In Vivo Methylation of an Arginine in Chicken Myelin Basic Protein

Abstract: The amino acid sequence around the sole methylarginine residue in chicken myelin basic protein was determined and was found to be similar to that previously reported for mammalian myelin basic protein. The ratio N ^G, N '^G-dimethylarginine: N ^G-monomethylarginine:arginine was approximately 1.3:0.9:1.0. No N ^G, N ^G-dimethylarginine was detected in the protein. The in vivo incorporation of methyl groups from [methyl-³H]methionine into methylarginines in myelin was found to occur readily in 2-day-old chickens. Radioactively labelled N ^G, N '^G-dimeth-ylarginine and N ^G-monomethylarginine in myelin were derived solely from myelin basic protein. Radioactivity was also incorporated into N ^G, N ^G-dimeth-ylarginine, although this was not derived from myelin basic protein. As N ^G-monomethylarginine was easily separated from the dimethylarginines, and as it was derived from myelin basic protein, it may be a good marker for myelin basic protein turnover in vivo. A time course study of the incorporation showed that radioactivity was incorporated into N ^G-monomethylarginine up to 6 h after injection, and decayed slowly, with an apparent half-life of about 40 days.     

Stomata of trees growing in CO2-enriched air show reduced sensitivity to vapour pressure deficit and drought

Stomatal conductance ( g _s) and photosynthetic rate ( A ) were measured in young beech ( Fagus sylvatica ), chestnut ( Castanea sativa ) and oak ( Quercus robur ) growing in ambient or CO₂-enriched air. In oak, g _s was consistently reduced in elevated CO₂. However, in beech and chestnut, the stomata of trees growing in elevated CO₂ failed to close normally in response to increased leaf-to-air vapour pressure deficit (LAVPD). Consequently, while g _s was reduced in elevated CO₂ on days with low LAVPD, on warm sunny days (with correspondingly high LAVPD) g _s was unchanged or even slightly higher in elevated CO₂. Furthermore, during drought, g _s of beech and chestnut was unresponsive to [CO₂], over a wide range of ambient LAVPD, whereas in oak g _s was reduced by an average of 50% in elevated CO₂. Stimulation of A by elevated CO₂ in beech and chestnut was restricted to days with high irradiance, and was greatest in beech during drought. Hence, most of the additional carbon gain in elevated CO₂ was made at the expense of water economy, at precisely those times (drought, high evaporative demand) when water conservation was most important. Such effects could have serious consequences for drought tolerance, growth and, ultimately, survival as atmospheric [CO₂] increases.     

DOUBLE PULSE LABELLING WITH 3H-THYMIDINE: A METHOD FOR CALCULATING CELL POPULATIO KINETICS

A method was developed for calculating cell population kinetics with the aid of double pulse labelling with ³H-TdR. The labelling index was measured from auto-radiographs of the oral epithelium of two groups of 30-day-old rats. One group was injected once with ³H-TdR the other twice, with a time interval of 90 min between injections. DNA synthesis time was calculated from the equation:
   
where T _s= synthesis time; LI₁= labelling index in the single-injected group; LI₂= labelling index in the double-injected group; and T _i= time interval between injections. Synthesis time in the palate was 4.8 hr and 7.6 hr in the tongue. Generation time was calculated from the equation: T _g= ( T _s/LI₁) × 100, where T _g= generation time. Generation time in the palate was 46.1 hr and 75.8 hr in the tongue     

较长时间内15N标记的氨态氮和硝态氮在小嵩草草甸中的运移规律

运用15N稳定性同位素技术,对15N标记的硝酸盐和铵盐在输入小嵩草(Kobresia pygaea C.B.Clarke)草甸11～13个月后的运移规律进行了研究.在经历11～13个月后,进入无机氮库中的15N很少,一般不超过所输入氮素的l%,而较多的1 5N为土壤有机质、土壤微生物和植物所固持.NO3--15N和NH4 -1 5N在小嵩草草甸中的运移规律差异很大.在11、12和13个月后,NO3--15N的总恢复率分别为92.83%、92.64%和79.96%;而NH4 -15N的则分别为49.6%、63.33%和66.22%.两者的差异在土壤有机质、土壤微生物和植物等库之间的分配中更加明显.输入NO3--15N时在11、12个月后植物所固持的15N最多,而土壤微生物和土壤有机质所固持的15N比较接近,而在13个月后,土壤有机质和植物所固持的15N接近,而土壤微生物所固持的15N下降许多;当输入NH4 -15N,土壤有机质所固持的1 5N比植物和土壤微生物所固持的都多,而且植物所固持的15N比较稳定,而土壤微生物所固持的15N则有较大变化.这表明在较长的时间内嵩草草甸对NO3-和NH4 的固持能力是不一样的.     

Effect of H2O on energy-dependent oxidoreduction of cytochrome b

The rate of oxidation of the long-wavelength cytochrome b (b₅₆₆) on addition of oligomycin to ATP-supplemented anaerobic rat-liver mitochondria was strongly inhibited when ²H₂O was substituted for medium water. This effect was dependent on added substrate, was reversed by uncoupling agents, and was absent in sub-mitochondrial particles. At the same phosphate potential, b₅₆₆ reduction was favoured in ²H₂O in comparison with H₂O medium. The redox state of b₅₆₆ may be controlled by the phosphate potential via an intramembrane acid-base equilibrium which is shifted by ²H₂O.     

The influence of reduced photorespiration on long-term growth and development of wheat

The long-term role of photorespiration was investigated by comparing growth, development, gas exchange characteristics and mineral nutrition of a wheat crop ( Triticum aestivum L. cv. Courtot) cultivated in a culture chamber during a life cycle, either in 4% O₂ or in normal O₂ Low O₂ pressure reduced photorespiration, but CO₂ was controlled so that net photosynthesis remained the same as in the control crop. The growth and development of the low O₂ crop was slowed down. Ear appearance was 16 days late, but the rate of tillering was the same as in the control and was maintained longer so that the final number of tillers was doubled. Pigment, ribulose bisphosphate carboxylase (EC 4.1.1.39) and soluble sugar contents were similar. The response of photosynthesis to CO₂ and O₂ was not appreciably changed by the low O₂ treatment. There was almost no seed formation, and the senescence of the leaves was delayed. It appears that in non-stress conditions most of the photorespiration can be suppressed without damage to the photosynthetic apparatus. Retardation of development and inhibition of reproduction are likely due to other effects of O₂.     

Properties of ionophore-resistant Bacteroides rurninicola enriched by cultivation in the presence of tetronasin

Bacteroides ruminicola M384 was grown in the presence of increasing concentrations of tetronasin, an ionophore that has been developed as a feed additive for ruminants. The resulting culture, B. ruminicola M384/Tn^R, was then maintained in medium containing 0.1 pg tetronasin/ml. Growth of the parent strain was eliminated by the addition of 0.1 ug tetronasin/ml, but the growth rate of B. ruminicola M384/Tn^R, which grew more slowly than the parent strain, was unaffected by adding tetronasin. Bacteroides ruminicola M384/Tn^R retained its resistance to tetronasin even after repeated subculture in the absence of the ionophore, suggesting that a mutation had occurred. The absence of plasmids in individual colonies of B. ruminicola M384/Tn^R implied that the mutation was chromosomal. Bacteroides ruminicola M384/Tn^R was also more resistant to the ionophores monensin and lasalocid and, to a lesser degree, to the antibiotic avoparcin than B. ruminicola M384. Binding of [¹⁴C]tetronasin to B. ruminicola M384/Tn^R was lower than binding of the ionophore to the parent stain, and this difference was eliminated by washing cells with EDTA. The peptidolytic activity of B. ruminicola M384 towards triphenylalanine ( M _r= 460) was unaffected in B. ruminicola M384/Tn^R, but the rate of breakdown of tetra-phenylalanine ( M _r= 607) was decreased. This difference was also abolished by EDTA. It was concluded that growth of B. ruminicola in the presence of tetronasin resulted in a mutation affecting the permeability of the cell envelope, such that permeation of tetronasin and molecules of a similar size ( M _r= 628) was decreased.     

若尔盖高原沼泽湿地N2O排放通量研究

应用静态箱/气相色谱法,测定了若尔盖高原沼泽N₂O排放能量,测定期为该地植物生长期,即2004年4月末至10月初。结果表明,若尔盖高原沼泽湿地N₂O排放通量平均值为0.010mg·m^-2h^-1,最大值为0.079mg·m^-2h^-1,最小值为-0.051mg·m^-2h^-1。高峰排放期为5月,最低排放期为地表水深最大的6月。沼泽湿地N₂O排放通量季节变化与沼泽湿地水深呈负相关关系。沼泽湿地N₂O排放通量日变化与大气温度呈正相关关系,排放高值出现在午后。若尔盖高原沼泽湿地在植物生长期的年排放总量约为0.159Gg·a^-1。     

Activation of Sea Urchin Eggs by Halothane and Its Inhibition by Dantrolene

Eggs of the sea urchin, Hemicentrotus pulcherrimus , were stimulated by halothane, known to induce Ca²⁺ release from sarcosome, to cause fertilization membrane formation in normal and Ca²⁺ free artificial sea water. In the absence of external Ca²⁺, halothane-induced formation of fertilization membrane was inhibited by dantrolene, an inhibitor of Ca²⁺ release from sarcosome, but was not blocked by nifedipine, a Ca²⁺ antagonist specific to Ca²⁺ channels in plasma membrane. Ca²⁺ release from sedimentable fraction isolated from eggs was induced by halothane and was inhibited by dantrolene, but was not blocked by nifedipine. In normal artificial sea water, halothane-caused egg activation was not inhibited either by dantrolene or by nifedipine, but was blocked in the presence of both compounds. ⁴⁵Ca²⁺ influx was substantially stimulated by halothane in eggs exposed to ⁴⁵CaCl₂. Halothane-induced ⁴⁵Ca²⁺ influx into eggs was inhibited by nifedipine but was not blocked by dantrolene. When Ca²⁺ release from intracellular organellae is blocked, Ca²⁺ transport through Ca²⁺ channels in plasma membrane probably acts as a "fail-safe" system to induce an increase in cytosolic Ca²⁺ level, resulting in egg activation.     

Sodium ion transport in Neurospora crassa

Na⁺ influx and efflux in Neurospora crassa RL21a can be studied separately to calculate net Na⁺ movements. In the absence of external K⁺, Na⁺ influx was independent of the K⁺ content of the cells, but when K⁺ was present, the inhibition of Na⁺ influx by external K⁺ was higher the higher the K⁺ content. Efflux depended on the K⁺ and Na⁺ content, and on the history of the cells. Efflux was higher the higher the Na⁺ and K⁺ contents, and, in low-K⁺ cells, the efflux was also higher in cells grown in the presence of Na⁺ than when Na⁺ was given to cells grown in the absence of Na⁺. Addition of K⁺ to cells in steady state with external Na⁺ resulted in a net Na⁺-loss. In cells grown without Na⁺ this loss was a consequence of the inhibition of Na⁺ influx. In Na⁺-grown cells, addition of K⁺ inhibited Na⁺ influx and increased Na⁺ efflux.     

The effect of short-term H2S fumigation on water-soluble sulphydryl and glutathione levels in spinach

Abstract. Short-term fumigation of Spinacia oleracea with 380 μg m⁻³ H₂S (250 ppb) resulted in a rapid accumulation of water-soluble SH-compounds in the shoots. After 1 h exposure a substantial increase in the SH-content was already detectable and maximal accumulation, three- to four-fold that in control plants, was observed after 24 h of exposure. Irradiation during H₂S exposure only slightly affected the rate and level of SH-accumulation. H₂S fumigation did not affect the water-soluble SH-content of the roots. Glutathione was the sole water-soluble SH-compound accumulating upon exposure to H₂S. It was calculated that during the first hour of exposure to 380 μg m⁻³ H₂S 39% of the possible absorbed H₂S was converted into glutathione. The SH-content of the water-soluble proteins of the shoots was not affected by H₂S exposure. When fumigation was stopped, a rapid decrease in glutathione content was observed and after 48 h the content was comparable to that of the control plants. Contrary to H₂S, SO₂ fumigation did not result in a rapid accumulation of glutathione in spinach shoots. The possible role of glutathione accumulation during H₂S fumigation is discussed.     

Membrane inlet mass spectrometric analysis of N-isotope labelling for aquatic denitrification studies

Abstract: Techniques are described for measuring the isotope distribution in dissolved nitrate and N₂ using membrane inlet mass spectrometry, which allows several gases to be measured in a water sample without the need for any separation steps. The isotope distribution in dissolved nitrate was measured using denitrifying Pseudomonas nautica to reduce the nitrate to N₂ which was then measured by mass spectrometry. Pseudomonas nautica NCIMB 1967 was easily grown in nitrate-limited continuous culture minimising intra- or extracellular nitrate or nitrite pools, and the bioassay was tolerant of a range of salinities. The precision of the bioassay when measuring samples with high ¹⁵NO₃⁻ contents (0.5 μmol) was 0.05 atom%; with 0.1 μmol ¹⁵NO₃⁻, the precision was around 0.2 atom%. Differences in labelling of N₂ in preserved samples obtained from ¹⁵NO₃⁻ incubations of water-covered sediment cores were measured on parallel samples with membrane inlet MS and GC-MS. The membrane inlet technique was accurate but the precision on ratio measurements was lower than by GC-MS.     

CAPABILITY OF TUBULIN AND MICROTUBULES TO INCORPORATE AND TO RELEASE TYROSINE AND PHENYLALANINE AND THE EFFECT OF THE INCORPORATION OF THESE AMINO ACIDS ON TUBULIN ASSEMBLY

Abstract— Incorporation of [¹⁴C]tyrosine into the C-terminal position of α-tubulin of rat brain cytosol was 10-fold higher for non-assembled than for assembled tubulin. The incorporation into tubulin from disassembled microtubules was higher than into non-assembled tubulin; therefore, the low incorporation into microtubules was not due to a lower acceptor capacity of their tubulin constituent.
[¹⁴C]Tyrosine was released from assembled and non-assembled [¹⁴C]tyrosinated tubulin by the action of an endogenous carboxypeptidase. Release from non-assembled tubulin was shown by incubating a tubulinyl-[¹⁴C]tyrosine preparation in the presence of CaCl₂ at a concentration that abolished microtubule formation. Release from microtubules was inferred from the observation that the percentages of [¹⁴C]tyrosine released and the decrease of the specific radioactivity of the recovered microtubules were practically identical and did not change after a 10-fold dilution of the incubated microtubules.
[³H]Phenylalanine was released from a preparation of tubulinyl-[³H]phenylalanine also by an enzymatic activity.
The capacity of a tubulin preparation to incorporate tyrosine was increased 43% by pre-treatment with endogenous carboxypeptidase.
Tubulin tyrosinated in vitro was assembled to the same extent as native tubulin. After a mixture of tubulinyl-[¹⁴C]tyrosine and tubulinyl-[³H]phenylalanine was partially assembled, the ratio of ¹⁴C/³H found in the microtubules was the same as in the non-assembled tubulin fraction.     

Evaluation of Active Oxygen Effect on Photosynthesis of Chlorella vulgaris

The relationship between O₂ and an active oxygen scavenging system in Chlorella vulgaris var.vulgaris (IAM C-534) was investigated. When Chlorella vulgaris was exposed to 2% O₂, only traces of active oxygen scavenging enzymes were found. When the Chlorella vulgaris was treated with 20% or 50% O₂, it was shown that the level of enzyme activity increased as the O₂ concentration increased. An increase in enzyme activity was not found in any specific enzyme but in all of the enzymes, but the level of glutathione and ascorbate remained the same in all the cases. In addition, the photosynthetic efficiency also decreased as the concentration of O₂ was increased. These results suggest that an O₂ enriched environment can lead to an increase in the production of active oxygen species such as O_bullet2 and H₂O₂ and to a decrease in the photosynthetic efficiency in Chlorella vulgaris. The hydroxyl radical (^bulletOH) was detected directly in the Chlorella vulgaris suspension with a spin trapping reagent. It was also clear that the increase in the ^bulletOH intensity as the visible light intensity increased was unrelated to the O₂ concentration. It was suggested that the conditions for producing ^bulletOH and the other active oxygen species were different, and that two types of oxygen stress should exist in the Chlorella vulgaris.     

Effects of Extracellular Potassium on Acid Release and Motility Initiation in Toxoplasma gondii

The internal pH (pH_i) of Toxoplasma gondii was estimated by measuring the accumulation of the weak base 9-aminoacridine in buffers with various ionic compositions. The pH_i of the metabolizing parasite increased when the extracellular K⁺ was elevated in alkaline medium or when the external pH (pH_c) was substantially increased in medium employing high external K⁺ (90 mM). The parasite in mouse peritoneal fluid, or in potassium sulfate buffer (pH 8.2), where the pH_i was demonstrated to be increased to 7.9, became motile when acidic buffer was substituted for the original suspension medium. This acid-induced independent movement subsided within 5 min but was repeatedly induced if the pH_c was serially lowered to 6.0. Basic buffers, on the other hand, abolished motility when applied to the moving parasites. Nigericin, which is known to collapse pH gradients across the membrane, also abolished motility.     

Azimuthal variation in nighttime sap flow and its mainly influence factors of Populus tomentosa

为明确毛白杨(Populus tomentosa)不同方位夜间蒸腾量(Nt)及茎干充水量(Sr)等夜间液流活动的规律, 探究不同方位Nt和Sr的主要影响因子, 该研究使用热扩散的方法监测了宽窄行模式下栽植的毛白杨茎干不同方位夜间液流, 并用图像法区分Nt和Sr。使用自动气象站和机械式张力计监测太阳总辐射(R_s, kW·m^-2)、空气温度(T_a, ℃)、空气相对湿度(RH, %)、风速(v, m·s^-1)、土壤水势(ψ, kPa)等环境因子。通过比较各方位的Nt和Sr等液流活动的大小情况及其与环境因子之间的相关性得到方位间夜间液流的差异性以及各方位夜间液流的主要影响因子。结果显示: 宽行距位于东侧的样树西方位的Nt和Sr均最大, 其中西方位的Sr显著大于其他3个方位; 北方位的Nt显著小于其他3个方位; 其他方位间的Nt和Sr无显著差异; 各方位夜间茎干充水量占夜间液流量的比例(Sr/Q)无显著差异。宽行距位于西侧的样树西方位的Nt和Sr亦均最大, 其中西方位的Sr显著大于东方位和南方位; 南方位的Nt最小, 显著小于西方位和北方位, 其他方位间的Nt和Sr无显著差异; 南方位的Sr/Q显著大于其他3个方位。各方位的Nt和Sr均与水汽压亏缺(VPD)有显著的正相关关系, 部分方位Nt和Sr与T_a和RH有显著相关关系, 没有任何方位Nt和Sr与v和ψ有显著相关关系。Nt和Sr方位间的差异(Nt_CV、Sr_CV)与VPD、T_a、RH、v和ψ均无显著相关关系。此外, Sr受白天的液流活动的影响显著。综上所述, 毛白杨不同方位Nt和Sr等液流活动具有较大的差异, 且西方位是优势方位; VPD是影响各方位Nt和Sr的主要气象因子。     

毛乌素沙地油蒿-杨柴灌丛生态系统蒸散组分分配及其影响因子

蒸散发(ET)是生态系统水分循环和能量流动的重要组成部分,准确估算ET及其各组分,对认识生态生理过程对水分平衡和植物水分利用策略的影响具有重要意义。本研究于2019年5月20日至9月15日,利用涡度相关技术和微型蒸渗仪对毛乌素沙地油蒿-杨柴灌丛生态系统ET、蒸发(E)和蒸腾(T)进行测定和估算,量化了油蒿-杨柴灌丛生态系统ET组分,并分析ET及其组分的季节特征及影响因素。结果表明: T为毛乌素沙地油蒿-杨柴灌丛生态系统生长季ET的主要组分,T/ET为53.1%。T/ET值随降水减少而升高,E/ET值随降水减少而减少,蒸散组分分配主要受降水调控。在季节尺度上,E与10 cm深处土壤含水量(SWC₁₀)和太阳净辐射(R_n)呈显著正相关,其中,SWC₁₀是E的主要影响因素;T随R_n和叶面积指数(LAI)的升高而升高,随30 cm处土壤含水量(SWC₃₀)的升高呈先升高后降低的单峰趋势,受到SWC₃₀、R_n和LAI的共同影响;水分是ET的主要影响因素。生长季蒸散/降水量(ET/P)为109.2%,5月ET/P为250.5%,表明生长季初期ET耗水部分来自非生长季降水。     

Calcium ion transport across discs of the cortical flesh of apple fruit in relation to fruit development

Transport of Ca²⁺ through discs of apple fruit tissue was examined in tissue taken at different stages of fruit development. Transport rates decreased with fruit development when cation exchange was the predominant influence on transport (with 10⁻⁶ M ⁴⁵CaCl₂ as the source solution). This decrease was associated with a reduction in relative cell wall surface area, cation exchange capacity and cell wall yield that occurred during fruit growth. When diffusion was the major transport force, and when transport was influenced by solution infiltration of the tissue disc (10⁻² M ⁴⁵CaCl₂ in the source solution), transport rates increased during fruit growth. This increment was related to increases in air space of the tissue. Ca²⁺ transport through apple fruit tissue is influenced by the extent and nature of the cell wall, changing proportions of air space and Ca²⁺ concentration in the extracellular solution.     

DOES COLCHICINE AFFECT AGGREGATION OF NORMAL AND TRANSFORMED BHK CELLS DIFFERENTLY?

The effect of colchicine and vinblastine on cell aggregation was studied, using BHK cells and their transformed derivatives (pyBHK cells). When cells were dissociated with EDTA and the assay was made in a Ca²⁺-containing medium, the aggregation of transformed cells was prevented by colchicine and vinblastine, whereas the aggregation of normal cells was unaffected. When a Ca²⁺-free medium was used for aggregation, neither type of cell was influenced by these drugs. BHK and pyBHK cells, dissociated by trypsin in the presence of Ca²⁺, can aggregate only in the Ca²⁺-containing medium and the aggregation of both cell types was equally prevented by colchicine and vinblastine. Based on these results, it was concluded that colchicine and vinblastine inhibited the Ca²⁺-dependent mechanism of cell adhesion, but not the Ca²⁺-independent one which occurs in the Ca²⁺-free aggregation medium.     

THE EFFECT OF DENERVATION ON INCORPORATION OF 32P AND [3H]GLYCEROL BY THE MUSCLE MEMBRANE

Abstract— The incorporation in vivo of ³²P₁ was significantly increased in all glycerophosphatide of preparations of denervated muscle membrane in frogs. There was no increase in incorporation of ³²P₁ into sphingomyelin. Disuse induced by tenotomy did not significantly increase incorporation of ³²P₁ into phospholipids of the muscle membrane. The phospholipid content of muscle membranes remained unchanged as a result of denervation or tenotomy. Denervation produced an increase in the incorporation of [2-³H]glycerol into all glycerophosphatides in parallel with the increase in ³²P₁ incorporation. Although the stimulated incorporation of ³²P₁ was increased in the regions of the muscle membrane rich in endplates, the most marked effect was in the endplate-poor region where activity in phosphatidylserine was most markedly increased.