[Effects of Exogenous Melatonin Treatment on the Growth and Antioxidant System of Rice Seedlings Under Antimony Stress].

To investigate the effect of exogenous application of melatonin (MT) on rice seedlings under antimony (Sb) stress, hydroponic experiments were carried out with rice seedlings (Huarun No.2). The fluorescent probe localization technology was used to locate the reactive oxygen species (ROS) in the root tips of rice seedlings, and the root viability, malondialdehyde (MDA) content, ROS (H2O2 and O2-·) content, antioxidant enzyme (SOD, POD, CAT, and APX) activities, and antioxidant (GSH, GSSG, AsA, and DHA) contents in the roots of rice seedlings were analyzed. The results showed that exogenous addition of MT could alleviate the adverse effects of Sb stress on the growth and increase the biomass of rice seedlings. Compared with the Sb treatment, the application of 100 µmol·L-1 MT increased rice root viability and total root length by 44.1% and 34.7% and reduced the content of MDA, H2O2, and O2-· by 30.0%, 32.7%, and 40.5%, respectively. Further, the MT treatment increased the activities of POD and CAT by 54.1% and 21.8%, respectively, and also regulated the AsA-GSH cycle. This research indicated that exogenous application of 100 µmol·L-1MT can promote the growth and antioxidant ability of rice seedlings and alleviate the damage of lipid peroxidation by Sb stress, thus improving the resistance of rice seedlings under Sb stress.

[Effects of Exogenous Jasmonic Acid on Arsenic Accumulation and Response to Stress in Roots of Rice Seedlings].

Arsenic (As) pollution has a toxic effect on crop growth, leading to reduced crop quality and yield. Therefore, it is urgent to explore safe and effective strategies to reduce its toxicity. In this experiment, hydroponics, fluorescent probe locating technology, differential centrifugation, and Fourier infrared spectroscopy (FTIR) analysis were used to research the effect of exogenous jasmonic acid (JA) on the accumulation and stress resistance of rice seedlings. The results showed that JA application reduced the As content in the roots and shoots of rice by 31.4% and 51.4%, respectively, and significantly reduced As content in the cell wall and soluble fractions of rice roots. JA changed the distribution ratio of As in the subcellular components. The distribution ratio of As in the cell wall increased by 16.4%, and the distribution ratio of soluble fractions decreased by 17.3%. JA enhanced the fixation of As by the cell wall and reduced the As content in the soluble fraction. Furthermore, JA increased the levels of SOD, CAT, GSH, and PEPC in root cells and reduced the contents of H2O2 and MDA, indicating that JA reduced lipid peroxidation damage, regulated carbon and nitrogen metabolism, and alleviated As toxicity. This research provides a new approach for the prevention and control of rice As pollution.

[Effect of Chelating Agents and Organic Acids on Remediation of Cadmium and Arsenic Complex Contaminated Soil Using Xanthium sibiricum].

In order to improve the phytoextraction efficiency of Xanthium sibiricum on farmland soil that had been contaminated by Cd and As, this study explored the effects of chelating agents and organic acids (EDTA, SAP, CA, and MA) on the extraction of Cd and As heavy metals using X. sibiricum. The results showed that the four different chelating agents and organic acids had little effect on the biomass of the roots, stems, and leaves of X. sibiricum. However, they had different effects on the concentrations and accumulation of Cd and As in various organs of X. sibiricum. Compared with the those in the CK treatment, EDTA, SAP, CA, and MA significantly increased the Cd concentrations in the leaves of X. sibiricum by 44.1%, 32.4%, 41.2%, and 38.2% and the As concentrations in the roots of X. sibiricum by 89.6%, 7.4%, 94.8%, and 61.5%, respectively. The four treatments (EDTA, SAP, CA, and MA) improved the total Cd accumulation of X. sibiricum, with increasing ranges, respectively, of 70.2%, 29.4%, 28.9%, and 33.1%, and the As accumulation increased by 67.0%, 19.6%, 81.9%, and 40.8%, respectively, compared with that of the CK treatment. The four chelating agents and organic acids had different effects on the Cd and As bioconcentration factor and transfer factor of various organs of X. sibiricum. Treatments with EDTA, SAP, CA, and MA resulted in a decrease of 32.7%-38.2% in soil Cd concentrations and a decrease of 14.6%-20.5% in soil As concentrations. These four chelating agents can be used for enhancing the efficiency of extraction Cd and As heavy metals by X. sibiricum.

[Effects of Different Exogenous Plant Hormones on the Antioxidant System and Cd Absorption and Accumulation of Rice Seedlings Under Cd Stress].

In order to explore the effects of the exogenous addition of plant hormones on the antioxidant system and Cd absorption and accumulation of rice seedlings under Cd stress, the transportation and accumulation of Cd was reduced in plants to alleviate the stress of Cd on the rice. With the rice seedlings of Zhongjiazao 17 as the research object, a hydroponic experiment was carried out with three Cd concentration treatments (0, 5, and 25 µmol·L-1), and four exogenous plant hormone treatments:no plant hormones, 100 µmol·L-1 melatonin (MT), 0.2 µmol·L-1 2,4-epibrassinolide (EBL), and 0.2 µmol·L-1 jasmonic acid (JA), for a total of 12 treatments, each treatment repeated three times. The contents of Cd in the rice seedlings were analyzed, as well as the content of MDA, POD, CAT, and reduced GSH in the shoots and roots of the rice seedlings. The results indicated that under the stress of 5 µmol·L-1 and 25 µmol·L-1 Cd, the addition of MT, EBL, and JA significantly reduced the MDA content of the shoots by 11%-24%, and the roots and shoots were healthy. On the contrary, the addition of the three exogenous substances all caused an increase in the MDA content in the root system, but the effects of MT and EBL were obvious. Under the 5 µmol·L-1 Cd stress, compared with CK, the MDA contents increased by 45.5% and 20.0% respectively; under 25 µmol·L-1 Cd stress, they increased by 46.2% and 19.8%. The exogenous addition of plant hormones can significantly increase the activity of POD and CAT in the shoots and underground parts of the rice seedlings and reduce the contents of GSH and Cd. Under the 5 µmol·L-1 Cd stress, the Cd content in the shoots of rice plants decreased by 39.4%, 40.1%, and 51.6%, the roots were reduced by 38.9%, 40.2%, and 7.0%. Under the 25 µmol·L-1 Cd stress, the aboveground Cd content was reduced by 18.9%, 14.5%, and 35.6%, and the roots were reduced by 85.3%, 81.1%, and 56.5%. By exogenously adding low-concentration plant hormones MT, EBL, and JA, the stress of Cd on the rice can be alleviated, and the toxic effect of Cd on rice can be reduced.

[Effects of Exogenous Spermidine on Seed Germination and As Uptake and Accumulation of Rice Under As5+ Stress].

As pollution in farmland has a toxic effect on the growth of crops, which reduces their yield and quality. The effects of exogenous spermidine (Spd) on rice seed germination and seedling growth under As5+ stress were studied. The results showed that exogenous Spd could promote the germination of rice seeds under As5+ stress, improve the germination potential and germination rate of seeds, and promote the growth of seedling roots. The addition of Spd could increase the activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) of rice seedlings and roots under As5+ stress, and reduce the content of malondialdehyde (MDA) in rice buds and roots. When As5+ concentration was 25 µmol·L-1, adding 500 µmol·L-1 and 1000 µmol·L-1 Spd, MDA content in rice roots was decreased by 12.3% and 31.3% and CAT activity of rice shoots was increased by 105.1% and 101.4%, and CAT activity of rice roots was increased by 29.9% and 57.1%, respectively. The addition of Spd also affected the uptake and accumulation of As in rice. When the concentration of As5+ was 25 µmol·L-1, adding 500 µmol·L-1 and 1000 µmol·L-1 Spd, the concentration of As in rice shoots decreased by 69.4% and 75.1%, and As concentration in rice roots decreased by 7.6% and 24.4%, respectively. Spd could therefore effectively alleviate the toxic effect of As5+ on rice.

[Effects of Rice Straw Addition on Methanogenic Archaea and Bacteria in Two Paddy Soils].

Rice straw (RS) returning has an important effect on CH4 emission in rice paddy soil. In the present study, two paddy soil types from Jiangxi (JX) and Guangdong (GD), respectively, with different amounts of added RS were incubated through microcosmic anaerobic incubation experiments to investigate the responses of methanogenic archaea and bacteria communities after relatively long-term incubation. The different amounts of added RS affected methanogenic archaea community structures in the JX soil to some extent but did not affect the GD soil. The mcrA gene copy number increased with an increase in RS amount in both soils. Under the same amount of RS, the copy number of this gene in the JX soil was greater than that in the GD soil. In addition, significant positive correlations were shown between the RS amount and the copy number of the mcrA gene, and the response of the copy number was more sensitive to the RS amount in the JX soil. Obvious differences in methanogenic archaea community structures were shown between two soils. Methanosarcinaceae, Methanocellaceae, Methanomicrobiaceae, Methanobacteriaceae, and unknown microorganism (494 bp) were detected in the JX soil, and Methanobacteriaceae, Methanosarcinaceae, and Methanocellaceae were observed in the GD soil. The bacterial communities exhibited obvious differences between the two soil types after 180 days of incubation. The bacterial diversity in the GD soil was higher than that in the JX soil, although the amounts of dominant bacteria in the JX soil, including Bacillus, Desulfovirgula, Thermosporothrix, Acidobacteria/Gp1, Acidobacteria/Gp3, and Ktedonobacter, were higher than those of the GD soil, including Longilinea, Acidobacteria/Gp6, Bellilinea, and Thermosporothrix. RS application promoted the growth of methanogenic archaea as important substrates. Moreover, different structures of methanogens and bacteria were shown between the two soil types after relatively long-term incubation.

[Effect of Boron-antimony Interaction on the Uptake and Accumulation of Antimony and Boron by Rice Seedling].

Effect of interactions between boron (B) and antimony on the uptake and accumulation by rice (Oryza sativa L.) seedling was investigated in solution culture. The results showed that Sb(III) and Sb(V) could inhibit rice growth and Sb(III) was more toxic than Sb(V). Concentrations of B in rice roots and shoots were significantly affected by the addition of Sb(III) and Sb(V). The addition of 30 µmol x L(-1) Sb(III) could significantly decrease B of rice shoots and roots by 57.6% and 75.6%, and 30 µmol x L(-1) Sb(V) could decrease B of rice roots by 16.0%, compared with the control treatment, when the B concentration was 0.5 mg x L(-1). Equally, adding B also significantly affected the concentrations of Sb in rice roots and shoots. The addition of 2.0 mg x L(-1) B could decrease the concentrations of Sb in rice roots and shoots,by 39.1% and 9.2%, respectively, compared with 0.5 mg x L(-1) B, when the Sb(III) concentration was 10 µmol x L(-1). Adding 2.0 mg x L(-1) B could decreasd Sb concentrations in rice roots by 13.9%, compared with 0.5 mg x L(-1) B, when the Sb(V) concentration was 10 µmol x L(-1). Furthermore, adding B had significant effect on bioaccumulation factor and distribution ratio of Sb in rice roots and shoots. The results of the study demonstrated that Sb pollution in farmland could be alleviated by adding B fertilizer, thus protecting human health from Sb pollution.

Methane production and methanogenic archaeal communities in two types of paddy soil amended with different amounts of rice straw.

Soil type and returning straw to the field are the important factors that regulate CH4 formation in paddy soil, and the variations of biogeochemical parameters and methanogens communities play important roles in the formation of CH4 . In the present study, two paddy soil types [silt loam soil (JX) and silty clay loam soil (GD)] with different amounts of rice straw additions were incubated under anaerobic conditions to investigate the relationship between CH4 production, biogeochemical variations, and methanogenic archaeal communities. Straw incorporation significantly stimulated CH4 production in two soil types. CH4 production in JX soil was higher than the GD soil with equal straw addition. Significant differences between biogeochemical parameters and methanogenic archaeal communities were observed between two soil types. Straw addition increased archaeal 16S rRNA genes and mcrA genes copy numbers, especially in JX soil. Multiple regression analysis indicated that variations in H2 , sulfate, Fe (II) concentrations, archaeal 16S rRNA genes and mcrA genes copy numbers, methanogens diversity index, and the relative abundance of Methanosarcinaceae and Methanobacteriaceae together influenced CH4 production in two soil types. These results indicated that methane production was influenced by the comprehensive effects of biotic and abiotic factors in paddy soils.

Quantitative analyses of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) large-subunit genes (cbbL) in typical paddy soils.

The Calvin cycle is known to be the major pathway for CO2 fixation, but our current understanding of its occurrence and importance in paddy soils is poor. In this study, the diversity of three ribulose-1,5-bisphosphate carboxylase/oxygenase large-subunit genes (cbbLG, cbbLR, cbbM) was investigated by clone library, T-RFLP, qPCR, and enzyme assay in five paddy soils in China. The cbbLG sequences revealed a relatively low level of diversity and were mostly related to the sequences of species from Thiobacillus. In contrast, highly diverse cbbLR and cbbM sequences were dispersed on the phylogenetic trees, and most of them were distantly related to known sequences, even forming separate clusters. Abundances of three cbbL genes ranged from 10(6) to 10(9) copies g(-1) soil, and cbbLR outnumbered cbbM and cbbLG in all soil samples, indicating that cbbLR may play a more important role than other two cbbL genes. Soil properties significantly influenced cbbL diversity in five paddy soils, of which clay content, C/N ratio, CEC, pH, and SOC correlated well with variations in microbial composition and abundance. In summary, this study provided a comparison of three cbbL genes, advancing our understanding of their role in carbon sequestration and nutrient turnover in the paddy soil.

Combined effect of iron and zinc on micronutrient levels in wheat (Triticum aestivum L.).

A nutrient solution experiment was conducted to investigate the effect of Fe and Zn supply on Fe, Zn, Cu, and Mn concentrations in wheat plants. The experiment used a factorial combination of two Fe levels (0 and 5 mg l(-1)) and three Zn levels (0, 0.1 and 10 mg I(-1)). The supply of Fe (5 mg l(-1)) and Zn (0.1 mg l(-1)) increased plant dry weight and leaf chlorophyll content compared to the Fe or Zn deficient (0 mg 11) treatments. However, excess Zn supply (10 mg l(-1)) reduced plant dry weights and leaf chlorophyll content. Iron supply (5 mg l(-1)) reduced wheat Zn concentrations by 49%, Cu concentrations by 34%, and Mn by 56% respectively. Zinc supply (10 mg l(-1)) reduced wheat Fe concentrations by an average of 8%, but had no significant effect on Cu and Mn concentrations. Stepwise regression analyses indicated that Zn, Cu, and Mn concentrations were negatively correlated with root- and leaf-Fe concentrations, but positively correlated with stem-Fe concentrations. Leaf-Mn concentrations were negatively correlated with root-, stem- and leaf-Zn concentrations.