NaCl胁迫对玉米根质膜H^＋分泌和氧化还原系统的影响

玉米(Zea mays L.)根相对伸长速率(RER)、质膜H~ 分泌速率和Fe(CN)_6~(3-)还原速率均随NaCl浓度的增加而下降。随着胁迫时间的延长,H~ 分泌速率又有不同程度恢复,Fe(CN)_6~(3-)还原速率则随胁迫时间的延长而下降。NaCl胁迫时间在12h前,随着NaCl浓度的增加NADH的氧化速率也增加,超过12h明显下降。在同一NaCl浓度下,NADH氧化速率随胁迫时间的延长而下降。统计结果表明,盐胁迫下BER与H~ 分泌速率的相关系数为0.9998。所以,盐胁迫对根伸长生长的抑制可能与质膜H~ -ATPase和氧化还原系统等H~ 分泌过程的抑制有关。     

花生幼苗下胚轴质膜氧化还原系统

花生幼苗下胚轴细胞膜制剂具有氧化NAD(P)H,还原Fe(CN)_6~(3-)与EDTA-Fe~(3 )的能力,当Fe(CN)_6~(3-)浓度为1mmol/L时,膜制剂氧化NADH和NAD(P)H的K_m分别为100和110μmol/L;V_(max)为1400和710nmol mg~(-1) proteinmin~(-1),最适pH为8.0。NADH 0.25 mmol/L浓度下,膜制剂还原Fe(CN)_6~(3-)的K_m为40,V_(max)为1300;还原EDTA-Fe~(3 )的K_m为125,V_(max)为180,最适pH分别为8.0与7.0。氧为该系统天然受体,鱼藤酮、抗霉素A与CN~-对其活性无影响,10μmol/L的DCCD抑制其活性约20％,10μmol/L的SHAM抑制近50％活性。     

渗透调节对低温伤害敏感大豆种子质膜氧化还原活性的影响

选用对吸胀冷害敏感的大豆[Glycine max(L.)Merr.]品种"黑河23"种子为试材,研究了渗透调节增强大豆种子活力过程中种子质膜氧化还原活性的变化.结果表明,大豆种子活力指数与种子质膜氧化还原活性呈正相关.与对照相比,渗控12 h显著提高大豆种子活力,表现在发芽指数、活力指数和TF生成量的提高,种子质膜NADH和NADPH氧化速率及Fe(CN)63-和EDTA-Fe3 还原速率明显上升;随着引发时间的延长,种子活力上升变缓,种子质膜NADH和NADPH氧化速率及Fe(CN)63-还原速率上升速度变慢,EDTA-Fe3 的还原速率在渗控24 h后开始下降,但渗控72 h仍高于对照.     

小麦根质膜氧化还原系统及其对水分胁迫的反应（简报）

小麦根质膜制剂氧化NADH的Km为60μmol／L,Vmax为1127nmol／mg蛋白mini还原K3Fe（CN）6的Km为272μmol／L,Vmax为3205nmol／mg蛋白min。两者的最适pH为7．5,最适温度是40℃。KCN、SHAM、Na3VO4对质膜氧化还原活性无影响,DCCD则有抑制作用（10％）。水分胁迫下活体质膜与离体质膜的K3Fe（CN）6还原活性变化呈相反变化趋势。     

Cd2+ 、Zn2+单一及复合胁迫对凤眼莲根质膜3种氧化还原酶活性的影响

采用水培法研究了不同浓度Cd2+ 、Zn2+单一及复合胁迫(0.05和0.50 mmol·L-1 Cd2+,0.5和5.0 mmol·L-1 Zn2+)对凤眼莲[Eichhornia crassipes (Mart. ) Solms]幼苗根质膜3种氧化还原酶[NADH氧化酶、Fe(CN)63-还原酶和EDTA-Fe3+还原酶]活性的影响. 结果表明, Cd2+ 、 Zn2+单一及复合胁迫对凤眼莲根质膜NADH氧化酶、Fe(CN)63-还原酶及EDTA-Fe3+还原酶活性的影响效应有明显的差异.0.05或0.50 mmol·L-1 Cd2+单一胁迫处理20 h可使凤眼莲根质膜3种氧化还原酶活性均较对照显著降低(P≤0.05),0.5或5.0 mmol·L-1 Zn2+单一胁迫20 h可导致凤眼莲根质膜NADH氧化酶和EDTA-Fe3+还原酶活性也均较对照显著降低(P≤0.05).随胁迫时间的延长,Cd2+ 、 Zn2+单一及复合胁迫处理均可使凤眼莲根质膜氧化还原酶活性增强,胁迫处理20 d时凤眼莲根质膜3种氧化还原酶活性均高于胁迫20 h的活性.Cd2+-Zn2+复合胁迫对凤眼莲根质膜3种氧化还原酶活性的影响效应因作用时间和胁迫浓度的不同而有一定的差异;在胁迫20 h时,Cd2+与Zn2+之间对凤眼莲根质膜3种氧化还原酶活性的作用关系较复杂,因胁迫浓度的不同表现出协同或拮抗的关系;胁迫20 d时,Cd2+与Zn2+对凤眼莲根质膜3种氧化还原酶活性的复合影响表现出明显的拮抗关系.研究结果显示,Cd2+ 、 Zn2+对凤眼莲根质膜氧化还原酶的复合作用效应与Cd2+和Zn2+的浓度比例及胁迫时间均相关.     

在耐热性诱导中豌豆叶片过氧化氢和水杨酸含量与质膜ATP酶活性的变化及相互关系

在高温锻炼(37℃,2h)过程中,豌豆(Pisum sativum L.)叶片过氧化氢(H_2O_2)和游离态水杨酸(SA)含量与质膜ATP酶(H~ -ATPase)活性都有一个高峰,H_2O_2的迸发早于游离态SA的积累,而质膜H~ -ATPase活性高峰的出现则迟于SA高峰;活性氧清除剂、抗氧化剂、质膜NADPH氧化酶抑制剂和H_2O_2的淬灭剂预处理均可有效地阻止高温下H_2O_2和SA的积累以及质膜H~ -ATPase活性的增加。根据以上结果推测,H_2O_2、质膜H~ -ATPase和SA均参与耐热性诱导相关的信号传递,前者作用于SA的上游,而后者在SA下游起作用。     

钒酸钠、叠氮钠对小麦根细胞K~+吸收和质膜K~+-Mg~(2+)-ATPase的作用

Neurospora细胞膜质子泵(H~+-ATPase)专一性抑制剂钒酸钠,抑制小麦离体根K~+的吸收与H~+分泌,并抑制小麦根细胞膜-K~+-Mg~(2+)-ATPase活力。它对K~+吸收的抑制效应,可能是抑制质膜K~+-Mg~(2+)-ATPase活力的结果。而且在起抑制作用的时间上有明显地不同,表明钒酸钠对K~+、H~+在细胞膜中的通道影响不同。叠氮钠解链小麦根的呼吸,降低根细胞的ATP水平,但从实验开始就完全抑制小麦根K~+的吸收,对质膜K~+-Mg~(2+)-ATP-ase的活力没有影响。可能叠氮钠只阻止“载体”对K~+接受的过程。应用~86R_b+示踪的K~+吸收试验表明,钒酸钠对小麦根K~+吸收的抑制%,不为增加外部溶液K~+浓度而减低。增加底物ATP浓度,也不能减低钒酸钠对质膜-ATPase的抑制%。钒酸钠的抑制作用是非竞争性抑制。~3H-亮氨酸渗入试验表明钒酸钠对“载体”的合成没有干扰作用。VO_4~(3-)离子明显促进小麦根的呼吸,并提高根细胞的ATP水平,这种ATP水平的提高,可能是质膜-ATPase受到抑制,主动运输过程减弱的结果。     

植物细胞质膜氧化还原系统

从研究材料、实验方法、氧化还原活性、氧化还原组分以及生理功能等方面介绍70年代末发现的植物细胞质膜氧化还原系统的研究进展。此系统与铁和溶质的吸收、细胞的生长、细胞对蓝光的反应等生理过程有密切的关系,它是质膜H~+-ATPase外的另一能量转换系统。     

Effect of osmotic shock on the redox system in plasma membrane of Dunaliella salina

The unicellular halotolerant alga Dunaliella salina had the ability to oxidize NADH and reduce Fe(CN)6^3-.The redox reactions were to some extent stimulated by slight hyperosmotic shock (2.0mol/L→2.6mol/L NaCl),but markably inhibited by abrupt hyperosmotic shock (2.0mol/L→3.5mol/L NaCl) and hypoosmotic shock (2.0mol/L→1.0mol/L NaCl;2.0mol/L→0.67mol/L NaCl).With the adaptation of algal cells to osmotic shock by accumulating or degraging intracellular grycerol,the plasmalemma redox activities were also restored.The O2 uptake stimulated by NADH could be promoted by FA and SHAM.Hypoosmotic shock increases the basal respiration rate of alga cells,but weakened the stimulating effects of NADH,FA and SHAM on O2 uptake.On the other hand,hyperosmotic shock reduced the basal respiration rate,but relatively enhanced the above effects of NADH,FA and SHAM.H^ extrusion of alga cells was inhibited by NADH and stimulated by Fe(CN)6^3-.Vanadate and DES could inhibit H^ efflux,but had little effect in the presence of NADH and Fe(CN)6^3-.Both hyperand hypoosmotic shock stimulated H^ extrusion.This effect could be totally inhibited by vanadate and DES,but almost unaffected by 8-hydroxyquinoline.It was suggested that H^ -ATPase probably played a more important role in H^ extrusion and osmoregulation under the conditions of osmotic shock.     

牛脾胆绿素还原酶的性质

纯牛脾胆绿素还原酶是单一蛋白质,分子量约34 000,等电点约6.2。该酶对胆绿素具有专一性,在还原胆绿素为胆红素中,以还原胆绿素Ⅸ_α最快,Ⅸ_β、Ⅸ_γ和Ⅸ_δ皆很慢。于还原反应中,此酸可以NADH为电子和氢供体,NADPH亦然。然而,NADH依赖性酸与NADPH依赖性酶动力学性质不同:与NADH反应的最适pH7.0,而与HADPH反应时为8.5;两者活性均为过量的胆绿素所抑制,不过,NADPH依赖性酶更敏感。     

Ectogenesis and the case against the right to the death of the foetus

Ectogenesis, or the use of an artificial womb to allow a foetus to develop, will likely become a reality within a few decades, and could significantly affect the abortion debate. We first examine the implications for Judith Jarvis Thomson’s violinist analogy, which argues for a woman’s right to withdraw life support from the foetus and so terminate her pregnancy, even if the foetus is granted full moral status. We show that on Thomson’s reasoning, there is no right to the death of the foetus, and abortion is not permissible if ectogenesis is available, provided it is safe and inexpensive. This raises the question of whether there are persuasive reasons for the right to the death of the foetus that could be exercised in the context of ectogenesis. Eric Mathison and Jeremy Davis have examined several arguments for this right, doubting that it exists, while Joona Räsänen has recently criticized their reasoning. We respond to Räsänen’s analysis, concluding that his arguments are unsuccessful, and that there is no right to the death of the foetus in these circumstances.     

On the diversity of the Cladocera in the tropics

The mythical concept of an impoverished tropical cladoceran fauna is refuted. On a planetary scale, around half of the cladoceran species presently known occur exclusively in the tropics-subtropics, often with considerable restriction to particular geographical subzones. On a regional (political) scale, the situation is often unclear because of the continued fragmentary nature of studies, and because political units are not a good basis for biogeographical comparisons. At the finest level of resolution (lake-perlake comparisons), there appears to be an upper limit of c. 50 cladoceran species per individual lake. No significant difference between lakes in the temperate zone and in the tropics could be established here. Daphnia is largely absent from the tropics, but is replaced by more Sidids, Moinids, and Bosminids, such that the average cladoceran community in the limnetic zone of a tropical lake is not characterized by less species but rather by lower population densities. This, in turn, is considered a consequence of higher prevalent predation levels in the tropics.     

Tubular networks in the terminal endings of the visual receptor cells in the human,the monkey,the cat and the dog

Summary A tubular network was found in the terminal endings of the visual receptor cells in the human, the monkey (Macaca mulatta), the cat and the dog. These tubules are arranged in close groups in the vicinity of the synaptic lamellae and the invaginated dendrites. According to the form, diameter, density of the tubules and to the consistence of the network formed by them one can distinguish at these places an initial type (type I), a transitory (type II) and a vesicular one (type III). In the the type III branching, bizarre forms are frequent. The diameter of all the tubules reaches 500–600 Å, their density and walls being the same as in the synaptic vesicles.Similar networks also occur in the axons of the visual receptor cells of the monkey.

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Zusammenfassung In den Endigungen der Photorezeptorzellen von Mensch, Affe (Macaca mulatta), Katze und Hund kommen aus Tubuli bestehende Komplexe vor. Organellenartig in geschlossenen Gruppen angeordnet, liegen sie in Nähe der synaptischen Lamellen und der invaginierten Dendriten. An diesen Stellen kann man nach Form, Durchmesser, Dichte und Konsistenz der von den Tubuli gebildeten Komplexe drei Typen unterscheiden: 1. einen initialen (Typus I), 2. einen Übergangstypus (Typus II) und 3. einen vesiculären Typus (Typus III). In letzterem kommen häufig verzweigte, bizarre Formen vor. Der Durchmesser sämtlicher Tubuli erreicht 500–600 Å. Ihre Dichte und ihre Wand gleicht denen der synaptischen Vesikel.Ähnliche Komplexe fanden wir auch in den Axonen der Photorezeptorzellen vom Affen.

     

Assessing the Physiological State of the Fucoids from the Barents Sea Littoral by the End of the Polar Night

Methods of amperometry and potentiometric titration were used to follow dark respiration (DR) and apparent photosynthesis (AP) in the fucoids Ascophyllum nodosum (L.) Le Jol, Fucus vesiculosus L., and F. serratus L. from the Barents Sea littoral by the end of the 40-day-long polar night. The macroalgae were shown to manifest species-specific low rates of photosynthesis and respiration. However, in spite of their low photosynthetic status due to the effects of subzero temperature and prolonged low or zero illumination, the macroalgae have been able to restore DR and AP to the initial level already by the day 9; the ability to restore AP depended on the level of illumination. The study of the changes in the carbonate–bicarbonate system in the light and darkness demonstrated that the macroalgae grown in darkness, in contrast to those grown in twilight, could absorb bicarbonate in darkness; however, they lost this capacity after two-day-long illumination at an irradiance of 7 mol/(m² s). Bicarbonate uptake in darkness and the capacity to restore the systems of photosynthesis and respiration in fucoid cells are discussed in the context of algal energy metabolism under the polar night conditions.     

Arranging the elements of the potassium channel: the T1 domain occludes the cytoplasmic face of the channel

The voltage-gated potassium channel is currently one of the few membrane proteins where functional roles have been mapped onto specific segments of sequence. Although high-resolution structures of the transmembrane portions of three bacterial potassium channels, the tetramerization domain and the cytoplasmic ball are available, their relative spatial arrangement in mammalian channels remains a matter of ongoing debate. Cryo-electron microscopic images of the six transmembrane voltage-gated Kv channel have been reconstructed at up to 18 Å resolution, revealing that the T1 domain tetramerizes and is suspended below the transmembrane segments. However, the resolution of these images is insufficient to reveal the location of the third piece of the puzzle, the inactivating ball domain. We have used the aberrant interactions observed in a series of chimæric channels to establish that an assembled T1 domain restricts access to the cytoplasmic face of the channel, suggesting that the N-terminal ball and chain may be confined in the space between the T1 domain and the transmembrane portion of the channel.     

Feeding the vertebrate retina from the Cambrian to the Tertiary

The retina of the vertebrate eye is metabolically active and requires nutritive support. During the last 540 million years it has evolved into forms as complicated and nutritionally demanding as those found in avian or primate eyes. Diffusion from the choroid is generally able to supply the metabolic needs of thin retinae. However, when the thickness exceeds the limits of diffusion, structures are needed to supplement the vascular supply from the choroid. These supplemental nutritive devices include the choroidal gland, the falciform process and preretinal vascular plexus of fish, the conus papillaris of lizards, the pecten oculi of birds, the intraretinal vessels of mammals and a few novel systems that remain difficult to classify. These vascular systems are among the most variable features of the vertebrate eye. Here, we review classical and recent findings regarding such retinal nutrition systems, propose a three category classification for them based on histologic origins and speculate on the evolutionary forces which drove their development.     

Observations on the permeability of the choriocapillaris of the eye

Summary The choriocapillaris is a fenestrated capillary bed located posterior to the retinal pigment epithelium. It serves as the main source of supply to the photoreceptors, retinal pigment epithelium, and other cells of the outer retina. The permeability of these capillaries to intravenously injected ferritin (MW — approx. 480,000; mol. diam. 11 nm) was examined in the mouse, rabbit, and guinea pig, each of which is characterized by a different type of retinal vascularization. In all three species, the bulk of the ferritin remained in the capillary lumina, where it appeared to be blocked at the level of the diaphragmed fenestrae. Some ferritin was present in endothelial cell vacuoles. The results confirm previous work on the rat choriocapillaris and indicate that the barrier function of the choriocapillary endothelium is present even among species in which the retinal circulation differs significantly.Supported by NIH grant EY03418