不同栽培模式对冬小麦-夏玉米轮作系统产量、氮素累积和平衡的影响

以河北山前平原区秸秆还田条件下小麦-玉米轮作体系为研究对象,设置农民习惯、高产高效、再高产和再高产高效4个模式,通过定位试验探讨各栽培模式对3个轮作周期作物产量、土壤硝态氮累积量及氮平衡的影响.结果表明: 小麦、玉米产量均以再高产模式最高,高产高效和再高产高效模式次之,均显著高于农民习惯模式;小麦季和玉米季氮肥利用效率(PFP)均以高产高效模式最高,显著高于其他模式;0～400 cm土体硝态氮累积量在 768.4～1133.3 kg·hm^-2之间,其中80%～85%累积在根下90～400 cm土层;4种模式的土壤硝态氮均有明显向下淋移现象,120～150 cm和270～330 cm处均出现了累积峰,以270～330 cm土层硝态氮累积量最大;高产高效模式的土壤硝态氮含量整体水平均低于其他模式,浓度基本维持在30 mg·kg^-1以下,在一定程度上能有效缓解环境压力;冬小麦季0～90 cm土体氮素盈余量均小于夏玉米季,并以高产高效模式的氮素表观损失量最低,显著低于其他模式.综合考虑产量、氮肥利用效率、硝态氮累积和氮平衡,以高产高效模式表现最优,但还有一定的提升空间.     

膜下分区交替滴灌和施氮对棉花干物质累积与氮肥利用的影响

设置高水(260 mm)、中水(200 mm)、低水(140 mm)3水平的灌水量和高氮(270 kg·hm^-2)、中氮(180 kg·hm^-2)、低氮(90 kg·hm^-2)3水平的施氮量,进行完全组合设计,研究膜下分区交替滴灌和施氮对棉花干物质累积与氮肥利用的影响.结果表明：膜下分区交替滴灌棉花干物质量在中氮高水和高氮高水处理最高;与高氮高水处理相比,中氮高水处理干物质累积的施氮利用效率提高了34.0%～ 44.6%（平均提高34.7%）,灌水利用效率降低了6.4%～10.7%（平均降低10.2%）.对于棉花氮素累积,中氮高水处理的的施氮利用效率最高,高氮中水处理的灌水利用效率最高;与高氮中水处理相比,中氮高水处理的施氮利用效率提高了29.0%～41.7%,灌水利用效率下降了5.5%～14.0%.在棉花产量较高的水氮耦合处理中,中氮高水处理的棉花氮回收率、氮肥农学利用效率和表观利用效率均高于高氮中水和高氮高水处理,而氮肥吸收比例和氮肥生理利用效率无显著差异.表明中氮高水处理最有利于膜下分区交替滴灌水氮耦合效应的发挥.     

Pyridoxine and atherosclerosis: role of pyridoxine in the metabolism of lipids and glycosaminoglycans in rats fed normal and high fat, high cholesterol diets containing 16% casein

The effect of administration of low and high doses of pyridoxine on the metabolism of lipids and glycosaminoglycans has been studied in rats fed normal and high fat, high cholesterol diets. Low doses of pyridoxine (0.005 mg/100 g body weight) caused increased concentrations, of cholesterol and triglycerides in the serum and aorta in animals fed normal and high fat, high cholesterol diets. Administration of high doses of pyridoxine (5.0 mg/100 g body weight) caused decrease in the concentration of these lipids in these tissues except in the case of the aorta in the animals fed a normal diet. Low doses of pyridoxine generally caused a decrease in the concentration of many glycosaminoglycan fractions in the aorta in rats fed normal and high fat, high cholesterol diets, whilst high doses caused an increase. The activity of glucosaminephosphate isomerase (glutamine-forming) and UDPglucose dehydrogenase, both key enzymes in the biosynthetic pathway of glycosaminoglycans, decreased in rats given low doses of pyridoxine and increased in rats given high doses. The activity of many enzymes concerned with degradation of glycosaminoglycans--hyaluronoglucosidase, beta-glucuronidase, beta-N-acetylglucosaminidase, aryl sulphatase, and cathepsin D--generally increased in rats fed low doses of the pyridoxine and decreased in those given high doses. The concentration of hepatic 3'-phosphoadenosine-5'-phosphosulphate, and the activity of the sulphate-activating system and of aryl sulphotransferase decreased when the dose of pyridoxine was low and increased when the dose was high.     

Growth Kinetics, Carbohydrate, and Leaf Phosphate Content of Clover (Trifolium subterraneum L.) after Transfer to a High CO(2) Atmosphere or to High Light and Ambient Air

Intact air-grown (photosynthetic photon flux density, 400 microeinsteins per square meter per second) clover plants (Trifolium subterraneum L.) were transfered to high CO₂ (4000 microliters CO₂ per liter; photosynthetic photon flux density, 400 microeinsteins per square meter per second) or to high light (340 microliters CO₂ per liter; photosynthetic photon flux density, 800 microeinsteins per square meter per second) to similarly stimulate photosynthetic net CO₂ uptake. The daily increment of net CO₂ uptake declined transiently in high CO₂, but not in high light, below the values in air/standard light. After about 3 days in high CO₂, the daily increment of net CO₂ uptake increased but did not reach the high light values. Nightly CO₂ release increased immediately in high light, whereas there was a 3-day lag phase in high CO₂. During this time, starch accumulated to a high level, and leaf deterioration was observed only in high CO₂. After 12 days, starch was two- to threefold higher in high CO₂ than in high light, whereas sucrose was similar. Leaf carbohydrates were determined during the first and fourth day in high CO₂. Starch increased rapidly throughout the day. Early in the day, sucrose was low and similar in high CO₂ and ambient air (same light). Later, sucrose increased considerably in high CO₂. The findings that (a) much more photosynthetic carbon was partitioned into the leaf starch pool in high CO₂ than in high light, although net CO₂ uptake was similar, and that (b) rapid starch formation occurred in high CO₂ even when leaf sucrose was only slightly elevated suggest that low sink capacity was not the main constraint in high CO₂. It is proposed that carbon partitioning between starch (chloroplast) and sucrose (cytosol) was perturbed by high CO₂ because of the lack of photorespiration. Total phosphate pools were determined in leaves. Concentrations based on fresh weight of orthophosphate, soluble esterified phosphate, and total phosphate markedly declined during 13 days of exposure of the plants to high CO₂ but changed little in high light/ambient air. During this time, the ratio of orthophosphate to soluble esterified phosphate decreased considerably in high CO₂ and increased slightly in high light/ambient air. It appears that phosphate uptake and growth were similarly stimulated by high light, whereas the coordination was weak in high CO₂.     

影响二花脸猪高产仔性能的生理及遗传机制研究进展

二花脸猪是我国太湖流域以产仔数高而闻名于世界的优质猪种。已有的研究发现,二花脸猪排卵数高、胚胎死亡率低和子宫容积大是其高产性能的重要生理特征,通过候选基因法鉴别到其高产的重要候选基因——促卵泡素β亚基(follicular-stimulating hormone beta, FSH?),采用QTL定位方法在猪第2、6、7、8、12、13和15号染色体上定位到影响其产仔性状的QTL。但是,目前影响二花脸猪产仔数的主效基因尚不清楚。本文主要介绍了二花脸猪的高排卵数、低胚胎死亡率和高子宫容积特性对高产仔性能形成的生理作用;概括了基于传统方法鉴别出的影响二花脸猪高产仔性能的候选基因和QTL,以及基于组学方法鉴别出的二花脸猪高产候选基因;探讨了如何利用基因组、转录组、蛋白质组和功能组等多组学手段深入研究二花脸猪高产性能的成因,以期为深入解析二花脸猪高产性能的分子遗传机制提供参考。     

Rat plasma high-molecular-weight kininogen. A simple method for purification and its characterization

High-molecular-weight kininogen has been isolated from rat plasma in three steps in a relatively high yield. The purified preparation gave a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the absence and presence of 2-mercaptoethanol, and the apparent Mr was estimated as 100,000. On incubation with rat plasma kallikrein, rat high Mr kininogen yielded a kinin-free protein consisting of a heavy chain (Mr = 64,000) and a light chain (Mr = 46,000), liberating bradykinin. The kinin-free protein was S-alkylated, and its heavy and light chains were separated by a zinc-chelating Sepharose 6B column. The amino acid compositions of rat high Mr kininogen and its heavy and light chains were very similar to those of bovine high Mr kininogen and its heavy and fragment 1.2-light chains, respectively. A high histidine content in the light chain of rat high Mr kininogen indicated the presence of a histidine-rich region in this protein as in bovine high Mr kininogen, although this region was not cleaved by rat plasma kallikrein. Rat high Mr kininogen corrected to normal values the prolonged activated partial thromboplastin time of Brown-Norway Katholiek rat plasma known to be deficient in high Mr kininogen and of Fitzgerald trait plasma. The kinin-free protein had the same correcting activity as intact high Mr kininogen. Rat high Mr kininogen also accelerated approximately 10-fold the surface-dependent activation of rat factor XII and prekallikrein, which was mediated with kaolin, amylose sulfate, and sulfatide. These results indicate that rat high Mr kininogen is quite similar to human and bovine high Mr kininogens in terms of biochemical and functional properties.     

灌浆期高温对水稻光合特性、内源激素和稻米品质的影响

以2个籼稻品种:温度钝感型品种K30和温度敏感型品种R21为材料,利用人工气候室控温,在水稻灌浆期设置高温(日均温度34.9℃)和适温(日均温度28.0℃)处理,测定不同灌浆时期(5,10,15,20,25d和30d)光合特性、内源激素含量及稻米品质的变化。结果表明,高温增强了K30的光合能力,K30高温处理净光合速率(Pn)在整个灌浆期都明显高于对照;R21在灌浆前期(5、10d和15d)高温处理与适温处理Pn差异不明显,在灌浆后期(20、25d和30d)高温处理Pn下降。高温增加了K30叶片和籽粒脱落酸(ABA)含量;而R21高温处理和适温处理叶片与籽粒ABA含量的对比不明显。高温处理对两个水稻品种叶片和籽粒赤霉素(GA3)与生长素(IAA)含量也有不同程度影响。高温胁迫降低稻米品质,但K30比R21表现出更强的温度钝感特性。     

氮磷水平对龙须菜生长和光合特性的影响

研究不同营养盐条件对龙须菜(Gracilaria lemaneiformis)的生理效应, 对深入了解龙须菜与近海环境的相互作用具有重要意义。在低氮低磷(LNLP)、低氮高磷(LNHP)、高氮低磷(HNLP)和高氮高磷(HNHP) 4种营养盐条件下培养龙须菜15 d, 以探讨不同氮、磷水平对龙须菜生长和光合特性的影响。结果表明: 1) LNHP、HNLP和HNHP处理促进了龙须菜的生长, 其中HNHP处理下龙须菜具有最大的相对生长速率和生物量; 2) LNHP、HNLP和HNHP处理提高了龙须菜的光合无机碳利用能力, 其中HNHP处理下龙须菜具有最大的无机碳饱和光合速率和表观半饱和常数, 比LNLP处理分别提高了118%倍和48.71%; 3) LNHP、HNLP和HNHP处理显著影响龙须菜的光化学效率, 与LNLP处理相比, LNHP处理提高了龙须菜的光化学效率, 而HNLP和HNHP处理降低了龙须菜的光化学效率。研究结果表明, HNHP处理条件下, 龙须菜的生长和光合无机碳利用能力最高, 光化学效率最低。     

波动性高糖对肾小管上皮细胞Wnt／β-catenin信号途径的影响

肾脏纤维化分为肾小球硬化和肾小管间质纤维化（tubular interstitial fibrosis,TIF）,而TIF过程与肾损伤具有密切的关系。TIF是由于细胞外基质的过度沉积造成的,肌成纤维细胞是TIF发生发展过程中产生细胞外基质的主要细胞,该过程被成纤维细胞激活,涉及上皮细胞向肌成纤维细胞的转分化^[1-2]。Wnt／β-catenin信号途径涉及细胞增殖、肿瘤发生与转移的调控。β-catenin是Wnt信号途径的关键分子,在细胞的生长与分化过程中起着重要的作用,     

白藜芦醇甙减轻高糖所致心肌微血管内皮细胞损伤的作用及机制研究

目的:探讨白藜芦醇甙在高糖处理的大鼠心肌微血管内皮细胞损伤中的作用及其可能调控机制。方法:酶消法分离大鼠CMECs,高糖处理CMECs建立细胞损伤模型,实验随机分为6个组:对照组(葡萄糖浓度为5.5 mmol/L)、白藜芦醇甙组、高糖组(葡萄糖浓度为33 mmol/L)、高糖+白藜芦醇甙组、高糖+白藜芦醇甙+3-MA(自噬抑制剂)组和高糖+雷帕霉素(自噬诱导剂)组。白藜芦醇甙组和高糖+白藜芦醇甙组分别加入10μmol/L的白藜芦醇甙孵育24 h,高糖+白藜芦醇甙+3-MA组加入10μmol/L的白藜芦醇甙和10μmmol/L 3-MA孵育24 h,高糖+雷帕霉素组加入100 nmol/L的雷帕霉素孵育24小时。CCK-8实验检测大鼠CMECs增殖;Tunel法检测大鼠CMECs凋亡;FITC-葡聚糖清除实验检测单层CMECs通透性;Western blot检测LC3Ⅱ和p62的表达。结果:与对照组和白藜芦醇甙组相比,高糖组CMECs增殖能力降低(P<0.05),凋亡率显著增加(P<0.05),细胞通透性增加(P<0.05),LC3Ⅱ表达降低(P<0.05),p62的表达增加(P<0.05);与高糖组相比,高糖+白藜芦醇甙组和高糖+雷帕霉素组CMECs增殖能力增加(P<0.05),凋亡率显著降低(P<0.05),细胞通透性降低(P<0.05),LC3Ⅱ表达增加(P<0.05),p62的表达降低(P<0.05);与高糖+白藜芦醇甙组相比,高糖+白藜芦醇甙+3-MA组CMECs增殖能力降低(P<0.05),凋亡率显著增加(P<0.05),细胞通透性增加(P<0.05),LC3Ⅱ表达降低(P<0.05),p62的表达增加(P<0.05)。结论:白藜芦醇甙通过增加自噬减轻高糖处理的大鼠心肌微血管内皮细胞损伤。     

Electrical activity of the amygdala and the septum of rats on a high fat or a high protein diet

The authors studied biopotentials in the region of the amygdala and the septum of rats fed on a standard, high protein or high fat diet. During the first 3-6 days after changing from the standard to the high protein or high fat diet, a decrease in the amplitude of electrical activity was found in both the regions in question. After 3 days on the high fat or the high protein diet, an increase was found in the frequency of electrical activity in the amygdala or the septum, according to the type of diet. A study of the amplitude of electrical activity showed that the electrical potential in the septum was always lower than in the amygdala. The frequency spectrum analysis showed a marked change in the superimposed frequency curve only in animals fed on the high fat diet.     

高温对环带锦斑蛾幼虫滞育的抑制作用

本文报道了高温（31℃）对环带锦斑蛾幼虫滞育发生的抑制作用。当幼虫暴露于31℃ 时,所有个体都继续发育,与光周期无关。在诱导滞育的光周期条件(L12∶D12)下,光期的高温配合不同的暗期低温（15～28℃）,导致几乎所有个体滞育,但当暗期为5℃时,滞育率反而下降;相反,当光期的低温配合不同持续时间的暗期高温（31℃）时,则几乎所有的个体都继续发育,这说明高温在暗期发挥着重要的作用。在暗期给予不同时间长度（2、4、 6、8、10、12 h）的高温处理,结果表明一个2 h的高温处理就能有效地抑制滞育的发生。在暗期的不同时间给予4 h高温处理,显示了幼虫在暗期开始后的第一个4 h (18:00～22:00 )对高温最敏感,完全抑制了滞育的发生。最后讨论了高温调节滞育机制在该虫生活史上的适应意义。     

猪骨胶原蛋白肽缓解高脂饮食诱导小鼠肝脏氧化应激的基因芯片分析

本研究探讨猪骨胶原蛋白肽降血脂作用和抑制高脂饮食诱导肝脏抗氧化应激的作用机理。40只小鼠分为5组,分别饲喂6 w正常日粮、高脂日粮、添加1.6%钙的高脂日粮、添加1%胶原蛋白肽的高脂日粮和添加1.6%钙+1%胶原蛋白肽的高脂日粮。研究发现:与正常组相比,高脂日粮小鼠血脂和体重明显升高。1.6%钙处理可抑制体重过度升高,1%胶原蛋白肽和高钙可协同抑制调节血脂,防止体重升高。高脂主要通过影响肝脏生理节律和过氧化物酶体增生物激活受体信号通路引起脂代谢异常,高钙和骨胶原蛋白肽可显著抑制肝脏氧化应激,抑制生理节律紊乱。     

Isoform-specific induction of PKC-epsilon by high glucose protects heart-derived H9c2 cells against hypoxic injury

We investigated which PKC isoforms are involved in high glucose-induced protection against hypoxic injury. Treatment for 48 h with high glucose (22 mM) markedly increased the expression of PKC- epsilon in the particulate fraction (213+/-22.1% of the control) but had no effect on other types of PKC isoforms, suggesting that the high glucose-induced increase in PKC expression is isoform-specific. The mRNA level for PKC- epsilon was also substantially increased, reaching its peak after 4h of high glucose treatment. The high glucose increased PKC-epsilon activity in the particulate fraction up to 183+/-32.2% of the control. During hypoxia, the amount of PKC-epsilon in the particulate fraction was remarkably diminished in the low glucose-treated cells, but remained at a higher level in high glucose-treated cells. The treatment with epsilon V1-2 (10 microM), a specific inhibitor of PKC epsilon, abolished the protective effect of high glucose against hypoxia. These results suggest that isoform-specific induction of PKC-epsilon is involved in high glucose-induced protection against hypoxic injury in heart-derived H9c2 cells.     

Role of Glucose-6-phosphatase in Hepatic and Renal Gluconeogenesis

Comparison of the effects of a high fat and high protein diet on the capacity for glucose formation from pyruvate and glycerol was investigated in vivo and in vitro. Ratios of radioactivity incorporated from either pyruvate-3-¹⁴C or glycerol-l-¹⁴C into blood glucose to those into expired CO₂ were higher in both groups fed the high fat and the high protein diet than those in a group fed a high carbohydrate diet. Gluconeogenesis from pyruvate and glycerol by liver slices were both increased significantly in rats fed the high fat diet, while feeding the high protein diet caused increase of renal gluconeogenesis from pyruvate and glycerol. The activities of hepatic and renal glucose-6-phosphatase(s) were changed in a similar fashion to changes in hepatic and renal gluconeogenesis, respectively.

In addition, the response of the activity of hepatic glucose-6-phosphatase with high dietary fat was more rapid than that of the activity of renal glucose-6-phosphatase with high dietary protein. Furthermore, the intraperitoneal injection of actinomycin-D to rats resulted in decrease of the activities of renal glucose-6-phosphatase of both groups fed the high fat and the high protein diet, but no significant change of the activity of hepatic glucose-6-phosphatase was observed among dietary groups.

These findings suggested that the increases in the overall flow of metabolites towards glucose formation by feeding the high fat and the high protein diet might be based on the action of different mechanisms which regulate the activities of glucose-6-phosphatase(s) of the liver and kidney.     

High Light-Induced Unstacking of Thylakoids and Randomization of Pigment-Protein Complexes of Chloroplast

Using absorbance changes at 540 nm and the per cent chlorophyll in 10K pellet after digitonin fractionation as the criteria of thylakoid stacking, high light induced unstacking of thylakoids and randomization of pigment protein complexes of chloroplast was characterized. Cation-induced increase in absorbance at 540 nm was abolished when chloroplasts were exposed to high light. Also, the high light induced decrease in absorbance at 540 nm was more pronounced In low salt chloroplasts as compared to the decrease in 540 nm absorbance in chloroplasts isolated in high salt. The decrease In the fraction of chlorophyll in digitonin fractionated 10K pellet was much more than the decrease in chlorophyll in 10K pellet from high salt chloroplasts exposed to high light These results suggest that high light causes unstacking of thylakoids.     

Accumulation of calcium, potassium and magnesium in apple fruits under various conditions of humidity

In each of two experiments done under controlled conditions, starting at bloom, 4 humidity treatments were applied to potted trees of apple ( Malus pumila Mill. cv. Cox's Orange Pippin), i. e. in experiment 1: (1) high humidity throughout, (2) low humidity throughout, (3) low humidity for 7 weeks followed by high humidity for 6-7 weeks, and (4) the reverse (first high and then low humidity); in experiment 2: (1) day/night humidity high/high, (2) low/low, (3) low/high, and (4) high/low.
In both experiments high humidity favoured shoot growth appreciably. Change from low to high humidity after 7 weeks resulted in some growth stimulation but in the reverse situation growth was markedly reduced. Shoot growth responded little to different night humidities. In the two experiments fruit growth was little affected by treatments. In experiment 2 irrespective of night humidity, water consumption was higher at low than at high day humidity. In the high/low humidity regime water use during the night was high and leaf water potential low, relatively; during the day water potential was little affected by treatments.
At any time leaf Ca and Mg were clearly highest at low day humidity; night humidity had no effect. Leaf K did not respond to treatments. Fruit Ca at high humidity throughout was lower than at low humidity throughout. Increasing humidity later in the season was ineffective but a decrease at that time tended to reduce fruit Ca slightly. The clearly lowest Ca values occurred in the high/low day/night treatment. Fruit K and Mg were not or hardly affected by treatments.
The findings are discussed in terms of humidity effects on transpiration, shoot and fruit growth, and xylem mineral concentration and ion exchange translocation along the xylem walls.     

Polyethylene glycol-modified GM-CSF expands CD11b(high)CD11c(high) but notCD11b(low)CD11c(high) murine dendritic cells in vivo: a comparative analysis with Flt3 ligand

Dendritic cells (DC) are potent APCs that can be characterized in the murine spleen as CD11b(high)CD11c(high) or CD11b(low)CD11c(high). Daily injection of mice of Flt3 ligand (FL) into mice transiently expands both subsets of DC in vivo, but the effect of administration of GM-CSF on the expansion of DC in vivo is not well defined. To gain further insight into the role of GM-CSF in DC development and function in vivo, we treated mice with polyethylene glycol-modified GM-CSF (pGM-CSF) which has an increased half-life in vivo. Administration of pGM-CSF to mice for 5 days led to a 5- to 10-fold expansion of CD11b(high)CD11c(high) but not CD11b(low)CD11c(high) DC. DC from pGM-CSF-treated mice captured and processed Ag more efficiently than DC from FL-treated mice. Although both FL- and pGM-CSF-generated CD11b(high)CD11c(high) DC were CD8alpha-, a greater proportion of these DC from pGM-CSF-treated mice were 33D1+ than from FL-treated mice. CD11b(low)CD11c(high) DC from FL-treated mice expressed high levels of intracellular MHC class II. DC from both pGM-CSF- and FL-treated mice expressed high levels of surface class II, low levels of the costimulatory molecules CD40, CD80, and CD86 and were equally efficient at stimulating allogeneic and Ag-specific T cell proliferation in vitro. The data demonstrate that treatment with pGM-CSF in vivo preferentially expands CD11b(high)CD11c(high) DC that share phenotypic and functional characteristics with FL-generated CD11b(high)CD11c(high) DC but can be distinguished from FL-generated DC on the basis of Ag capture and surface expression of 33D1.     

Developmental,genetic, and environmental components of aerobic capacity at high altitude

The aerobic capacity of 268 subjects (158 males and 110 females) was evaluated in La Paz, Bolivia situated at 3,750 m. The sample included 1) 39 high altitude rural natives (all male); 2) 67 high altitude urban natives (32 male, 35 female); 3) 69 Bolivians of foreign ancestry acclimatized to high altitude since birth (37 male, 32 female); 4) 50 Bolivians of foreign ancestry acclimatized to high altitude during growth (25 male, 25 female); and 5) 43 non-Bolivians of either European or North American ancestry acclimatized to high altitude during adulthood (25 male, 18 female). Data analyses indicate that 1) high altitude urban natives, acclimatized to high altitude since birth or during growth, attained higher aerobic capacity than subjects acclimatized to high altitude during adulthood; 2) age at arrival to high altitude is inversely related to maximum oxygen consumption (V?O² max) expressed in terms L/min or ml/min/kg of lean body mass, but not in terms of ml/min/kg of body weight; 3) among subjects acclimatized to high altitude during growth, approximately 25% of the variability in aerobic capacity can be explained by developmental factors; 4) as inferred from evaluations of skin color reflectance and sibling similarities, approximately 20 to 25% of the variability in aerobic capacity at high altitude can be explained by genetic factors; 5) except among the non-Bolivians acclimatized to high altitude during adulthood, the aerobic capacity of individuals with high occupational activity level is equal to the aerobic capacity of high altitude rural natives; and 6) the relationship between occupational activity level and aerobic capacity is much greater among subjects acclimatized to high altitude before the age of 10 years than afterwards. Together these data suggest that the attainment of normal aerobic capacity at high altitude is related to both developmental acclimatization and genetic factors but its expression is highly mediated by environmental factors, such as occupational activity level and body composition. © 1995 Wiley-Liss, Inc.     

Inhibition of ammonium assimilation restores elongation of seminal rice roots repressed by high levels of exogenous ammonium

Elongation of seminal and lateral roots of rice seedlings was markedly inhibited by high ammonium levels in growth medium. However, high exogenous nitrate concentrations had little inhibitory effect on root growth. The objective of this study was to elucidate the relationship between inhibition of rice root growth induced by high ammonium conditions and ammonium assimilation in the seedlings. Activity of glutamine synthetase (GS) was kept at a low level in the seminal roots of the seedlings grown under high nitrate levels. In contrast, high ammonium levels significantly enhanced the GS activity in the roots, so that Gln abundantly accumulated in the shoots. These results indicate that ammonium assimilation may be activated in the seminal roots under high ammonium conditions. Application of methionine sulfoximine (MSO), an inhibitor of GS, relieved the repression of the seminal root elongation induced by high ammonium concentrations. However, the elongation of lateral roots remained inhibited even under the same condition. Furthermore, MSO drastically increased ammonium level and remarkably decreased Gln level in the shoots grown under high ammonium conditions. These results show that, for rice seedlings, an assimilatory product of ammonium, and not ammonium itself, may serve as an endogenous indicator of the nitrogen status involved in the inhibition of seminal root elongation induced by high levels of exogenous ammonium.