Fangbin Cao

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.

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.

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.

Difference in Yield and Physiological Features in Response to Drought and Salinity Combined Stress during Anthesis in Tibetan Wild and Cultivated Barleys

Soil salinity and drought are the two most common and frequently co-occurring abiotic stresses constraining crop growth and productivity. Greenhouse pot experiments were conducted to investigate the tolerance potential and mechanisms of Tibetan wild barley genotypes (XZ5, drought-tolerant; XZ16, salinity/aluminum tolerant) during anthesis compared with salinity-tolerant cv CM72 in response to separate and combined stresses (D+S) of drought (4% soil moisture, D) and salinity (S). Under salinity stress alone, plants had higher Na+ concentrations in leaves than in roots and stems. Importantly, XZ5 and XZ16 had substantially increased leaf K+ concentrations; XZ16 was more efficient in restricting Na+ loading in leaf and maintained a lower leaf Na+/K+ ratio. Moreover, a significant decrease in cell membrane stability index (CMSI) and an increase in malondialdehyde (MDA) were accompanied by a dramatic decrease in total biomass under D+S treatment. We demonstrated that glycine-betaine and soluble sugars increased significantly in XZ5 and XZ16 under all stress conditions, along with increases in protease activity and soluble protein contents. Significant increases were seen in reduced ascorbate (ASA) and reduced glutathione (GSH) contents, and in activities of H+K+-, Na+K+-, Ca++Mg++-, total- ATPase, and antioxidant enzymes under D+S treatment in XZ5 and XZ16 compared to CM72. Compared with control, all stress treatments significantly reduced grain yield and 1000-grain weight; however, XZ5 and XZ16 were less affected than CM72. Our results suggest that high tolerance to D+S stress in XZ5 and XZ16 is closely related to the lower Na+/K+ ratio, and enhanced glycine-betaine and soluble protein and sugar contents, improved protease, ATPase activities and antioxidative capacity for scavenging reactive oxygen species during anthesis. These results may provide novel insight into the potential responses associated with increasing D+S stress in wild barley genotypes.

Genotypic dependent effect of exogenous glutathione on Cd-induced changes in proteins, ultrastructure and antioxidant defense enzymes in rice seedlings

Greenhouse hydroponic experiments were conducted using Cd-sensitive (cv. Xiushui63) and tolerant (Bing97252) rice genotypes to evaluate how different genotypes responded to Cd toxicity in presence of glutathione (GSH). Results showed that GSH alleviates Cd-toxicity, ameliorates Cd-induced damages on leaf/root ultrastructures. Nine proteins in roots were identified, using 2-DE coupled with mass spectrometry, whose expression were down-regulated in Xiushui63, up-regulated/unchanged in Bing97252 by Cd; coinstantaneously enhanced/unchanged in Cd+GSH over Cd alone treatment in both genotypes. They are l-ascorbate peroxidase, putative short-chain dehydrogenase/reductase, Glycolipid transfer protein, elongation factor, Os04g0652700, carbonic anhydrase, Os08g0374000, chitinase, and putative disease resistance response protein. Eight proteins in leaves with expression of increase in Bing97252 but down-regulate/unchange in Xiushui63, categorized as four groups of their functions: carbon metabolism, TCA cycle, photorespiration and RNA processing. Furthermore, we identified eight proteins with repressed expression in Cd-treated and up-regulated in Cd+GSH-treated rice leaves of Xiushui63.

Genome-wide transcriptome and functional analysis of two contrasting genotypes reveals key genes for cadmium tolerance in barley.

BackgroundCadmium (Cd) is a severe detrimental environmental pollutant. To adapt to Cd-induced deleterious effects, plants have evolved sophisticated defence mechanisms. In this study, a genome-wide transcriptome analysis was performed to identify the mechanisms of Cd tolerance using two barley genotypes with distinct Cd tolerance.ResultsMicroarray expression profiling revealed that 91 genes were up-regulated by Cd in Cd-tolerant genotype Weisuobuzhi and simultaneously down-regulated or non-changed in Cd-sensitive Dong17, and 692 genes showed no change in Weisuobuzhi but down-regulated in Dong17. Novel genes that may play significant roles in Cd tolerance were mainly via generating protectants such as catalase against reactive oxygen species, Cd compartmentalization (e.g. phytochelatin-synthase and vacuolar ATPase), and defence response and DNA replication (e.g. chitinase and histones). Other 156 up-regulated genes in both genotypes also included those encoding proteins related to stress and defence responses, and metabolism-related genes involved in detoxification pathways. Meanwhile, biochemical and physiological analysis of enzyme (ATPase and chitinase), phytohormone (ethylene), ion distribution and transport (Cd, Na+, K+, Ca2+, ABC transporter) demonstrated that significantly larger Cd-induced increases of those components in Weisuobuzhi than those in Dong17. In addition, Cd-induced DNA damage was more pronounced in Dong17 than that in Weisuobuzhi.ConclusionsOur findings suggest that combining microarray, physiological and biochemical analysis has provided valuable insights towards a novel integrated molecular mechanism of Cd tolerance in barley. The higher expression genes in Cd tolerant genotype could be used for transgenic overexpression in sensitive genotypes of barley or other cereal crops for elevating tolerance to Cd stress.

Genotypic and environmental variation in cadmium, chromium, lead and copper in rice and approaches for reducing the accumulation

The field scale trials revealed significant genotypic and environmental differences in grain heavy metal (HM) concentrations of 158 newly developed rice varieties grown in twelve locations of Zhejiang province of China. Grain Pb and Cd contents in 5.3% and 0.4% samples, respectively, were above the maximum permissible concentration (MPC); none of samples had Cr/Cu exceeding MPC. Stepwise multiple linear regression analysis estimated soil HM critical levels for safe rice production. Low grain HM accumulation cultivars such as Xiushui817, Jiayou08-1 and Chunyou689 were recommended as suitable cultivars for planting in slight/medium HM contaminated soils. The alleviating regulator (AR) of (NH₄)₂SO₄ as N fertilizer coupled with foliar spray of a mixture containing glutathione (GSH), Si, Zn and Se significantly decreased grain Cd, Cr, Cu and Pb concentrations grown in HM contaminated fields with no effect on yield, indicating a promising measurement for further reducing grain HM content to guarantee safe food production.

HvEXPB7, a novel β-expansin gene revealed by the root hair transcriptome of Tibetan wild barley, improves root hair growth under drought stress

Highlight A novel root hair development related gene, HvEXPB7, was identified and cloned from the identified drought tolerance-associated genes. BSMV-VIGS of HvEXPB7 confirmed that this gene was involved in root hair growth under drought.

Differential changes in grain ultrastructure, amylase, protein and amino acid profiles between Tibetan wild and cultivated barleys under drought and salinity alone and combined stress

Grain phytochemical profiles were compared in Tibetan wild barley XZ5 (drought-tolerant), XZ16 (salinity/aluminum-tolerant) and cv CM72 (salinity-tolerant) in response to drought and salinity alone and combination (D+S) during anthesis. Total antioxidant capacity assessed by determining ferric-reducing antioxidant potential (FRAP) in grains increased significantly as follows: D+S>drought>salinity, and XZ5>XZ16>CM72. A marked increase in the total phenol (TP) from individual and combined stresses was observed in XZ5, while a decrease occurred in CM72. Moreover, the activity of α-/β-amylase in the grains under combined stress was 81.8%/16.9% in XZ5 and 48.6%/18.7% in XZ16 higher than that of CM72. Increases in amino acids, protein content and protein fractions of albumin, globulin, hordein and glutelin were maximised under D+S, with larger values in the Tibetan wild genotypes. Observation with a scanning electron microscopy showed a distinct genotypic difference under D+S; for example, XZ5 and XZ16 maintained a relatively integral starch granule with a greater protein deposit/matrix, while CM72 degraded by pitting. This research expands our understanding of barley drought and salt-tolerance mechanisms and provides possibility of Tibetan wild barley in developing barley cultivars with both tolerance to drought and salinity.