NO_3~-上运和液泡内NO_3~-外流对小麦叶内硝酸还原酶活性的调节

NO_3~-亏缺能使叶片硝酸还原酶活性(NRA)和NO_3~-总量降低,而根部NO_3~-吸收及上运能力提高,以亏缺2d的幼苗最为明显,该幼苗经12hNO_3~-吸收,叶片的NRA高于未经亏缺的幼苗,但NO_3~-含量以后者为高,代谢库中NO_3~-含量前者高于后者。提高营养液中NO_3~-浓度,NO_3~-上运速率升高,叶片内NRA增加。叶片组织暗中无氧保温40min后,代谢库体积渐大,液泡内NO_3~-有外流产生;Cl~-可促使液泡内NO_3~-外流,代谢库中NO_3~-量增加,NRA升高。NRA在体内测定条件下,保温3h后,NO_2~-产生趋于稳值,NRA降至最低;系统中加KCl或KNO_3使NO_2~-产生趋于稳值的时间延长,且能提高NO_2~-积累总量。     

微生物代谢产物库研究进展

微生物代谢物具有极大的化学结构多样性和复杂性,建立微生物代谢物库对发现新药有重要意义。对几种重要的微生物代谢物库及建库方法作一综述。     

亚硫酸盐对小麦幼苗叶组织生长代谢的影响

在低浓度亚硫酸盐作用下,小麦幼苗叶片中超氧化物歧化酶（SOD）和过氧化物酶（POD）活性升高;随着亚硫酸盐浓度的增加,叶片的叶绿素含量下降,游离脯氨酸和脂质过氧化产物丙二醛（MDA）含量增加,SOD活性下降,POD活性显著升高。研究表明,高浓度的亚硫酸盐对植物生长有抑制和毒害作用。     

MDMPR:小鼠发育代谢表型库

小鼠发育代谢表型库(Mouse Developmental and Metabolic Phenotype Repository,MDMPR)是一个致力于小鼠资源和表型数据实时共享的开放性平台,它依托于科技部重点研发计划“发育编程及其代谢调节”专项项目“建立小鼠发育代谢表型库”。该项目预计在5年内完成500个发育代谢相关小鼠敲除模型的建立,并对其表型数据进行标准化的解析、建立表型数据库。MDMPR作为一个资源及数据集成的库,由多个子系统作为支撑,包括ES细胞数据库、项目管理系统、繁育管理系统、精子库管理系统、表型分析系统,信息化管理深入到项目中每个环节,从基因突变ES细胞制备、基因突变小鼠制备、小鼠繁育,精子冻存到最终的表型分析、数据处理及展示,保证了MDMPR产生数据的真实性及实时性。MDMPR除了不断地推进项目进行,增加自身产生的数据外,也在积极的整合其他的资源及数据,如人特异性基因敲除ES细胞库、蛋白相互作用数据库(STRING)、核心转录调节环路(dbCoRc)和Enhancer-Indel数据库,今后还将进一步整合,帮助发育代谢及其他领域的研究人员能够一站式的获取所需资源和数据、加快研究进程,最终服务于全人类的医疗事业。     

不同穗型小麦品种分蘖发育的代谢基础研究

比较研究了大穗型和多穗型小麦品种的分薛发育特征及其代谢基础。结果表明,与多穗型品种相比,单株分蘖较少的大穗型品种分蘖期具有较低的IAA氧化酶（IAAO）活性、较高的IAA含量和较强的碳代谢活性。在分蘖的两极分化期,大穗型品种在碳、氮代谢和同化物分配方面存在较强的主茎优势,因此,其分蘖较难继续发育成穗。     

外源钙离子对小麦幼苗氮素代谢的影响

以普通小麦豫麦34为材料,研究了不同浓度的外源Ca2 对小麦幼苗氮素代谢的影响.在小麦第一片叶完全展开后,开始外源Ca2 处理,设0 (对照)、2、4 mmol · L-1 和8 mmol · L-1 4个Ca2 浓度梯度.处理5d后,测定氮同化酶活性、氮同化量及其它相关代谢物含量.结果表明,小麦幼苗叶片中硝酸还原酶(NR)和谷氨酰胺合成酶(GS)在2 mmol · L-1 Ca2 处理下活性比对照有显著增加,4 mmol · L-1 Ca2 处理的NR活性增加明显,但GS活性增加不显著;8 mmol · L-1 Ca2 处理下NR和GS活性比对照均明显降低.谷氨酸脱氢酶(NADH-GDH)活性在2 mmol · L-1 Ca2 处理下活性增加不明显,而在4、8 mmol · L-1 Ca2 处理下活性显著增加.小麦幼苗氮同化量以4 mmol · L-1处理最大,2 mmol · L-1处理与4 mmol · L-1之间差异不显著;Ca2 浓度为8 mmol · L-1时,氮素同化量明显降低.结果揭示了小麦幼苗不同氮同化途径对Ca2 的响应不同,GS途径比GDH途径对小麦氮素同化量的增加作用更大;4 mmol · L-1对小麦幼苗的氮素利用可能是最有效的Ca2 浓度.     

汞对小麦种子活力和萌发代谢的影响

研究Ｈｇ＾２＋对小麦种子活力、幼苗生长、呼吸及淀粉酶、脂肪酶和转氨酶活力的影响。结果表明,Ｈｇ＾２＋能抑制种子萌发过程中淀粉酶、脂肪酶和转氨酶活性,抑制幼苗生长和呼吸代谢,降低种子活力,但浓度低时,在萌发初期有短暂促进作用。     

菠菜叶片中硝态氮还原与叶柄中硝态氮累积的关系

测定了不同生长期在不同施氮水平下3个菠菜品种各器官的硝态氮含量、叶片的硝酸还原酶活性、叶片细胞硝态氮的贮存库和代谢库大小.结果表明:叶柄中硝态氮含量远高于其它器官,其含量与叶片内源/外源硝酸还原酶活性的比值呈负相关;叶片细胞中硝态氮代谢库的大小与叶柄中硝态氮含量之间没有确定的关系.     

Saturation and Utilization of Nitrate Pools in Pea and Sugar Beet Leaves

The critical periods in the saturation of pea and sugar beet leaves with nitrate absorbed by roots were discriminated. In peas, during the first 14 h, all nitrate penetrating leaf cells was concentrated in the cytosol (metabolic pool). During the second period (14–62 h), nitrate began to flow into the vacuole (storage pool), and the filling of the metabolic pool continued. Metabolic pool was saturated by the end of this period (62 h). During the third period (62–110 h), further nitrate accumulation in the cell occurred because of expanding of the storage pool. Its saturation (similarly as total cell saturation) commenced 86 h after the start of nitrate uptake. In sugar beet leaves, both metabolic and storage nitrate pools were saturated by the end of the first period (14 h), and the sizes of these pools did not change during the second period (14–86 h). When pea plants were transferred to the nitrate-free medium, nitrate efflux began from the storage pool until its complete exhausting after 3 days. In sugar beet leaves, nitrate was still present in the storage pool 4 days after plant transfer to the nitrate-free medium. In both crops, nitrate export from the storage pool was aimed at the maintenance of the optimum nitrate concentration in the metabolic pool and, thus, at the maintenance of nitrate reductase activity. A functional diversity of nitrate compartmentation in the cells of various plant species is discussed.     

菠菜叶片中硝态氮代谢库的测定（简报）

随着培养时间的延长 ,菠菜组织中还原产生的亚硝态氮量呈波动型上升 ;以 pH 7.5的磷酸缓冲液为培养介质的亚硝态氮累积量显著高于以KCl和CaCl2 混合溶液 ( pH 6.65 )为介质的 ;培养前不通氮气 ,培养后期亚硝态氮的生成量明显高于通氮气的。亚硝态氮生成第一峰值出现的时间随硝态氮含量增高而后延 ,峰值却随硝态氮含量的增高而升高。用 pH 7.5的 0 .0 5mol·L-1磷酸缓冲液且不通氮气对组织进行培养 ,亚硝态氮生成的第一个峰值代表硝态氮代谢库的大小。     

小麦开花后不同器官中硝酸还原酶和谷氨酰胺合成酶的活性比较

小麦开花后各器官的硝酸还原酶和谷氨酰胺合成酶均具有一定的活性,旗叶中硝酸还原酶和谷氨酰胺合成酶活性最高。开花后旗叶和根系硝酸还原酶和谷氨酰胺合成酶活性逐渐降低,颗壳和籽粒中硝酸还原酶和谷氨酰胺合成酶活性先升高,达到最大值后又降低。     

Role of Protein Synthesis in Recovering Nitrate Reductase Activity in Wheat Leaves Exposed to Heat Stress

Heating intact leaves of 14–15-day-old seedlings of wheat (Triticum aestivumL.), cv. Albidum 29, for 10 min at 44–45°C brought about a decrease in nitrate reductase activity by 50–90% of the initial level. The complete recovery of the enzyme activity occurred one to two days after the plants were returned to normal temperature conditions. Darkening plants or adding cycloheximide to the nutrient medium did not interfere with the recovery of nitrate reductase activity. The plants grown in darkness or on a nitrate-free medium were devoid of nitrate reductase activity. The transfer of these plants to the light or the addition of nitrate resulted in the induction of enzyme activity. In the untreated plants, nitrate reductase activity attained the control level in 48 h; in the heated plants, this process was considerably retarded. After heating, the activity of the preexisting enzyme recovered at a higher rate than the ability for enzyme induction. This means that the reactivation of nitrate reductase occurred even when the induction of the enzyme was almost entirely suppressed. We conclude that after the short-term effect of high temperatures, the functional activity of nitrate reductase may recover without the de novosynthesis of the enzyme protein.     

Heat-Induced Increase in the Stability of Nitrate Reductase from Wheat Leaves against Inactivating Factors

Heating of wheat seedlings (Triticum aestivum L.) for 3 h at 41–42°C (heat hardening) increased the thermal stability of nitrate reductase (NR). After transferring hardened plants to normal temperature, the higher level of thermal stability persisted for 6 days. The heat hardening increased the enzyme stability against the proteolytic effect of trypsin and reduced the rate of NR degradation in extracts. Inhibition of the NR synthesis by transferring plants to a nitrate-free medium resulted in a much lower rate of enzyme degradation in the cells of hardened, as compared to unhardened plants. A short-term heating of seedlings (10 min at 36, 40, and 44°C) increased the ability of NR to reactivate after heat damage. The thermal stability of NR increased only in seedlings that had been hardened at 40 and 44°C, whereas hardening at 36°C did not result in enzyme stabilization. It is concluded that heat hardening (hyperthermia) increases NR stability against a number of inactivating factors (heating, proteolysis,in vitroand in vivo enzyme degradation) and enhances its ability to repair damage induced by heating.     

Effect of Elevated Temperature on Nitrite and Nitrate Reduction in Leaves and Intact Chloroplasts

Barley (Hordeum vulgare L.) leaves and intact spinach (Spinacia oleracea L.) chloroplasts were exposed to short-term heating, and the aftereffects of heat treatment on in vitro andin vivo activities of nitrate reductase and noncyclic electron transport associated with nitrite reduction were studied. Heating of leaves at temperatures above 40°C led to a monotonic decrease in nitrate reductase in vitro activity. On the contrary, the in vivo enzyme activity, assayed in intact leaf tissues after 5-min heat treatment, increased 1.5 times upon elevating the pretreatment temperature from 37 to 40°C and gradually decreased at higher temperatures. Noncyclic electron transport related to CO₂ fixation in intact chloroplasts decreased gradually after heat exposures above 39°C, unlike the electron transport to nitrite as a terminal acceptor, which was stimulated by heating of intact chloroplast suspensions in the temperature range from 33 to 40°C. The heating at higher temperatures inhibited nitrite photoreduction. It is concluded that the heating of phototrophic cells at sublethal temperatures stimulates the mobilization of inorganic nitrogen and thereby facilitates the repair of thermally induced injuries of proteinaceous cell structures. The stimulation of nitrate reductase activity in vivo at the temperature range 37–40°C provides an evidence for the increase in the availability of reductants in the cytosolic compartment of the leaf cell.     

玉米幼苗NO_3~-的吸收、溢泌和硝酸还原酶活性在品种间的差异

玉米品种间NO_3~-吸收的表观米氏常数(K_m,app)、最大吸收速率(I_m)有明显的差异。品种813NO_3~-吸收速率大于中单2号;溢泌液体积及其NO_3~-含量也是这样。硝酸还原酶(NR)的体外测定表明,地上部的活性比根部的大得多;不论地上部或根部的NR活性(NRA),品种813的大于中单2号。NRA的体内测定表明,去胚乳和盾片的幼苗经诱导,反应液有NO_3~-,813的第1叶的NRA大于中单2号;不去胚乳和盾片幼苗的第1叶NRA中单2号大于813。     

Effects of Energy Substrates on Nitrate Reduction and Nitrate Reductase Activity in a Ruminal Bacterium, Selenomonas ruminantium

The factors affecting the rate of nitrate reduction and the nitrate reductase content in Selenomonas ruminantium were examined. The rate of nitrate reduction per cell mass was higher when S. ruminantium was grown on lactate than when grown on glucose, and the rate was further enhanced when grown on succinate. The nitrate reduction rate was parallel to the nitrate reductase content in cells, suggesting that the amount of nitrate reductase limits the rate of nitrate reduction. The amount of nitrate reductase was inversely related to growth rate. The growth rate was related to the level of intracellular ATP, which was inversely related to the levels of ADP and AMP. The ratio of NADH to NAD⁺was related to the rate of nitrate reduction and to the amount of nitrate reductase. From these results, it is conceivable that the synthesis of nitrate reductase is regulated in response to the sufficiency of energy and electron supply. Intracellular concentrations of adenine nucleotides and pyridine nucleotides may be the regulating factors. The amount of nitrate reductase was increased by the presence of nitrate, suggesting that the synthesis of nitrate reductase is enhanced by nitrate. In addition, nitrate reduction altered the fermentation pattern as a result of electron consumption.