低浓度Na2CO3胁迫下星星草幼苗保护酶活性与活性氧之间的关系

对低浓度(0.2%)Na2CO3胁迫和无胁迫正常生长的星星草幼苗的相对电导率、可溶性蛋白质含量、SOD活性、POD活性、CAT活性、MDA含量、H2O2含量和产生O2-·速率的研究结果表明,星星草幼苗各保护酶、活性氧及相对电导率之间存在一定的变化关系,这种变化关系在0.2% Na2CO3胁迫和无胁迫正常生长的星星草幼苗间存在差异.在一定程度上揭示了抗盐碱植物在正常生长情况下与碱胁迫下的活性氧(H2O2和O2-·)代谢可能存在不同的调节机制.     

Nitrogen metabolism in flag leaf and grain of wheat in response to irrigation regimes

Although scarcity of irrigation water is one of the key limiting factors for wheat production in many regions of the world, by using partial irrigation at strategic times during the growing season, it might be possible to enhance productivity. We measured the changes in various parameters related to nitrogen (N) metabolism in flag leaf and grain of wheat (Triticum aestivum L.) plants (cv. Jinan 17 and Lumai 21), which were subjected to five irrigation regimes until physiological maturity. Severely deficient or excessive irrigation during grain filling decreased the photosynthetic rate (A), the concentrations of N, free amino acid, and soluble protein, as well as the activities of nitrate reductase (NR) and glutamine synthetase (GS) and increased malondialdehyde (MDA) accumulation and endopeptidase (EP) activity, though grain protein concentration might mainly depend on genotype. The activities of NR and GS were significantly positively correlated with A, but those of EP were significantly negatively correlated with A. The results indicate that while severe water stress aggravates the adverse effect on nitrogen metabolism, excessive soil moisture is also not useful during the grain‐filling stage, resulting in lower grain yield and quality. Our results suggest that applying an optimal irrigation regime in wheat fields still plays an important role in the improvement of grain yield and quality.     

Application of para-nitrophenol (pNP) enzyme assays in degraded tropical soils

Enzyme activities have been used as indicators of soil quality and changes in biogeochemical function due to management or perturbations. The objective of this study was to answer a number of methodological questions regarding sampling schemes, sample handling recommendations, and assay procedures to facilitate the use of enzyme assays in the tropical highlands of East Africa. We used para-nitrophenol (pNP) based substrates for five enzymes: β-glucosidase, cellobiohydrolase, chitinase, acid phosphatase, and alkaline phosphatase. In the first experiment, we examined sampling procedures and compared the results of determining enzyme activities on a plot using composite or discrete samples. Composite samples usually had higher activities than the means of individual cores (P<0.05), but relative ranking of sites was the same if analyses were based on composite or discrete samples. In the second experiment, we examined the effects of storage time and conditions on enzyme activity. Enzyme activity degraded rapidly in frozen samples, but was better maintained in samples stored at 4 °C. Phosphatase and cellobiohydrolase activity declined after 14 days of storage, while the activity of the other enzymes remained close to the values of fresh samples for 28 or more days. In the third experiment, we examined the effect of the addition of an antiseptic, toluene, to prevent bacterial growth during the assay. We found no consistent toluene effect (P>0.4), probably because the assays were of short duration and microbial growth was minimized. Finally, we looked at the incubation time necessary to produce reliable results. Phosphatases, with relatively high activities could reliably be determined in 2 h incubations, but the other enzymes had much lower activities and required longer incubation times for reliable determination. For the enzymes we looked at, 4 h was a good standard time for determining the activity of even the lowest activity enzymes. The results of this study provide practical guidelines for applying these enzyme assays in the degraded tropical soils.     

Bovine serum albumin and Triton X-100 greatly increase phosphomonoesterases and arylsulphatase extraction yield from soil

Extraction of arylsulphatase (aryS), acid (acP) and alkaline phosphomonoesterase (alkP) from six different soils using sodium pyrophosphate (0.14 M, pH 7.1) yielded brown extracts displaying enzymatic activity mostly below detection limit. Tris-HCl (50 mM, pH 7.5) gave an extraction yield, on average, lower than 0.5%, but addition of Triton X-100 or bovine serum albumine (BSA) to Tris buffer increased the extraction yield 2-8 times. When both Triton X-100 and BSA were added to the buffer, the extraction yield was more than additive and reached 2-13% for acP, 2-5% for alkP and 3-6% for aryS, depending on the soil. In addition, these extracts were colourless or at most light yellow, showing that besides the high yield enzymes were extracted along with negligible amounts of humic substances.     

Effect of differently post-treated dewatered sewage sludge on β-glucosidase activity,microbial biomass carbon,basal respiration and carbohydrates contents of soils from limestone quarries

This work has evaluated the effects of thermally dried (TDS) or composted (CDS) dewatered sewage sludge on β-glucosidase activity, total (TCH) and extractable (ECH) carbohydrate content, microbial biomass carbon and basal respiration of soils from limestone quarries under laboratory conditions. Two doses (low and high) of the dewatered sludge (DS) or of the respective TDS or CDS were applied to a clayey and a sandy soil, both coming from working quarries. The soil mixtures and the controls (soils with no added sludge) were incubated for 9 months at 25°C and 30% of field capacity. The addition of sludge increased all the studied soil parameters, and the increase depended on the amount of sludge. Except in the case of TCH and ECH, the enhancing effect decreased with time, but at the end of incubation, parameters of the treated soils were higher than those of the control. The rank order of the initial stimulating effect was soil–TDS ≥ soil–DS ≥ soil–CDS, and probably, this order depended on the proportion of stable organic matter, which was the lowest in the TDS. Values of metabolic quotient (qCO₂) were higher at the lower dose, and they did not change during incubation in the CDS-treated soils. Both TCH and ECH were the parameters with the greatest significant sludge and dose effects. Basal respiration, microbial biomass carbon and β-glucosidase activity were the best measured parameters in distinguishing the long-term effects of the three sludge types over the soils.     

l-Asparaginase activity of soils

Summary A simple, precise, and sensitive method to assay l-asparaginase (l-asparagine amidohydrolase, EC 3.5.1.1) activity in soils is described. This method use steam distillation to determine the NH _inf4 ^sup+ produced by l-asparaginase activity when soil is incubated with buffered (0.1 M THAM, pH 10) l-asparagine solution and toluene at 30°C for 2 h. The procedure developed gives quantitative recovery of NH _inf4 ^sup+ -N added to soils and does not cause chemical hydrolysis of l-asparagine. The optimum buffer pH for NH _inf4 ^sup+ -N released by l-asparaginase activity in soils was 10. This enzyme was saturated with 50 mM l-asparagine, and the reaction rate essentially followed zero-order kinetics. The d-isomer of asparagine was also hydrolyzed in soils, but at only 16% of the activity of the l-isomer at a saturating concentration of the substrate. The optimal temperature for the soil l-asparaginase reaction occurred at 60°C and denaturation began at 65°C. The Arrhenius equation plot for l-asparaginase activity in three selected soils was linear between 10 and 50°C. The activation energy values of this enzyme ranged from 20.2 to 34.1 (average 26.6) kJ mol^-1. Application of three linear transformations of the Michaelis-Menten equation showed that the K _m values of l-asparaginase in nine soils ranged from 2.6 to 10.0 (average 6.1) mM and the V _max values ranged from 9 to 131 g NH _inf4 ^sup+ -N released g^-1 soil 2 h^-1. The temperature coefficients (Q ₁₀) for soil l-asparaginase activity ranged from 1.12 to 1.70 (average 1.39). Steam sterilization (121°C for 1 h), formaldehyde, and NaF decreased the activity but the presence of toluene increased the amount of NH _inf4 ^sup+ released. Treatment of soils with dimethylsulfoxide completely destroyed l-asparaginase activity. The use of sulfhydryl reagents indicated that a free sulfhydryl moiety was required to maintain the active enzyme. l-Asparaginase activity in soils was increased by 13 to 18% in the presence of THAM buffer prepared to contain 5 mM Ca²⁺ and Mg²⁺, respectively.     

Influence of smoke exposure on soil enzyme activities and nitrification

Summary Soil was exposed to red phosphorous/butyl rubber (RP/BR) aerosols at various relative humidities in a recirculating environmental wind tunnel. Soil microbial and enzymatic activities were measured immediately after exposure and periodically thereafter for 56 days. The nitrification potential was significantly reduced in soil amended with ammonium sulfate and exposed to RP/BR smoke, and could be related to a decline in soil pH. The rate of nitrate formation in unamended soil with time was also reduced, but by 57 days postexposure, concentrations were similat to those of unexposed controls in all but the thinnest soil lense. Soil dehydrogenase and phosphatase enzyme activities were sensitive to RP/BR smoke and in some treatments no activity was detected. The measured activities did not recover within the 56-day postexposure period and in some cases declined. Soil lense thickness was the greatest factor controlling the degree of RP/BR effects, indicating that injury to soil microbial and enzymatic activities may be surficial. Deposition of smoke particles increased with increasing relative humidity, which had a significant impact on the activities measured.     

Physiological,Biochemical, and Molecular Effects of In Vitro Induced Iron Deficiency in Peach Rootstock Mr.S 2/5

Abstract

On calcareous soils, carbonate induced iron deficiency can have heavy effects on growth and development of several fruit crops. Leaf chlorosis, biochemical, and ultrastructural alterations are the first symptoms causing severe damages to yield and productivity. In this work, some physiological, biochemical, and molecular aspects of iron deficiency stress induced on the peach rootstock Mr.S 2/5 in vitro were studied. The aim was to demonstrate if in vitro culture can be used as a valid and fast method to evoke iron deficiency symptoms and to study plant responses to this kind of abiotic stress. Two different treatments were carried out and compared to a control (MS medium): plantlets grown on MS medium completely free of iron and on MS medium containing 1 mM potassium bicarbonate. After 10 and 20 days from the beginning of the treatments fresh and dry weight, chlorophyll, and carotenoids content were measured. Superoxide dismutase and catalase total activity was measured, and gene expression was analyzed by using etherologous probes (Sod1, Sod3, Sod4, and Cat1) obtained from maize. In the absence of iron or in the presence of bicarbonate Mr.S 2/5 plantlets showed a significant decrease in growth, as quantified by fresh and dry weight. The plantlets showed a severe chlorosis due to a reduction in chlorophyll and carotenoids concentration. Iron deficiency stress caused a reduction of the activity of catalase and superoxide dismutase, while inducing an increase in gene expression.     

Boron Induced Oxidative Stress,Antioxidant Defence Response and Changes in Artemisinin Content in Artemisia annua L.

Boron is an essential plant micronutrient and the range between deficient and toxic levels of boron is narrow for most of the plants. Like other elements, boron becomes toxic to growth at high concentrations. High boron concentrations in soil reduce crop productivity in many areas of the world. The effect of increasing levels of boron (0, 0.50, 1.00, 1.50, 2.00 mm ) on oxidative stress, antioxidant defence response and changes in artemisinin content in Artemisia annua were investigated in the present study. Boron toxicity reduced the growth parameters viz. stem height, fresh weight and dry weight. Treatments induced oxidative stress resulting in lower net photosynthetic rate, stomatal conductance, internal CO₂ and total chlorophyll content. The increased activities of antioxidant enzymes like CAT, POX and SOD were also noted in response to increasing levels of boron stress. However, H₂O₂ and artemisinin content were found to be high up to 1.00 mm concentration of boron compared to control, and on applying higher doses, further reduced contents were obtained. Thus, the results suggest that a mild stress of boron can be utilized for enhanced artemisinin production.     

亚硝酸盐对红螯光壳螯虾不同组织免疫相关酶活性及超微结构的影响

应用透射电镜技术,结合生物酶测定,研究了水体中不同浓度亚硝酸盐胁迫下红螯光壳螯虾肝胰腺、鳃和肌肉组织中免疫相关酶的活性变化,以及对肝胰腺和鳃的形态学影响。结果显示,与对照组相比,亚硝酸盐胁迫下,3种组织的ACP、AKP、SOD以及GSH-PX的活性都显著降低(P<0.05);随着亚硝酸盐浓度增加,酶活力呈现降低的趋势;鳃组织Na+,K+-ATPase和Ca2+,Mg2+-ATPase的活性也显示出随亚硝酸盐浓度升高而降低的趋势。超微结构显示,随着亚硝酸盐浓度增加,鳃角质层受损、断裂;上皮细胞排列疏松、空泡化;细胞器变形;鳃腔内也出现空泡化现象,血细胞变形。肝胰腺上皮细胞排列杂乱无章,细胞裂解,空泡化;微绒毛受损、断裂,肝小管间距扩大、结缔组织变得稀薄,血细胞变形;高浓度组R细胞的脂滴减少,核膜解体,细胞膜破裂,空泡化加剧;F细胞的核糖体减少,空泡化加剧,内质网水肿。研究说明亚硝酸盐对红螯光壳螯虾3种组织的免疫相关酶活产生影响,并损伤肝胰腺和鳃的形态学结构,影响其生物学功能。