione in antioxidant defense system against Cd stress in the two barley genotypes differing in Cd tolerance.

Soil cadmium (Cd) contamination has posed a serious problem for safe food production and become a potential agricultural and environmental hazard worldwide. Greenhouse hydroponic experiments were conducted to investigate the modulation of exogenous GSH (reduced glutathione) in antioxidant defense system against the Cd-induced toxicity in plants exposed to 5 muM Cd using two barley genotypes differing in Cd tolerance. Addition of 20 mg L(-1) GSH in 5 muM Cd culture medium significantly alleviated Cd-induced growth inhibition, especially for the sensitive genotype Dong 17 and dramatically depressed O(2)(-), H(2)O(2) and malondialdehyde (MDA) accumulation. GSH mediated intracellular GSH content to keep the level over the control especially in the case of Cd-induced GSH reduction. External GSH counteracted Cd-induced alterations of certain antioxidant enzymes, e.g. brought root dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione peroxidase (GPX) activities of the both genotypes down towards the control level, but elevated the depressed ascorbate peroxidase (APX) and catalase (CAT) activities in Dong 17 after 10-15 d treatment. The examination of APX and superoxide dismutase (SOD) isoenzymes revealed GSH significantly increased MnSOD, sAPX and tAPX activities in the both genotypes, and strongly stimulated Cd-induced decrease in cAPX in the sensitive genotype. Furthermore, External GSH up-regulated root cAPX and leaf cAPX, CAT1, and CAT2 expression at transcript level in Dong 17 to achieve stimulation. These data, especially from the results of depressed O(2)(-), H(2)O(2) and MDA accumulation and elevated Cd-induced decrease in GSH content and APX (strongly stimulated cAPX, sAPX and tAPX) and CAT activities by GSH addition in the sensitive genotype, suggest that elevated intracellular GSH and stimulated APX (especially cAPX, sAPX and tAPX iosenzymes) and CAT activities, when concerning ROS scavenging systems, play an important role in GSH-induced alleviation of oxidative stress.

Comparative Proteomic Analysis of Aluminum Tolerance in Tibetan Wild and Cultivated Barleys

Aluminum (Al) toxicity is a major limiting factor for plant production in acid soils. Wild barley germplasm is rich in genetic diversity and may provide elite genes for crop Al tolerance improvement. The hydroponic-experiments were performed to compare proteomic and transcriptional characteristics of two contrasting Tibetan wild barley genotypes Al- resistant/tolerant XZ16 and Al-sensitive XZ61 as well as Al-resistant cv. Dayton. Results showed that XZ16 had less Al uptake and translocation than XZ61 and Dayton under Al stress. Thirty-five Al-tolerance/resistance-associated proteins were identified and categorized mainly in metabolism, energy, cell growth/division, protein biosynthesis, protein destination/storage, transporter, signal transduction, disease/defense, etc. Among them, 30 were mapped on barley genome, with 16 proteins being exclusively up-regulated by Al stress in XZ16, including 4 proteins (S-adenosylmethionine-synthase 3, ATP synthase beta subunit, triosephosphate isomerase, Bp2A) specifically expressed in XZ16 but not Dayton. The findings highlighted the significance of specific-proteins associated with Al tolerance, and verified Tibetan wild barley as a novel genetic resource for Al tolerance.

Tissue Metabolic Responses to Salt Stress in Wild and Cultivated Barley

A thorough understanding of the mechanisms underlying barley salt tolerance and exploitation of elite genetic resource are essential for utilizing wild barley germplasm in developing barley varieties with salt tolerance. In order to reveal the physiological and molecular difference in salt tolerance between Tibetan wild barley (Hordeum spontaneum) and cultivated barley (Hordeum vulgare), profiles of 82 key metabolites were studies in wild and cultivated barley in response to salinity. According to shoot dry biomass under salt stress, XZ16 is a fast growing and salt tolerant wild barley. The results of metabolite profiling analysis suggested osmotic adjustment was a basic mechanism, and polyols played important roles in developing salt tolerance only in roots, and high level of sugars and energy in roots and active photosynthesis in leaves were important for barley to develop salt tolerance. The metabolites involved in tolerance enhancement differed between roots and shoots, and also between genotypes. Tibetan wild barley, XZ16 had higher chlorophyll content and higher contents of compatible solutes than CM72, while the cultivated barley, CM72 probably enhanced its salt tolerance mainly through increasing glycolysis and energy consumption, when the plants were exposed to high salinity. The current research extends our understanding of the mechanisms involved in barley salt tolerance and provides possible utilization of Tibetan wild barley in developing barley cultivars with salt tolerance.

Selenium reduces cadmium uptake and mitigates cadmium toxicity in rice

Hydroponic experiments were performed to investigate physiological mechanisms of selenium (Se) mitigation of Cd toxicity in rice. Exogenous Se markedly reduced Cd concentration in leaves, roots, and stems. Addition or pretreatment of 3 μM Se in 50 μM Cd solution significantly addressed Cd-induced growth inhibition, recovered root cell viability, and dramatically depressed O(2)(-), H(2)O(2), and malondialdehyde (MDA) accumulation. Supplemental Se counteracted 50 μM Cd-induced alterations of certain antioxidant enzymes, and uptake of nutrients, e.g. depressed Cd-induced increase in leaf and root superoxide dismutase (SOD) and leaf peroxidase (POD) activities, but elevated depressed catalase (CAT) activity; decreased Cd-induced high S and Cu concentrations in both leaves and roots. External Se counteracted the pattern of alterations in ATPase activities induced by Cd, e.g. significantly elevated the depressed root H(+)- and Ca(2+)-ATPase activities, but decreased the ascent root Na(+)K(+)-ATP activity. Results indicate that alleviated Cd toxicity by Se application is related to reduced Cd uptake and ROS accumulation, balanced nutrients, and increased H(+)- and Ca(2+)-ATPase activities in rice.

Genotypic differences in physiological characteristics in the tolerance to drought and salinity combined stress between Tibetan wild and cultivated barley

Greenhouse pot experiments were conducted to investigate genotypic differences in response to individual and combined stresses of drought and salinity between Tibetan wild barley genotypes (XZ5, drought-tolerant; XZ16, salinity/aluminum tolerant) and cv. CM72 (salinity-tolerant). Either drought (D) or salinity (S) alone and in combination (D + S) stresses significantly decreased plant growth, chlorophyll content, net photosynthetic rate (Pn), maximal photochemical efficiency of PSII (Fv/Fm), water potential and osmotic potential, with the largest suppression under combined stress, and two wild genotypes showing more tolerance than CM72. Water use efficiency (WUE) increased significantly in XZ5 and XZ16 after D + S, but no significant change in CM72. XZ5 and XZ16 showed 30.9% and 12.1% higher K(+) level and 30.5% and 24.1% lower Na(+)/K(+) ratio in plants, compared with CM72, with increased metal nutrients as Ca, Fe and Mn under D + S. The peak accumulation in proline and glycine-beatine was recorded in combined stress with larger accumulation in two wild genotypes. Moreover, larger increases in the level of ASA and GSH, and the activities of Ca(2+)Mg(2+)-ATPase, and superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), guaiacol peroxidase (POD) and glutathione reductase (GR) under D + S vs control were observed in XZ5 and XZ16 than CM72, with less accumulation of H(2)O(2) and malondialdehyde. These results suggest that high tolerance to D + S stress of XZ5 and XZ16 is closely related to lower Na(+)/K(+) ratio and enhanced Ca(2+)Mg(2+)-ATPase, proline, glycine-beatine and WUE, and improved capacity of antioxidative performance to scavenge reactive oxygen species and thus suppressed level of lipid peroxidation.

Evaluation of salinity tolerance and analysis of allelic function of HvHKT1 and HvHKT2 in Tibetan wild barley

Tibetan wild barley is rich in genetic diversity with potential allelic variation useful for salinity-tolerant improvement of the crop. The objectives of this study were to evaluate salinity tolerance and analysis of the allelic function of HvHKT1 and HvHKT2 in Tibetan wild barley. Salinity tolerance of 189 Tibetan wild barley accessions was evaluated in terms of reduced dry biomass under salinity stress. In addition, Na+ and K+ concentrations of 48 representative accessions differing in salinity tolerance were determined. Furthermore, the allelic and functional diversity of HvHKT1 and HvHKT2 was determined by association analysis as well as gene expression assay. There was a wide variation among wild barley genotypes in salt tolerance, with some accessions being higher in tolerance than cultivated barley CM 72, and salinity tolerance was significantly associated with K+/Na+ ratio. Association analysis revealed that HvHKT1 and HvHKT2 mainly control Na+ and K+ transporting under salinity stress, respectively, which was validated by further analysis of gene expression. The present results indicated that Tibetan wild barley offers elite alleles of HvHKT1 and HvHKT2 conferring salinity tolerance.

Alleviation of aluminum toxicity by hydrogen sulfide is related to elevated ATPase, and suppressed aluminum uptake and oxidative stress in barley.

Greenhouse hydroponic experiments were performed to evaluate potential role of H(2)S on Al toxicity in barley seedlings. Seedlings pretreated with 200 μM NaHS as a donor of H(2)S for 24h and subsequently exposed to 100 μM AlCl(3) for 24h had significantly longer roots than those without NaHS. The promoted root elongation was correlated with a substantial decrease in Al-induced overproduction of lipid peroxidation, electrolyte leakage and Al accumulation in roots, and a marked increase in Al-induced depress activities of Na(+)K(+)-ATPase and H(+)-ATPase. The alleviating role of H(2)S on Al-induced toxicity was also found in a time- and dose-dependent experiment. Addition of 200 and 400 μM NaHS to 100 μM AlCl(3) effectively alleviated Al-toxicity, markedly diminished Al-induced MDA accumulation, and increased chlorophyll content, net photosynthetic rate (Pn) and maximal photochemical efficiency (Fv/Fm) compared with Al alone. Exogenous H(2)S significantly elevated depressed CAT activities, and further improved root POD activity. Moreover, NaHS decreased Al accumulation, but elevated concentrations of S, P, Ca, Mg and Fe in plants. These data suggest that H(2)S-induced alleviation in Al toxicity is attributed to reduced Al uptake and MDA accumulation, improved uptake of P, Ca, Mg and Fe, and elevated ATPase and photosynthetic performance.

Comparative proteomic analysis of Typha angustifolia leaf under chromium, cadmium and lead stress

The present study investigated Typha angustifolia leaf proteome in response to Cr, Cd and Pb stress. T. angustifolia of 90 (D90) and 130d (D130) old plants were subjected to 1mM Cr, Cd and Pb and samples were collected 30d after treatment. 2-DE coupled with MS (mass spectrometry) was used to analyze and identify Cr, Cd and Pb-responsive proteins. More than 1600 protein spots were reproducibly detected on each gel, wherein 44, 46, 66 and 33, 26, 62 spots in D90 and D130 samples were differentially expressed by Cr, Cd, Pb over the control, respectively. Of these differentially expressed proteins, 3, 1, 8 overlapped in D90 and D130; while 5, 8, 5 with regulation factors above 3 in one of D90 or D130 samples. Total of 22 and 4 up- and down-regulated proteins were identified using MS and data bank analysis. Cr-induced expression of ATP synthase, RuBisCO small subunit and coproporphyrinogen III oxidase; Cd-induced RuBisCO large subunit; Pb up-regulated carbohydrate metabolic pathway enzymes of fructokinase, and improved RuBisCO activase and large subunit, Mg-protoporphyrin IX chelatase. Contrarily, elF4F was inhibited by Cr/Pb, chloroplast FtsZ-like protein and GF14 omega impeded by Cd and Pb, respectively.