Overproduction of reactive oxygen species involved in the pathogenicity of Fusarium in potato tubers

Differences in virulence between Fusarium sulphureum and Fusarium sambucinum were compared. Changes in reactive oxygen species production and metabolism in inoculated slices of potato tubers were also compared. The result showed that Fusarium infection induced significant production of ROS, lipid peroxidation and loss of cell membrane integrity, but low activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX). Compared to F. sambucinum, F. sulphureum led larger lesion diameters on potato tubers and slices. It resulted in more superoxide anion ($O_2^{-}$) and earlier peak of hydrogen peroxide (H₂O₂), but lower activity of catalase (CAT) and APX, and accompanied with higher malondialdehyde (MDA) content and lower cell membrane integrity. These findings suggested that overproduction of ROS involved in the pathogenicity of Fusarium in potato tubers.     

巨尾桉EuGR1基因的克隆及其低温胁迫下的表达特性分析

本研究通过反转录PCR方法克隆了巨尾桉谷胱甘肽还原酶（Glutathione reductase,简称GR）基因,该基因定位于巨尾桉细胞质、长度为1485 bp,在NCBI申请基因注册（GenBank Accession Number KU904639）。构建了pET-EuGR1原核表达载体,酶活检测表明转化菌株GR活性较高。利用实时定量 PCR分析巨尾桉EuGR1的时空表达特性,结果表明：EuGR1的表达量随着巨尾桉叶片的成熟而降低,在幼叶中表达量最大,近根部的叶片表达量最低;在巨尾桉组培苗中,EuGR1在茎中表达量最大,叶中表达量较低,根中表达量最低。通过转基因抗寒巨尾桉温室苗研究EuGR1基因在低温胁迫下的表达模式,发现常温和低温胁迫下耐寒性强的株系其EuGR1的表达量较高（如P40、P41、P52）,耐寒性弱的株系其EuGR1的表达量较低（如P36、F44、F76）,说明巨尾桉EuGR1的表达量与植株的抗寒能力具有相关性。随着低温胁迫时间的延长,EuGR1的表达量在36 h后出现降低趋势,表明EuGR1在桉树耐低温胁迫的前期发挥作用较大。     

Regulation of mycorrhiza development in durum wheat by P fertilization: Effect on plant nitrogen metabolism

The aim of this work was to study the effect of arbuscular mycorrhizal fungus Glomus mosseae on growth and nitrogen (N) metabolism of durum wheat (Tritcum durum) under various P soil contents. The analyses were extended to macro and micronutrient tissue concentrations, nitrate reductase and glutamine synthetase activities, as well as protein, aminoacids, pyridine dinucleotides and adenine nucleotides. Arbuscular mycorrhiza increased wheat growth in soil in which P availability was low and nitrate was the dominant N form. The root colonization occurred at the highest level in plants grown in limiting soil P and was inversely related to soil P content. The micorrhizal wheat plants contained also the highest concentrations of macro (P, K, Ca, N) and micronutrients (Fe, Zn, Mn) as well as free amino acids, protein, NAD, NADP, AMP, ADP, ATP in roots and leaves. In particular, the micronutrient tissue concentrations (Zn, Mn) supported that mycorrhiza actively modulated their uptake limiting interferences and optimizing growth better than the plant roots, like a very efficient “rootstock”. Control plants grown at the highest soil P did not reach the same concentration as the mycorrhizal plants. Nitrate reductase activities in the roots of mycorrhizal plants were higher than in the control ones, while glutamine synthetase activities were highest in the leaves. Protein and amino acids concentrations, as well as AMP, ADP, ATP, NAD(P), and NAD(P)H were also higher than in the control. Among the free amino acids in the roots, the high levels of glutamine, asparagine, arginine, support the view that ammonium was transferred through the arbuscules to the root cells where it was re‐assimilated in the cortical cells, forming high N : C ratio‐amino acids. They were transferred to the leaves where all the other N compounds could be largely synthesized using the carbon skeletons supplied by photosynthesis.     

耕作与秸秆还田方式对稻田N_2O排放、水稻氮吸收及产量的影响

保护性耕作是改善农田土壤肥力的重要举措,然而其对作物氮吸收与产量的作用尚不明确。为此,本试验于2016—2017年稻季在湖北省武穴市花桥镇,设置常规翻耕与免耕两种耕作方式以及前茬作物秸秆全量还田与不还田两种秸秆还田方法,研究耕作与秸秆还田方式对稻田土壤N_2O排放、根系酶活性、水稻氮吸收与产量的影响。结果表明,耕作方式显著影响土壤N_2O排放,但不影响根系硝酸还原酶与谷氨酰胺合成酶活性、水稻氮吸收与产量。与翻耕处理相比,免耕处理2016年和2017年土壤N_2O排放量分别显著提高了12.5%～18.2%和21.1%～38.6%。秸秆还田显著影响土壤N_2O排放量、根系酶活性、水稻氮吸收与产量。相对于秸秆不还田处理,秸秆还田处理2016年和2017年土壤N_2O排放量分别显著提高了38.5%～45.5%和13.1%～29.5%。秸秆还田处理相对于不还田处理根系硝酸还原酶与谷氨酰胺合成酶活性分别显著增加了6.7%～45.9%和9.0%～46.7%,水稻氮吸收量提高了12.5%～26.0%,产量增加了9.4%～12.6%。本文认为,虽然秸秆还田提高了水稻氮吸收与产量,但也促进了土壤N_2O的排放,因此在评估保护性耕作稻田温室效应时应加强对温室气体(CH4和N_2O)排放和土壤碳固定影响的长期监测,以期为发展低碳稻作提供理论依据和技术支撑。     

Involvement of heme synthesis in the growth stimulation of maize seedlings by 5‐aminolevulinic acid

The growth of maize seedlings was stimulated by shoot‐applied 5‐aminolevulinic acid 2 days after treatment at 90 and 120 μmol L^?1. The effects of 5‐aminolevulinic acid on the activity of nitrate reductase (EC 1.6.6.2) and nitrite reductase (EC 1.7.7.1) and the chlorophyll, ammonium, heme and total free amino acid content were investigated by using maize seedlings to clarify the involvement of nitrogen metabolism and heme synthesis in the growth stimulation. 5‐Aminolevulinic acid increased the level of nitrate reductase activity at 90 μmol L^?1 and the ammonium and heme content at 90 and 120 μmol L^?1 2 days after treatment. The total amino acid content increased by 90 and 150 μmol L^?1 5‐aminolevulinic acid 2 and 3 days after treatment, respectively. However, no significant change was observed in the activity of nitrite reductase or the chlorophyll content after the 5‐aminolevulinic acid treatment. These results suggest that the enhancement of nitrogen metabolism by nitrate reductase activation is involved in the 5‐aminolevulinic acid‐induced stimulation of maize seedling growth. The activation of nitrate reductase might be related to an increase in the heme content following the 5‐aminolevulinic acid treatment.     

Identification of a 4-Deoxy-l-erythro-5-hexoseulose Uronic Acid Reductase,FlRed, in an Alginolytic Bacterium Flavobacterium sp. Strain UMI-01

In alginate-assimilating bacteria, alginate is depolymerized to unsaturated monosaccharide by the actions of endolytic and exolytic alginate lyases (EC 4.2.2.3 and EC 4.2.2.11). The monosaccharide is non-enzymatically converted to 4-deoxy-l-erythro-5-hexoseulose uronic acid (DEH), then reduced to 2-keto-3-deoxy-d-gluconate (KDG) by a specific reductase, and metabolized through the Entner–Doudoroff pathway. Recently, the NADPH-dependent reductase A1-R that belongs to short-chain dehydrogenases/reductases (SDR) superfamily was identified as the DEH-reductase in Sphingomonas sp. A1. We have subsequently noticed that an SDR-like enzyme gene, flred, occurred in the genome of an alginolytic bacterium Flavobacterium sp. strain UMI-01. In the present study, we report on the deduced amino-acid sequence of flred and DEH-reducing activity of recombinant FlRed. The deduced amino-acid sequence of flred comprised 254 residues and showed 34% amino-acid identities to that of A1-R from Sphingomonas sp. A1 and 80%–88% to those of SDR-like enzymes from several alginolytic bacteria. Common sequence motifs of SDR-superfamily enzymes, e.g., the catalytic tetrad Asn-Lys-Tyr-Ser and the cofactor-binding sequence Thr-Gly-x-x-x-Gly-x-Gly in Rossmann fold, were completely conserved in FlRed. On the other hand, an Arg residue that determined the NADPH-specificity of Sphingomonas A1-R was replaced by Glu in FlRed. Thus, we investigated cofactor-preference of FlRed using a recombinant enzyme. As a result, the recombinant FlRed (recFlRed) was found to show high specificity to NADH. recFlRed exhibited practically no activity toward variety of aldehyde, ketone, keto ester, keto acid and aldose substrates except for DEH. On the basis of these results, we conclude that FlRed is the NADH-dependent DEH-specific SDR of Flavobacterium sp. strain UMI-01.     

维生素A调节动物一氧化氮的生成及其相关机制

动物机体由于旺盛的新陈代谢或在受到外界有害因素刺激的情况下会产生大量一氧化氮(NO),进而损伤细胞中的蛋白质、类脂膜和DNA,引发细胞炎症并阻断细胞信号通路,使机体产生氧化应激。维生素A可以有效地调控NO的生成,提高机体抗氧化水平并清除自由基,预防细胞炎症及氧化应激的发生。本文主要综述了维生素A对动物NO生成的调节作用及其相关机理的研究进展,对今后深入研究其调节机理、科学补充维生素A及提高机体的抗氧化功能具有一定参考价值。