Phylogenetic place of guinea pigs: no support of the rodent-polyphyly hypothesis from maximum-likelihood analyses of multiple protein sequences

Graur et al.'s (1991) hypothesis that the guinea pig-like rodents have an evolutionary origin within mammals that is separate from that of other rodents (the rodent-polyphyly hypothesis) was reexamined by the maximum-likelihood method for protein phylogeny, as well as by the maximum-parsimony and neighbor-joining methods. The overall evidence does not support Graur et al.'s hypothesis, which radically contradicts the traditional view of rodent monophyly. This work demonstrates that we must be careful in choosing a proper method for phylogenetic inference and that an argument based on a small data set (with respect to the length of the sequence and especially the number of species) may be unstable.      

葡萄试管苗热处理结合茎尖培养脱病毒效果的研究

对７个生食葡萄品种的试管苗热处理结合茎尖剥离培养脱除病毒的方法做了研究,结果表明,从热处理试管苗剥离的茎尖培养成活率为６１．２％,其中有１８．１％的成苗。各品种热处理试管苗剥离的茎尖分化再生能力不同：先形成愈伤组织的成苗率较低,而先分化芽的茎尖成苗率较高。这一方法对扇叶病毒和卷叶病毒的脱除率达９２％以上。     

Inhibition of mugineic acid-ferric complex uptake in barley by copper, zinc and cobalt

The interfering effects of copper, zinc, and cobalt on the uptake of mugineic acid-ferric complex were studied in barley ( Hordeum vulgare , cv. Minorimugi) grown in nutrient solution. Short-term uptake experiments of 3 h were performed utilizing both ionic and mugineic acid-complex forms of each metal at two different concentrations. Copper was most effective in decreasing iron uptake when added in an ionic form at either concentration. The inhibition order at higher concentrations followed Cu(II) > Zn(II) ≥ Co(II), Co(III), which is consistent with the stability constants of these metal complexes with mugineic acid. The displacement of iron from its mugineic acid complex by these metals is suggested as a probable explanation for the decreased iron uptake. The inhibitory effect of metal complexes with mugineic acid on iron uptake was only found in cases with higher concentrations of Cu(II) and Zn(II) complexes. Deformation of the specific iron transport system in the plasma membrane due to their adsorption may be responsible for this effect.     

Metabolite effectors for short-term nitrogen-dependent enhancement of phosphoenolpyruvate carboxylase activity and decrease of net sucrose synthesis in wheat leaves

It has been demonstrated previously that field pea (Pisum sativum L. cv. Express) grown in hydroponic culture on a complete nutrient solution with low NH₄⁺ concentrations (<0.5 mM) will produce a larger than normal proliferation of nodules. Peas grown in the absence of mineral N in hydroponic culture have been shown to rapidly autoregulate nodulation, forming a static nodule number by 14 to 21 days after planting. The present study further characterizes the effect of NH₄⁺ concentration in hydroponic culture on nodulation and nodule growth. Peas were grown continually for 4 weeks at NH₄⁺ concentrations that were autoregulatory (0.0 mM), stimulatory (0.2 mM) or inhibitory (1.0 mM), or peas were transferred between autoregulatory or NH₄⁺ inhibited and stimulatory solutions after 2 weeks. The peas nodulated as expected when grown under constant autoregulatory, stimulatory or inhibitory concentrations of NH₄⁺. When peas were transferred from the inhibitory (1.0 mM) to the stimulatory solution (0.2 mM) a massive proliferation of nodule primordia over the entire root system was observed within 3 days of the transfer. When they were transferred from the autoregulatory (0.0 mM) to the stimulatory (0.2 mM) solution a 10-day delay occurred before a proliferation in nodule primordia occurred at distal regions of the root system. These findings support our hypothesis that low concentrations (<1.0 mM) of NH₄⁺ in hydroponic culture cause a suppression of autoregulation in pea. In addition, the temporal and spatial differences in nodule proliferation between transfer treatments demonstrate at a whole plant level that autoregulation and NH₄⁺ inhibition suppress early nodule development via different mechanisms.     

Kinase requirement for retinal growth cone motility

Since cytoplasmic Ca²⁺ levels are reported to regulate neurite elongation, we tested whether calcium-activated kinases might be necessary for growth cone motility and neurite elongation in explant cultures of goldfish retina. Kinase inhibitors and activators were locally applied by micropipette to retinal growth cones and the responses were observed via phase-contrast videomicroscopy. In some cases, growth rates were also quantifed over several hours after general application in the medium. The selective inhibitors of protein kinase C, calphostin C (0.1–1 μM) and chelerythrin (up to 50 μM), caused no obvious changes in growth cones or neurite elongation, and activators of PKC (phorbols, arachidonic acid, and diacylglycerol) also were generally without effects, although phorbols slowed the growth rate. Inhibitors of protein kinase A and tyrosine kinases also produced no obvious effects. The calmodulin antagonists, calmidazolium (0.1 μM), trifluoperazine (100 μM), and CGS9343B (50 μM), however, caused a reversible growth cone arrest with loss of filopodia and lamellipodia. The growth cone became a club-shaped swelling which sometimes moved a short distance back the shaft, leaving evacuated filaments at points of strong filopodial attachments. A similar reversible growth cone arrest occurred with the general kinase inhibitors: H7 at 200 but not at 100 μM, and staurosporine at 100 but not 10 nM, suggesting possible involvement of a calmodulin-dependent kinase (camK) rather than PKC. The selective inhibitor of camKII, KN-62 (tested up to 50 μM), produced no effects but the specific myosin light-chain kinase (MLCK) inhibitors ML-7 (3–5 μM) and ML-9 (5–10 μM) reversibly reproduced the effect, suggesting that MLCK rather than camKII is necessary for growth cone motility. The MLCK inhibitors' effects both on growth cone morphology and on F-actin filaments (rhodamine-phalloidin staining) were similar to those caused by cytochalasin D (5 μM), and are discussed in light of findings that inhibiting MLCK disrupts actin filaments in astrocytes and fibroblasts. 1994 John Wiley & Sons, Inc.     

RGDS肽对大鼠主动脉球囊内膜剥脱后血管壁增殖的影响

在大鼠主动脉球囊内膜剥脱术后血管壁细胞过度增殖模型上,用合成的血小板膜纤维蛋白原受体（ｇｌｙｃｏｐｒｏｔｅｉｎⅡｂ／Ⅲａｃｏｍｐｌｅｘ,ＧＰⅡｂ／Ⅲａ）拮抗剂ＲＧＤＳ（Ａｒｇ－Ｇｌｙ－Ａｓｐ－Ｓｅｒ,５０μｍｏｌ·ｋｇ－１·ｄ－１）治疗可有效地抑制损伤血管壁的细胞计数增加和内膜增厚以及血管平滑肌细胞增殖,显著降低其血管组织３Ｈ－ＴｄＲ和３Ｈ－Ｌｅｕ的参入增加程度。实验结果提示ＲＧＤＳ肽作为血管成型术的辅佐剂,对于防治血管再狭窄可能具有潜在的临床应用前景。     

岩豆凝集素的圆二色性与生物学活性关系的研究

岩豆凝集素（ＭＤＬ）的远紫外圆二色性谱（ＣＤ谱）显示２１６－２１７ｎｍ处的单一负峰。此时ＭＤＬ分子含有１６．２％的α螺旋,４６．３％的β折叠和３７．５％的无规卷曲。ｐＨ９．０时负峰红移至２２０ｎｍ,且在２１７－２２２ｎｍ处的峰值几乎相同;在２０－４０℃范围内,ＣＤ谱的变化甚微;６０℃时谱峰蓝移;在８０℃或１００℃时,２１２ｎｍ处出现一大负峰。１ｍｏｌ／Ｌ或２ｍｏｌ／Ｌ脲时,ＭＤＬ的ＣＤ谱已发生明显变化,二级结构单元也有变化,凝集兔红细胞的活性也随之减弱;随脲浓度的增加,ＭＤＬ的谱峰蓝移,最终在２１２ｎｍ处出现大负峰。当胍浓度为０．７５ｍｏｌ／Ｌ时,ＭＤＬ的ＣＤ谱即有明显变化和活性丧失;胍浓度继续增加,ＣＤ谱逐渐成为特征的无规卷曲的谱形。在ｐＨ９．０、温度超过８０℃、脲或胍浓度分别高于２ｍｏｌ／Ｌ和０．７５ｍｏｌ／Ｌ时,ＭＤＬ的ＣＤ谱发生显著变化的同时,其凝集兔红细胞的生物学活性全部丧失,分子的二级结构单元也发生很大改变。     

广西HBsAg阳性母亲的胎儿肝、肾细胞中乙肝病毒DNA存在状态的研究

采用核酸分子杂交Ｓｏｕｔｈｅｒｎ印迹法,以３２Ｐ标记的ＨＢＶＤＮＡ为探针,检测ＨＢｓＡｇ阳性母亲引产的４０例胎儿的肝、肾组织。结果有２例胎肝和１例胎肾细胞ＤＮＡ出现大于３．２ｋｂ的杂交带,表明ＨＢＶＤＮＡ已处于整合状态。胎肾细胞基因组中查出ＨＢＶＤＮＡ整合为首次报道。     

Isolation of two novel corrinoid proteins from acetate-grown Methanosarcina barkeri.

Two corrinoid proteins with molecular sizes of 480 and 29 kDa are stably methylated by [2-14C]acetate-derived intermediates in cell extracts of aceticlastic Methanosarcina barkeri when methylreductase is inhibited by the addition of bromoethanesulfonic acid. Both 14CH3-proteins have been isolated to near homogeneity and found to be abundant soluble proteins. The larger protein possesses two subunits, of 41.4 and 30.4 kDa, in an equimolar ratio, suggesting an alpha 6 beta 6 conformation with six bound methylated corrinoids per 480-kDa molecule. The 29-kDa protein is a monomer in solution and possesses only one methylated corrinoid. All methyl groups on both proteins are photolabile, but the methylated corrinoid bound to the 29-kDa protein undergoes photolysis at a higher rate than that bound to the 480-kDa protein. The two proteins possess discrete N termini and do not appear to be forms of the same protein in equilibrium. Neither protein has an Fe4S4 cluster, and both have UV-visible spectra most similar to that of a base-on methylated corrinoid. A previously identified methylated protein, designated the unknown A 14CH3-protein, copurifies with the 480-kDa protein and has the same subunit composition. The methyl groups of both isolated 14CH3-proteins are converted to methane in cell extracts. The methylated proteins that accumulate in extracts in the presence of bromoethanesulfonic acid are demethylated by the addition of coenzyme M. Both isolated proteins are abundant novel corrinoid proteins that can methylate and be methylated by intermediates of the methanogenic pathway.     

A new computational method for cable theory problems.

We discuss a new computational procedure for solving the linear cable equation on a tree of arbitrary geometry. The method is based on a simple set of diagrammatic rules implemented using an efficient computer algorithm. Unlike most other methods, this technique is particularly useful for determining the short-time behavior of the membrane potential. Examples are presented and the convergence and accuracy of the method are discussed.