Modification of chromium (VI) phytotoxicity by exogenous gibberellic acid application in <Emphasis Type="Italic">Pisum sativum</Emphasis> (L.) seedlings

Effects of exogenous gibberellic acid (GA; 10 and 100 μM) application on growth, protein and nitrogen contents, ammonium (NH₄ ⁺) content, enzymes of nitrogen assimilation and antioxidant system in pea seedlings were investigated under chromium (VI) phytotoxicity (Cr VI; 50, 100 and 250 μM). Exposure of pea seedlings to Cr and 100 μM GA resulted in decreased seed germination, fresh and dry weight and length of root and shoot, and protein and nitrogen contents compared to control. Compared to control, Cr and 100 μM GA led to the significant alteration in nitrogen assimilation in pea. These treatments decreased root and shoot nitrate reductase (NR), glutamine synthetase (GS) and glutamine 2-oxoglutarate aminotransferase (GOGAT) activities (except 50 μM Cr alone for GOGAT) while glutamate dehydrogenase (GDH) activity and NH₄ ⁺ content increased. Compared to control, the root and shoot activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased (except APX activity at 250 μM Cr + 100 μM GA) while catalase (CAT), glutathione reductase (GR) and dehydroascorbate reductase (DHAR) activities were decreased (except GR at 100 μM GA alone) following exposure of Cr and 100 μM GA. Total ascorbate and total glutathione in root and shoot decreased by the treatments of Cr and 100 μM GA while their levels were increased by the application of 10 μM GA compared to Cr treatments alone. It has been reported that application of 10 μM GA together with Cr alleviated inhibited levels of growth, nitrogen assimilation and antioxidant system compared to Cr treatments alone. This study showed that application of 10 μM GA counteracts some of the adverse effects of Cr phytotoxicity with the increased levels of antioxidants and sustained activities of enzymes of nitrogen assimilation; however, 100 μM GA showed apparently reverse effect under Cr phytotoxicity.     

Selenium protects sorghum leaves from oxidative damage under high temperature stress by enhancing antioxidant defense system

Oxidative stress is commonly induced when plants are grown under high temperature (HT) stress conditions. Selenium often acts as an antioxidant in plants; however, its role under HT-induced oxidative stress is not definite. We hypothesize that selenium application can partly alleviate HT-induced oxidative stress and negative impacts of HT on physiology, growth and yield of grain sorghum [Sorghum bicolor (L.) Moench]. Objectives of this study were to investigate the effects of selenium on (a) leaf photosynthesis, membrane stability and antioxidant enzymes activity and (b) grain yield and yield components of grain sorghum plants grown under HT stress in controlled environments. Plants were grown under optimal temperature (OT; 32/22 °C daytime maximum/nighttime minimum) from sowing to 63 days after sowing (DAS). All plants were foliar sprayed with sodium selenate (75 mg L^?1) at 63 DAS, and HT stress (40/30 °C) was imposed from 65 DAS through maturity. Data on physiological, biochemical and yield traits were measured. High temperature stress decreased chlorophyll content, chlorophyll a fluorescence, photosynthetic rate and antioxidant enzyme activities and increased oxidant production and membrane damage. Decreased antioxidant defense under HT stress resulted in lower grain yield compared with OT. Application of selenium decreased membrane damage by enhancing antioxidant defense resulting in higher grain yield. The increase in antioxidant enzyme activities and decrease in reactive oxygen species (ROS) content by selenium was greater in HT than in OT. The present study suggests that selenium can play a protective role during HT stress by enhancing the antioxidant defense system.     

Nitrogen assimilation in opaque and normal sorghum during grain development

Activity of key nitrogen assimilating enzymes was studied in developing grains of high-lysine opaque sorghum P-721 and normal sorghum CSV-5. The higher percentage of protein in opaque sorghum was mainly due to lower starch content since protein per grain was less than in CSV-5. During grain development, albufn and globulin decreased while prolafne and glutelin increased. Prolafne content in CSV-5 was higher than in opaque sorghum. Average nitrate reductase activity in flag and long leaf were similar in both the varieties. The nitrate reductase activity decreased during grain development. Glutamate dehydrogenase activity was higher during early development and lower at later stages in opaque sorghum than in CSV-5. Glutamate oxaloacetate transaminase activity was higher and glutamine synthetase lower in opaque sorghum than in CSV-5 grains during development. Glutamate synthase activity was higher in opaque sorghum up to day 20 and lower thereafter than in CSV-5. It is suggested that reduced activities of glutamine synthetase as well as glutamate synthase in opaque sorghum as compared to CSV-5 during later stages of development may restrict protein accumulation in the former.     

施氮时期对高产夏玉米氮代谢关键酶活性及抗氧化特性的影响

选用玉米品种登海661和郑单958为材料,研究了高产条件下施氮时期对夏玉米产量、氮素利用率、氮代谢相关酶及抗氧化酶活性的影响.结果表明:拔节期一次性施氮不利于夏玉米产量提高和氮素积累,分次施氮且增施花粒肥显著提高了植株和籽粒的吸氮量,并提高了籽粒产量.拔节期、10叶期、花后10d按2∶4∶4施氮,登海661产量最高可达14123.0kg· hm-2;基肥、拔节期、10叶期、花后10 d按1∶2∶5∶2施氮,郑单958产量最高可达14517.1 kg· hm-2,这2种施氮方式较拔节期一次性施氮分别增产14.5％和17.5％.花前分次施氮可以显著提高开花期硝酸还原酶活性;登海661和郑单958在花后0～42 d中,施氮处理的谷氨酰胺合成酶、谷氨酸合成酶、谷氨酸脱氢酶活性分别平均提高了32.6％、47.1％、50.4％和14.5％、61.8％、25.6％,减缓了其下降趋势;超氧化物歧化酶、过氧化氢酶活性提高了22.0％、36.6％和13.4％、62.0％,丙二醛含量显著降低.在高产条件下,分次施氮且适当增加花粒肥施入比例可以提高氮代谢相关酶活性,延缓植株衰老,促进氮素吸收利用,进而提高籽粒产量.     

植物氮代谢及其环境调节研究进展

氮代谢是植物的基本生理过程之一,也是参与地球化学循环的重要组成部分,植物氮素同化的主要途径是经过硝酸盐还原为铵后直接参与氨基酸的合成与转化,期间硝酸还原酶(NR)、谷氨酰胺合成酶(GS)、谷氨酰胺合酶(GOGAT)、天冬酰胺转氨酶(AspAT)等关键酶参与了催化和调节,以氨基酸为主要底物在细胞中合成蛋白质,再经过对蛋白质的修饰、分类、转运及储存等,成为植物有机体的组成部分,同时与植物的碳代谢等协调统一,共同成为植物生命活动的基本过程,文中概述了植物氮素同化的途径、几种关键酶的特性和调控机制,简述了氮素代谢的信号传导、植物细胞蛋白质的形成、转运、储存和降解过程,基于水分胁迫等关键生态因子对氮代谢的影响及其调节机制的评述,强调了未来需加强研究的7个方面。     

Stress studies in lentil (Lens esculenta Moench)

The response of soil exchangeable sodium percentage levels to nitrate reductase activity, nitrite reductase activity, free proline, DNA, RNA, chlorophyll a and b contents and yield components in lentil (Lens esculenta Moench)cv. PL 406 was studied in a replicated pot experiment. All the biochemical observations were recorded at four growth stages i.e. 30, 60, 90 and 120 days after sowing (DAS). Germination occurred up to exhangeable sodium percentage of 30, but plants survived only up to 25. With increasing exchangeable sodium percentage, there was a continuous decrease in chlorophyll a and b content, nitrate and nitrite reductase enzyme activities and DNA and RNA content. Increasing level of sodicity enhanced the free proline content up to 60 DAS, after which values fell.Number of pods per plant, 1000 grain weight and grain yield were significantly reduced with increasing level of sodicity, but the number of grains per pod was not affected.     

多效唑对不同品质类型花生产量、品质及相关酶活性的影响

选用高蛋白品种KB008（KB008）、高脂肪品种花17(H17)和高油酸/亚油酸（O/L）品种农大818（818）,在大田栽培条件下,研究了盛花后期叶面喷施多效唑(PBZ)对不同品质类型花生产量、品质及相关碳、氮代谢酶活性的影响.结果表明：喷施PBZ显著增加了3种品质类型花生荚果产量,原因是增加了单株结果数,降低了千克果数而提高了双仁果率.喷施PBZ不同程度地提高了3种类型花生籽仁脂肪和可溶性糖含量,降低了蛋白质含量,显著增加了高脂肪品种H17的O/L值.PBZ使高O/L值品种818的脂肪含量增加显著,同时其蛋白质含量显著降低,而对其他两品种的蛋白质和脂肪含量影响较小.喷施PBZ均降低了3种类型花生结荚期叶片硝酸还原酶（NR）活性及结荚期和饱果期叶片谷氨酰胺合成酶和谷氨酸脱氢酶活性,818的3种酶活性降低幅度最大,KB008和H17的酶活性降幅较小;喷施PBZ均降低了3种类型花生结荚期和饱果期叶片谷草转氨酶和谷丙转氨酶活性.说明氮代谢酶活性的降低是喷施PBZ降低3种类型花生籽仁蛋白质含量的主要原因.喷施PBZ均提高了3品种结荚期和饱果期叶片蔗糖合成酶和磷酸蔗糖合成酶活性,其中显著提高了818的2种酶活性,而对KB008和H17的活性提高不显著;喷施PBZ提高了3品种结荚期和饱果期的磷酸烯醇式丙酮酸羧化酶和1,5-二磷酸核酮糖羧化酶活性,其中对818在结荚期的活性提高最显著,对H17活性提高较小.碳代谢酶活性的增强是喷施PBZ提高花生籽仁脂肪含量的生理基础.     

氮素水平对冬小麦籽粒灌浆过程中淀粉合成关键酶活性的影响

小麦籽粒灌浆过程中,淀粉合成关键酶腺苷二磷酸葡萄糖焦磷酸化酶(ADPG-PPase)、可溶性淀粉合成酶(SSS)、淀粉分支酶(SBE)和束缚态淀粉合成酶(GBSS)均随着灌浆进程呈单峰曲线变化,峰值出现在花后25d;不同氮肥施用量对灌浆前期酶活性的影响较小,而在花后20d之后影响较大;随着氮肥施用量的增加,4种酶活性均呈增加趋势,但氮肥过量时酶活性下降,表明适当增加施氮量有利于淀粉合成关键酶活性的提高。     

不同酸度酸雨对小麦花后氮硫代谢和籽粒蛋白组分的影响

酸雨是中国重要的环境问题,为研究酸雨对小麦籽粒品质的可能影响,以小麦品种扬麦15和汶农17为材料开展盆栽试验,研究了不同酸度(pH2.5、p H4.0和p H5.6)酸雨对小麦花后氮硫代谢关键酶活性和籽粒蛋白质含量及组分的影响。结果显示:酸雨处理抑制叶片硝酸还原酶(NR)活性,提高了扬麦15整个灌浆期及汶农17灌浆中后期叶片谷氨酰胺合成酶(GS)活性,促进了叶片蛋白的降解,降低了叶片可溶性蛋白含量。不同酸度酸雨提高了成熟期籽粒中蛋白质含量,酸度越强,增加幅度越大,籽粒中各蛋白组分含量和大部分氨基酸含量也有明显提高。酸雨提高了扬麦15叶片丝氨酸乙酰转移酶(SAT)和O-乙酰丝氨酸硫裂解酶(OAS-TL)活性,但对汶农17硫代谢关键酶活性影响较小,酸雨处理还提高了籽粒中二硫键和含硫氨基酸含量。可见酸雨对小麦氮硫代谢有不同程度影响,进而影响了小麦籽粒蛋白质含量和组成,酸度越强影响越大,但不同品种对酸雨响应有一定差异。     

不同环境条件下小麦氮代谢关键酶活性及籽粒品质

研究了两种环境条件下3个不同蛋白含量小麦品种的氮代谢关键酶活性及籽粒品质的差异.结果表明,龙口试验点的小麦旗叶硝酸还原酶(NR)、谷胺酰氨合成酶(GS)和籽粒谷胺酰氨合成酶活性均显著高于泰安试验点,3个品种间的酶活性顺序均为：济麦20＞优麦3号＞PH971942.优质强筋小麦品种的籽粒综合品质性状在龙口试验点的表现优于泰安试验点. 灌浆期环境因素与小麦籽粒品质和酶活性存在显著的相关性,灌浆期间的较高气温、适当干旱和寡照环境有利于提高小麦籽粒品质.龙口试验点的中、强筋小麦品种和泰安试验点的中筋小麦品种蛋白质含量与旗叶NR和GS活性均达显著正相关.小麦品种用途不同,对环境条件的要求不同,适宜的环境条件提高了氮代谢关键酶的活性,利于改善小麦品质.     

Hexavalent Chromium Reduction from Pollutant Samples by <Emphasis Type="Italic">Achromobacter xylosoxidans</Emphasis> SHB 204 and its Kinetics Study

Cr(VI) is most toxic heavy metal and second most widespread hazardous metal compound worldwide. Present work focused on Cr(VI) reduction from synthetic solutions and polluted samples by Achromobacter xylosoxidans SHB 204. It could tolerate Cr(VI) up to 1600 ppm and reduce 500 ppm with 4.5 chromium reductase enzyme units (U) having protein size 30 kDa. Changes in morphology of cells on interaction with Cr(VI) metal ion was also studied using SEM–EDX and FTIR. Microcosm studies in pollutant samples for Cr(VI) reduction and adsorption isotherm with biomass of bacterium was best fitted with Langmuir model along with kinetic studies. This study focuses on significance of Cr reduction from synthetic solutions and polluted samples by A. xylosoxidans SHB 204 and its potential for bioremediation.     

Changes in C–N metabolism under elevated CO2 and temperature in Indian mustard (Brassica juncea L.): an adaptation strategy under climate change scenario

The present study was performed to investigate the possible role of carbon (C) and nitrogen (N) metabolism in adaptation of Indian mustard (Brassica juncea L.) growing under ambient (370 ± 15 ppm) and elevated CO₂ (700 ± 15 ppm), and jointly in elevated CO₂ and temperature (30/22 °C for day/night). The key enzymes responsible for C–N metabolism were studied in different samples of Brassica juncea L. collected from ambient (AMB), elevated (ELE) and ELExT growth conditions. Total percent amount of C and N in leaves were particularly estimated to establish a clear understanding of aforesaid metabolism in plant adaptation. Furthermore, key morphological and physiological parameters such as plant height, leaf area index, dry biomass, net photosynthetic rate, stomatal conductance, transpiration, total protein and chlorophyll contents were also studied in relation to C/N metabolism. The results indicated that the C-metabolizing enzymes, such as (ribulose-1,5-bisphosphate carboxylase/oxygenase, phosphoenolpyruvate carboxylase, malate dehydrogenase, NAD-malic enzyme, NADP-malic enzyme and citrate synthase) and the N-metabolizing enzymes, such as (aspartate amino transferase, glutamine synthetase, nitrate reductase and nitrite reductase) showed significantly (P < 0.05) higher activities along with the aforesaid physiological and biochemical parameters in order of ELE > ELExT > AMB growth conditions. This is also evident by significant (P < 0.05) increase in percent contents of C and N in leaves as per said order. These findings suggested that improved performance of C–N metabolism could be a possible approach for CO₂ assimilation and adaptation in Brassica juncea L. against elevated CO₂ and temperature prevailing in climate change scenarios.     

Can genetic manipulation of plant nitrogen assimilation enzymes result in increased crop yield and greater N-use efficiency? An assessment

The literature on the relations between plant nitrogen (N) assimilation enzymes and plant/crop N assimilation, growth and yield is reviewed to assess if genetic manipulation of the activities of N assimilation enzymes can result in increased yield and/or increased N use efficiency. The available data indicate that (I) levels of N assimilation enzymes do not limit primary N assimilation and hence yield; (II) root or shoot nitrate assimilation can have advantages under specific environmental conditions; (III) for cereals, cytosolic glutamine synthetase (GS1) is a key enzyme in the mobilisation of N from senescing leaves and its activity in senescing leaves is positively related to yield; and (TV) for rice (Oryza sativd), NADH-glutamate synthase (NADH-GOGAT) is important in the utilisation of N in grain filling and its activity in developing grains is positively related to yield. In our opinion, selection of plants, from either a genetically manipulated population or genetic resources, with expression of nitrate reductase/nitrite reductase primarily in the root or shoot should increase plant/crop growth and hence yield under specific environmental conditions. In addition for cereals the selection of plants with high GS1 in senescing leaves and in some cases high NADH-GOGAT in developing grains could help maximise the retrieval of plant N in seeds.     

Chromate/nitrite interactions in Shewanella oneidensis MR-1: evidence for multiple hexavalent chromium [Cr(VI)] reduction mechanisms dependent on physiological growth conditions

Inhibition of hexavalent chromium [Cr(VI)] reduction due to nitrate and nitrite was observed during tests with Shewanella oneidensis MR-1 (previously named Shewanella putrefaciens MR-1 and henceforth referred to as MR-1). Initial Cr(VI) reduction rates were measured at various nitrite concentrations, and a mixed inhibition kinetic model was used to determine the kinetic parameters-maximum Cr(VI) reduction rate and inhibition constant [V(max,Cr(VI)) and K(i,Cr(VI))]. Values of V(max,Cr(VI)) and K(i,Cr(VI)) obtained with MR-1 cultures grown under denitrifying conditions were observed to be significantly different from the values obtained when the cultures were grown with fumarate as the terminal electron acceptor. It was also observed that a single V(max,Cr(VI)) and K(i,Cr(VI)) did not adequately describe the inhibition kinetics of either nitrate-grown or fumarate-grown cultures. The inhibition patterns indicate that Cr(VI) reduction in MR-1 is likely not limited to a single pathway, but occurs via different mechanisms some of which are dependent on growth conditions. Inhibition of nitrite reduction due to the presence of Cr(VI) was also studied, and the kinetic parameters V(max,NO2) and K(i,NO2) were determined. It was observed that these coefficients also differed significantly between MR-1 grown under denitrifying conditions and fumarate reducing conditions. The inhibition studies suggest the involvement of nitrite reductase in Cr(VI) reduction. Because nitrite reduction is part of the anaerobic respiration process, inhibition due to Cr(VI) might be a result of interaction with the components of the anaerobic respiration pathway such as nitrite reductase. Also, differences in the degree of inhibition of nitrite reduction activity by chromate at different growth conditions suggest that the toxicity mechanism of Cr(VI) might also be dependent on the conditions of growth. Cr(VI) reduction has been shown to occur via different pathways, but to our knowledge, multiple pathways within a single organism leading to Cr(VI) reduction has not been reported previously.     

Speciation dependant antioxidative response in roots and leaves of sorghum (Sorghum bicolor (L.) Moench cv CO 27) under Cr(III) and Cr(VI) stress

Growth, lipid peroxidation, H₂O₂ produciton and the response of the antioxidant enzymes and metabolites of the ascorbate glutathione pathway to oxidative stress caused by two concentrations (50 and 100 µM) of Cr(III) and Cr(VI) was studied in 15 day old seedlings of sorghum (Sorghum bicolor (L.) Moench cv CO 27) after 10 days of treatment. Cr accumulation in sorghum plants was concentration and organ dependant. There was no significant growth retardation of plants under 50 µM Cr(III) stress. 100 µM Cr(VI) was most toxic of all the treatments in terms of root and leaf growth and oxidative stress. 50 µM Cr(VI) treated roots exhibited high significant increase in superoxide dismutase (SOD), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) (p < 0.01) and significant increases in catalse (CAT), ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) (p < 0.05). A high increase in ascorbic acid (AA) level was seen in roots of 50 µM Cr(VI) treated plants in comparison with control. Levels of reduced glutathione (GSH) showed a varied and complex response in all the treatments in both plant parts. GSH/GSSG ratio was not affected by Cr(III) treatment in leaves, in contrast, roots exhibited significant reduction in the ratio. Results indicate that GSH depletion increased sensitivity to oxidative stress (Cr(VI) roots and leaves and Cr(III) 100 µM roots) and AA in tandem with APX compensated for GSH depletion by acting directly on H₂O₂ and the mechanism of defensive response in roots as well as leaves varied in its degree and effectiveness due to the concentration dependant differences observed in translocation of the element itself, reactive oxygen species (ROS) generation and enzyme inhibition based on the oxidation state supplied to the plants.     

Evidence for a role of calcium in nitrate assimilation in wheat seedlings

Severely Ca-deficient Triticum aestivum L. seedlings accumulated high levels of nitrite and moderate levels of nitrate and organic nitrogen, but contained unaltered levels of hydroxylamine. Nitrite accumulation was not related to molybdenum deficiency, or altered cellular pH. Nitrate reductase was decreased by Ca deficiency, apparently by repression of enzyme synthesis from accumulated nitrite and not by inhibition of enzyme activity. Nitrite reductase and NADP diaphorase activities were not affected by Ca deficiency, and Ca did not restore activity to nitrite reductase inactivated by cyanide. The results indicated that the role of Ca is in intracellular transport of nitrite and not in induction or activity of enzymes.     

Nitrogen Metabolism and Photosynthesis in Leymus chinensis in Response to Long-term Soil Drought

Key enzyme activities related to nitrogen metabolism, gas-exchange, chlorophyll fluorescence, and lipid peroxidation were determined in Leymus chinensis (Trin.) Tzvel. plants under four soil moisture regimes (control: 75%–80% of field moisture capacity, mild drought: 60%–65%, and moderate drought: 50%–55% as well as severe drought: 35%–40%). Severe drought significantly decreased the key enzyme activities of nitrogen anabolism such as nitrate reductase (NR, EC 1.6.6.1), glutamine synthetase (GS, EC 6.3.1.2), and glutamate dehydrogenase (GDH, EC 1.4.1.2) but increased the key enzyme activities of nitrogen catabolism such as asparaginase (AS, EC 6.3.5.4) and endopeptidase (EP, EC 3.4.24.11), especially after long-term soil drought. Plant biomass, leaf-biomass ratio between the green leaf and total plant biomass, net photosynthetic rate, stomatal conductance, the maximal efficiency of PSII photochemistry, the actual quantum yield, and the photochemical quenching were significantly reduced by severe water stress. Plant malondialdehyde (MDA) concentration increased with the increase in water stress, particularly at the late-growth stage. Our results suggest that the key enzymes of nitrogen metabolism may play an important role in the photosynthetic acclimation of L. chinensis plants to long-term soil drought.     

Hexavalent chromate reduction by alkaliphilic Amphibacillus sp. KSUCr3 is mediated by copper-dependent membrane-associated Cr(VI) reductase

The present study was aimed to localize and characterize hexavalent chromate [Cr(VI)] reductase activity of the extreme alkaliphilic Amphibacillus sp. KSUCr3 (optimal growth pH 10.5). The resting cells were able to reduce about 62 % of the toxic heavy metal Cr(VI) at initial concentration of 200 μM within 30 min. Cell permeabilization resulted in decrease of Cr(VI) reduction in comparison to untreated cells. Enzymatic assays of different sub-cellular fractions of Amphibacillus sp. KSUCr3 demonstrated that the Cr(VI) reductase was mainly associated with the membranous fraction and expressed constitutively. In vitro studies of the crude enzyme indicated that copper ion was essential for Cr(VI) reductase activity. In addition, Ca2? and Mn2? slightly stimulated the chromate reductase activity. Glucose was the best external electron donor, showing enhancement of the enzyme activity by about 3.5-fold. The K (m) and V (max) determined for chromate reductase activity in the membranous fraction were 23.8 μM Cr(VI) and 72 μmol/min/mg of protein, respectively. Cr(VI) reductase activity was maximum at 40 °C and pH 7.0 and it was significantly inhibited in the presence of disulfide reducers (2-mercaptoethanol), ion chelating agent (EDTA), and respiratory inhibitors (CN and Azide). Complete reduction of 100 and 200 μM of Cr(VI) by membrane associated enzyme were observed within 40 and 180 min, respectively. However, it should be noted that biochemical characterization has been done with crude enzyme only, and that final conclusion can only be drawn with the purified enzyme.     

Reduction of Hexavalent Chromium by Cell-Free Extract of Bacillus sphaericus AND 303 Isolated from Serpentine Soil

Cell-free extracts (CFEs) of chromium-resistant bacterium Bacillus sphaericus AND 303 isolated from serpentine soil of Andaman, India reduced Cr(VI) in in vitro condition, and the reductase activity was solely localized in the soluble cell-fractions (S₁₂, S₃₂, and S₁₅₀). The enzyme was constitutive as the CFEs from cells grown in Cr(VI)-free and Cr(VI)-containing media reduced a more or less equal amount of Cr(VI). Optimum Cr(VI) reductase activity was obtained at an enzyme (S₁₅₀) concentration equivalent to 4.56 mg protein/mL, 300 μM Cr(VI) and pH 6.0 after 30 min incubation at 30°C. The enzyme was heat labile; 80% of its activity was lost when exposed at 70°C for 15 min. Kinetics of Cr(VI) reductase activity fit well with the linearized Lineweaver-Burk plot and showed a V_max of 1.432 μmol Cr(VI)/mg protein/min and K_m of 158.12 μM Cr(VI). The presence of additional electron donors accelerated Cr(VI) reductase activity of CFE, and an increase of 28% activity over control was recorded with 1.0 μM NADH. Heavy metal ions such as Ni(II), Cu(II), and Cd(II) were strong inhibitors of Cr(VI) reductase unlike that of 100 μM Co(II), which retained 93% activity over control.     

微生物亚硝酸盐还原酶的研究进展

亚硝酸盐还原酶(Nitrite reductase,简称NiR,EC1.7.2.1)是催化亚硝酸盐(Nitrite,简称NIT)还原的一类酶,可降解NIT为NO或NH3,是自然界氮循环过程的关键酶。本文详细阐述亚硝酸盐还原酶的分类、结构特点、催化机制以及现阶段的应用领域,为深入研究亚硝酸还原酶提供参考。