Boyin Qiu

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.

Alleviation of Chromium Toxicity by Silicon Addition in Rice Plants

Abstract The alleviatory effect of silicon (Si) on chromium (Cr) toxicity to rice plants was investigated using a hydroponic experiment with two Cr levels (0 and 100 μmol L −1 ), three Si levels (0, 1.25, and 2.5 mmol L −1 ) and two rice genotypes, differing in grain Cr accumulation (Dan K5, high accumulation and Xiushui 113, low accumulation). The results showed that 100 μmol L −1 Cr treatment caused a marked reduction of seedling height, dry biomass, soluble protein content, and root antioxidant enzyme activity, whereas significantly increased Cr concentration and TBARS (thiobarbituric acid reactive substances) content. However, the reductions of seedling height, dry biomass, and soluble content were greatly alleviated due to Si addition to the culture solution. Compared with the plants treated with Cr alone, Si addition markedly reduced Cr uptake and translocation in rice plants. No significant differences were observed between the two Si treatments (1.25 and 2.5 mmol L −1 ) in shoot Cr concentration and Cr translocation factor. Under the treatment of 100 μmol L −1 Cr+2.5 mmol L −1 Si, higher root Cr concentration but lower shoot Cr concentration and Cr translocation factor were observed in Dan K5 than those in Xiushui 113, indicating that the beneficial effect of Si on inhibiting Cr translocation was more pronounced in Dan K5 than in Xiushui 113. Si addition also alleviated the reduction of antioxidative enzymes (superoxide dismutase (SOD) and ascorbate peroxidase (APX) in leaves; catalase (CAT) and APX in roots) and the increase of TBARS content in the Cr-stressed plants. Furthermore, the beneficial effects of Si on activities of antioxidative enzymes under Cr stress were genotype-dependent. The highest activities of SOD, POD (guaiacol peroxidase), CAT, and APX in leaves occurred in the treatment of 100 μmol L −1 Cr+2.5 mmol L −1 Si for Xiushui 113 and in the treatment of 100 μmol L −1 Cr+1.25 mmol L −1 Si for Dan K5. The beneficial effect of Si on alleviating oxidative stress was much more pronounced in Dan K5 than in Xiushui 113. It may be concluded that Si alleviates Cr toxicity mainly through inhibiting the uptake and translocation of Cr and enhancing the capacity of defense against oxidative stress induced by Cr toxicity.

Alleviation of chromium toxicity in rice seedlings by applying exogenous glutathione

The effect of exogenous reduced glutathione (GSH) on alleviation of hexavalent chromium (Cr(6+)) toxicity to rice seedlings and its physiological mechanisms were comprehensively investigated in a series of experiments. Our results showed that growth and nutrient uptake of rice seedlings were dramatically reduced under 100 μM Cr(6+) stress, and the reduction was significantly alleviated by exogenous GSH. Cr(6+) stress also reduced cell viability in root tips and damaged ultrastructure of both chloroplasts and root cells, while the addition of GSH alleviates those negative effects. Cr-induced toxicity and GSH-caused Cr alleviation differed significantly between Cr-tolerant Line 117 (L117) and Cr-sensitive Line 41 (L41). Under Cr(6+) stress, cystine content was increased and GSH content was decreased in rice plants, exogenous GSH, however, mitigated the Cr-toxicity by reversing the Cr-induced changes of the two compounds. The types of Cr-induced secretion of organic acids varied between the genotypes, where reduction in the contents of acetic and lactic acids and tartaric and malic acids were observed in L117 and L41, respectively. The addition of GSH alleviated the reduction of secretion of these organic acids. Exogenous GSH also altered the forms of Cr ions in the rhizosphere and the fraction of distribution at subcellular level in both shoots and roots. It may be concluded that the alleviation of Cr(6+) toxicity by exogenous GSH is directly attributed to its regulation on forms of Cr ions in rhizosphere and their distribution at subcellular levels.

Genotypic differences in nutrient uptake and accumulation in rice under chromium stress.

The effect of chromium (Cr) on the uptake, distribution and accumulation of nine nutrient elements was studied in two rice genotypes, Xiushui 113 and Dan K5. The effect on elemental concentrations and accumulations varied with Cr level, nutrient element, genotype and plant part. Maximum nutrient accumulation occurred at 10 μM Cr, while the minimum occurred at 100 μM Cr, indicating best plant growth at the 10 μM level. It may be assumed that low Cr level enhance plant growth. The correlation between the concentrations of Cr and nine elements differed among plant parts, but Cr accumulation was significantly and negatively correlated with the accumulation of each element, suggesting that increasing Cr level may create nutrient deficiencies or imbalance in rice.

EFFECT OF SALINITY AND HEXAVALENT CHROMIUM STRESSES ON UPTAKE AND ACCUMULATION OF MINERAL ELEMENTS IN BARLEY GENOTYPES DIFFERING IN SALT TOLERANCE

The effect of hexavalent chromium (Cr) and sodium chloride (NaCl) stresses on the uptake and accumulation of mineral nutrients in two barley (Hordeum vulgare L.) genotypes differing in salt tolerance was investigated in this study. Sodium chloride stress decreased potassium (K), magnesium (Mg), calcium (Ca), iron (Fe), zinc (Zn), manganese (Mn) and copper (Cu) concentration and accumulation in barley plants, and there was less of a decrease in salt-tolerant ‘CM72’, than in ‘Gairdner’, a salt-sensitive genotype. The effect of Cr on mineral concentration and accumulation varied with Cr level. At a high Cr level (50 μM), concentration and accumulation of all mineral elements were significantly reduced. But at a low Cr level (10 μM), nutrient concentration and accumulation were increased. Moreover, low Cr level alleviated the inhibiting effect of NaCl stress on nutrient uptake and accumulation. The combined stress of high Cr level and NaCl stress, on the whole caused further reduction of the mineral concentration and accumulation as compared to two stresses alone.

Interactive effects of aluminum and chromium stresses on the uptake of nutrients and the metals in barley

Aluminum (Al) and chromium (Cr) stresses often occur simultaneously in agricultural soils, and pose a great damage to crop growth, yield formation and product safety. In the current study, the influence of combined Al and Cr stresses on plant biomass, metal and nutrient contents was determined in comparison with that of Al or Cr stress alone. A hydroponic experiment was conducted to investigate the effect of pH, Al and Cr in the medium solution on the uptake of mineral elements as well as Al and Cr in the two barley genotypes differing in Al tolerance. Aluminum sensitive genotype Shang 70-119 had significantly higher Cr and Al contents in plants than Al-tolerant genotype Gebeina. Barley roots had much higher Al and Cr contents than above-ground plant parts. Chromium contents were much higher in the solution with pH 4.0 than in that with pH 6.5. Aluminum stress reduced phosphorus (P), calcium (Ca), magnesium (Mg), sulfur (S), copper (Cu), manganese (Mn), zinc (Zn) and boron (B) contents in roots and restrained potassium (K) and iron (Fe) from being translocated into shoots and leaves. Chromium stress resulted in reduced P, K, Mg, S, Fe, Zn and Mn contents in roots at pH 6.5 and P, K, Ca, Mg, S, Zn and Mn contents at pH 4.0. Translocation of all nutrients from roots to upper parts of plants was inhibited except Ca in pH 6.5 with Cr addition. Lower contents of all nutrients were observed at pH 4.0 as compared to pH 6.5. Combined stress of Cr and Al, on the whole, caused further reduction in mineral content in all plant parts of the two barley genotypes as compared to Al or Cr stress alone. Moreover, the reduction was more pronounced in Al sensitive genotype Shang 70-119.

Differences in Phytase Activity and Phytic Acid Content between Cultivated and Tibetan Annual Wild Barleys

The Qinghai-Tibetan Plateau in China is considered to be one of the original centers of cultivated barley. At present, little is known about the phytase activity (Phy) or phytic acid content (PA) in grains of Tibetan annual wild barley. Phy and PA were determined in grains of 135 wild and 72 cultivated barleys. Phy ranged from 171.3 to 1299.2 U kg(-1) and from 219.9 to 998.2 U kg(-1) for wild and cultivated barleys, respectively. PA and protein contents were much higher in wild barley than in cultivated barley. Tibetan annual wild barley showed a larger genetic diversity in phytase activity and phytic acid and protein contents and is of value for barley breeding. There is no significant correlation between phytase activity and phytic acid or protein content in barley grains, indicating that endogenous phytase activity had little effect on the accumulation of phytic acid.

The effect of H2O2 and abscisic acid (ABA) interaction on β-amylase activity under osmotic stress during grain development in barley

The effects of exogenous abscisic acid (ABA) and polyethylene glycol (PEG 6000) treatments on grain H(2)O(2), ABA and beta-amylase activity were studied during grain development in the spike culture experiments with variety Triumph and its ABA-insensitive mutant TL43 as the plant materials. The results showed that during grain development the two genotypes were similar in the pattern of ABA concentration change, but differed greatly in the pattern of H(2)O(2) concentration and beta-amylase activity changes. The beta-amylase activity was positively correlated with H(2)O(2) concentration, negatively correlated with ABA concentration, and it is mainly closely associated with continued high levels of ABA with respect to H(2)O(2). Water stress (PEG treatment) induced beta-amylase was associated with H(2)O(2) concentration but not with ABA concentration. Exogenous application of H(2)O(2) and Ascorbic acid (AsA) increased beta-amylase activity in Triumph but reduced that of TL43. However, the endogenous H(2)O(2) concentration in grains was always consistent with beta-amylase activity. A novel model was hypothesized from the current results to illustrate the relationship between H(2)O(2), ABA and beta-amylase synthesis for the barley exposed to abiotic stresses.

Identification of Cr-tolerant lines in a rice (Oryza sativa) DH population

Identification of Cr-tolerant lines in a rice DH population was conducted based on the modified weighted function analysis. The significant difference was found between the two parents and among DH population lines, with lines 117, 101 and parent ZYQ8 showing the high Cr tolerance, lines 41 and 49 showing Cr sensitivity. A dramatic difference also existed in Cr accumulation of plant tissues, with lines 19, 18 and 1, 5 having the minimum and maximum shoot Cr accumulation, respectively, and line 19, parent JX17 and lines 1, 56, ZYQ8 having the minimum and maximum root Cr accumulation, respectively. There was a significant difference in shoot/root ratio of Cr accumulation among the population, with line 18 and parent ZYQ8 ranking the tops and lines 109, 71, 19, parent JX17 ranking the bottoms. Zn uptake and accumulation was reduced when the plants were exposed to Cr stress. In addition, three QTLs were detected, which are, respectively, associated with Cr accumulation in shoot and root, and ratio of shoot to root.

QTL mapping for chromium-induced growth and zinc, and chromium distribution in seedlings of a rice DH population

Chromium contamination in soil has become a severe threat to crop production and food safety. The experiment was conducted using a rice DH population to detect the QTLs associated with Cr tolerance. Seventeen putative QTLs associated with growth traits included three additive loci and fourteen epistatic loci. These loci were distributed on 11 rice chromosomes, and their contribution to the phenotypic variation ranged from 2.44 to 10.08%. Two QTLs located at the similar genetic region on chromosome ten were associated with shoot Cr concentration and translocation from roots to shoots, respectively; and they accounted for 11.65 and 11.22% of the phenotypic variation. In addition, six QTLs related to Zn concentration and translocation was found on chromosomes 1, 2, 4, 5, 7 and 12. Meanwhile epistatic effect existed in the two additive QTLs of qRZC1 and qRZC7. Most of QTLs controlling Zn concentration had small genotypic variance and qSRZ4 related to Zn translocation showed growth condition-dependent expression.