| Sulfur (S) is an essential macronutrient for plant growth and development. Sulfur deficiency reduces crop yield and affects the quality of harvested products. Sulfur deficiency is increasing seriously over the past two decades worldwide, mainly because of the reduction of sulfur dioxide emission from power plants and various industrial sources, increasing use of low-S-containing fertilizers and decreasing use of S-containing fungicides and pesticides. In addition, intensive agriculture is facing low yields, poor quality of products and inadequacy of crop plants to cope with environmental hazards. Barley is an important cereal crop grown mainly for feed, malt and food. Sulfur deficiency may also have impacts on growth and quality of barley. The central theme of this study was to investigate the role of S on barley growth, nutrient uptake capacity and grain quality. Moreover, ameliorating affects of hydrogen sulfide (H2S, a sulfur containing defense compound) on aluminum (Al), cadmium (Cd) and salinity stresses in barley were also examined. A series of experiments were performed and the following useful findings were achieved.1. Alleviation effects of exogenous H2S on Al toxicity in barleyGreenhouse hydroponic experiments were performed to evaluate potential role of H2S on Al toxicity in barley seedlings. Seedlings pretreated with200μM NaHS as a donor of H2S for24h and subsequently exposed to100μM AICl3for24h 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 H2S on Al-induced toxicity was also found in a time-and dose dependent experiment. Addition of200and400uM NaHS to100μM AICl3effectively 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 H2S 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 H2S-induced alleviation in Al toxicity is attributed to reduced A1uptake and MDA accumulation, improved uptake of P, Ca, Mg and Fe, and elevated ATPase and photosynthetic performance.2. Effect of exogenous H2S on growth, photosynthesis and antioxidative capacity of barley plants under cadmium stressEffect of exogenous H2S on Cd toxicity in barley was studied through a long term (25and40d) hydroponic experiment. Seedlings exposed to5and25μM Cd markedly reduced plant height, root length and biomass. Addition of200μM NaHS (as H2S-donor) to5or25μM Cd (Cd5+S or Cd25+S) significantly alleviated Cd-toxicity, and markedly increased plant height, root length, shoot biomass by24%,26%,43%in Cd5+S compared with5μM Cd alone, and by29%,24%,118%in Cd25+S over25μM Cd, respectively, after40d exposure. H2S-based increased tolerance was associated with decrease in MDA contents, increase in Cd-suppressed SOD in leaves and roots and POD activity in roots, Moreover, improved photosynthesis with improved chlorophyll content, photosynthetic rate (Pn) and stomatal conductance (Gs) parameters were also characteristics of exogenous application of H2S. Addition of H2S also reduced Cd concentrations in roots, stems and leaves, i.e. inhibited Cd uptake and further declined its translocation from roots to aboveground portions.3. Effect of exogenous hydrogen sulfide on growth, photo synthesis and antioxidative system of barley under salinity stressGreen house hydroponic experiment was performed to evaluate the potential alleviation of exogenous H2S on salinity stress in barley. Plants grown in100mM NaCl were showed severe reduction in plant height, root length and shoot and root dry biomass. Exogenous H2S (NaCl+S, addition of200μM NaHS in100mM NaCl solution) significantly alleviated salt stress induced growth inhibition, yielding14%and12%increase in plant height and shoot dry weight as compared with NaCl alone. H2S significantly reduced Na+accumulation in stems, elevated K+in roots and resulted in significant lower Na+/K+ratio, especially in roots. HhS-mediated salinity alleviation was correlated with decline in MDA content, and elevation of salinity-depressed SOD, CAT and APX activities in roots and POD in leaves and roots. Exogenous H2S also improved photosynthesis with significant increase in stomatal conductance and net photosynthetic rate. It was deduced that H2S is an excellent candidate for salinity tolerance in barley, which lowered oxidative stress, enhanced antioxidative system, catalyzed K+entry into roots, improved photosynthesis and yielded91%tolerance index compared with76%of salinity alone treatment, after40days exposure.4. Effect of sulfur nutrition on growth, nutrient uptake and grain composition of barleyGrowth and yield responses of two hydroponically grown barley cultivars (Gairdner and ZD-9) to various sulfur (S) levels were studied via evaluating nutrient status of different plant tissues, grain composition and yield components. S-deprivation resulted in reduced plant heights and biomass at maturity decreased chlorophyll content in flag leaves at anthesis. Gairdner was more sensitive to S deficiency than ZD-9in terms of yield components, i.e. compared with normal S level, SO (no sulfur) induced much more reduction in spikes per plant, grains per spike and thousand grain weight (TGW) in Gairdner than that in ZD-9. At anthesis, S-deficient plants had lower S concentration in flag leaves, shoots, spikes and roots of both cultivars over the normal S treatment. S-deprivation (S0, no sulfur) reduced P concentration in flag leaves and shoots of ZD-9and accumulated more P in roots of both cultivars. S-free grown medium severely declined Ca and Zn concentration in mature grains of both cultivars, and P, Mg and B in ZD-9. The highest grain N and protein concentrations were recorded in SO.5applied solution in ZD-9(being15%and10%higher than that in SO and S2.0), while in S1.0and S2.0in Gairdner (being21%and30%higher than that in SO). The lowest N:S ratio was found in S1.0and S2.0treatments of both cultivars with ZD-9lower than Gairdner. Rational S fertilization was found effective, especially in ZD-9in maintaining growth, improving nutrient status of plant tissues and lowering undesirable higher-N:S (malting purpose) ratio in grains.5. Proteome and amino acid profile in mature barley grains as affected by sulfur fertilizationMature barley grains of two cultivars, grown hydroponically with0,1.0and2.0mM sulfur were analyzed for identification of S-responsive proteins through2-DE coupled with MS (mass spectrometry). More than1500spots were reproducibly detected on each gel. Overall,58and73protein spots were found to be altered by S-deprivation in ZD-9and Gairdner over the control, respectively. Total of26proteins were identified using MS and data bank analysis, out of which12,10and6proteins were suppressed in S-deprivation treatment relative to normal-S in Gairdner and ZD-9, respectively; while6proteins were suppressed in both cultivars. Sulfur starvation depressed Beta-Amy1, Alpha-amylase flour inhibitor, beta-amylase, cytosolic glutamine synthetase alpha and embryo globulin in both cultivars. Putative serine threonine kinase, trypsin inhibitor cme precursor and z-type serpin were down-regulated by SO over control in ZD-9only. Similarly, N-rich amino acids like arginine, lysine, proline and glycine were increased in S-deficient grains, while S-containing Cys and Met were decreased. |
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