Oxygen-dependent electron transport and protection from photoinhibition in leaves of tropical tree species

The roles of photorespiration and the Mehlerperoxidase pathway in sustaining electron transport and protection from photoinhibition were studied in outer canopy leaves of two species of tropical trees: the drought-deciduous Pseudobombax septenatum (Jacq.) Dug. and the evergreen Ficus insipida Willd. Ficus had a higher photosynthetic capacity than Pseudobombax and also a greater capacity for light-dependent electron transport under photorespiratory conditions (in the absence of CO₂). As a consequence, in the absence of CO₂, Ficus was able to maintain a largely oxidized electron-transport chain at higher photon flux densities than Pseudobombax. Under the same light conditions, photoinhibition (reduction in F_v/F_m) was always greater in Pseudobombax than Ficus, was increased when leaves were exposed to 2% O₂ in nitrogen compared to 21% O₂ in CO₂-free air, but was not increased by the absence of CO₂. Rates of electron transport due to the Mehler-peroxidase pathway (assessed in 2% O₂ in nitrogen) ranged between 16–40 mol · m^–2·s^–1 in both species. As the dry season approached and Pseudobombax neared leaf senescence there was a decline in the capacity for photorespiratory flux to maintain electron transport in Pseudobombax, but not in Ficus. Ratios of light-dependent electron transport to net CO₂ fixation for Pseudobombax, Ficus and two other species in the field, Luehea seemannii Tr. & Planch, and Didymopanax morototoni (Aubl.) Dec. & Planch., ranged from 6.2 (Ficus) to 16.7 (Pseudobombax). High in-situ rates of photorespiration combined with the decreased capacity of Pseudobombax for photorespiratory flux as the dry season approached indicates a decreased capacity to protect against photooxidative damage. This may contribute to the promotion of leaf senescence in Pseudobombax during the transition from wet to dry season.Abbreviations F_v/F_m ratio of variable to maximum chlorophyll a fluorescence - NPQ nonphotochemical fluorescence quenching - PFD photon flux density - Q_A primary electron acceptor of PSII This research was supported by a grant from the Mellon Foundation. We thank Monica Mejia and Juan Posada for assisting with the fluorescence measurements and Aurelio Virgo for assisting with the field CO₂-exchange measurements.     

过氧化心肌线粒体产生的脂类自由基及（－）－EGCG的抑制作用

本文利用ＥＳＲ技术研究了心肌线粒体酶修饰下的脂质过氧化和脂类自由基,以及（－）－ＥＧＣＧ的抑制作用。结果表明：４－ＰＯＢＮ能捕集ｌｉｐｏｘｙｇｅｎｇｓｅ诱发心肌线粒体产生的自由基,得到６条线谱的脂类自由基和４条线谱捕集物,（－）－ＥＧＣＧ对该体系中使用的１ｉｐｏｘｙｅｎａｓｅ活性无影响,对所产生的自由基有明显的清除作用,并呈量效关系。对脂质过氧化的抑制作用,在本试验浓度范围内随浓度增加变化不大,最大抑制率约２０％。     

爪蟾脊索在决定过程中和相邻细胞的关系

已经知道,对预定脊索的决定起重要作用的是位于它两侧的预定肌节。电子显微镜的观察指出,预定脊索和肌节细胞相互靠得很近,或者相隔一定距离,以突起相连形成腔隙。有被小窝和小泡在两类细胞的外缘常被观察到。最引人注意的是在肌节细胞近腔隙的部位或者附近,球状体的出现。它们大小不等,内含物主要是颗粒,有的松散分布,有的致密地充满整个球状体。这些颗粒的大小和电子染色与这时期胚胎细胞中的核糖体很相似。在预定脊索细胞中以及附近,未见上述结构,但是,观察到它们伸出突起包吞腔隙中物质的现象。讨论了这些球状体的出现与脊索决定之间可能存在的关系。     

狂犬病毒“北京株”在地鼠肾传代细胞中增殖的电镜观察

用透射电子显微镜观察术,对狂犬病固定毒“北京株”在地鼠肾传代细胞（ＢＨＫ２１）中增殖的形态学变化进行了研究。在受感染的细胞中有大量子弹状和长杆状的病毒颗粒。大多数病毒在扩张的内质网膜上以出芽的方式发生,凸向内质网腔内并逐渐发育成子弹状和杆关的成熟病毒。含病的内质,多周围常伴有颗粒或丝状均质区域,少数病毒在细胞膜上芽生。细胞间隙中亦可见病毒。还见病毒在细胞核膜内、外层上芽生,核周围间隙中许多病毒,有     

Ultrastructure of the spermatozoa and eggs of the ocean pout (Macrozoarces americanus L.), an internally fertilizing marine fish

Ultrastructure of sperm and eggs of the ocean pout (Macrozoarces americanus L.), an internally fertilizing marine teleost, was examined by scanning and transmission electron microscopy. The results showed that the sperm do not have an acrosome but have a very long mid-piece (one to two times the sperm head length) containing numerous well-developed elongated mitochondria. The sperm also have two tails (is biflagellate) each consisting of nine peripheral and one central pair (9 ± 2) of microtubules. This long mid-piece and the biflagellate nature of the sperm appear to be associated with the long life-span of the sperm and with sperm dispersal in the ovary to fertilize the eggs internally. The ocean pout eggs are enveloped by a porous chorionic membrane similar to that found in other teleosts but have two micropyles, a condition likely related to a mechanism of egg fertilization which increases the egg fertlity in the presence of low sperm numbers. Following insemination, some biochemically undefined excretions appeared on the surface of fertilized eggs and led to the acquisition of adherent capability of the eggs which formed a tightly associated egg mass in sea water. © 1995 wiley-Liss, Inc.     

Mutual Contact of Adherent Polymorphonuclear Leukocytes Inhibits Their Generation of Superoxide

Superoxide generation by polymorphonuclear leukocytes (PMNs) in suspension, or adherent to glass or plastic, after stimulation with /V-formylmethionyl-leucyl-phenylalanine or phorbol myristate acetate was measured by cytochromec reduction and spin trapping. Amounts of superoxide generated by adherent PM Ns were inversely related to cell density. The generation of hydrogen peroxide was also inhibited at higher cell densities. In contrast to adherent cells, superoxide released by PMNs in suspension linearly increased with respect to cell number over a wider range. Microscopic observation indicated that the number of cells in mutual contact increased rapidly at cell densities higher than 4 × 10⁴ cells/cm², and inhibition of superoxide became apparent at higher cell densities. Mediators which could be released by PMNs, such as NO and adenosine, were not the cause of inhibition. Thesedatu suggest that mutual contact of PMNs suppresses their generation of superoxide. Survival rates of PMNs after stimulation increased at higher densities, indicating that the mutual contact-induced inhibition of superoxide generation by PMNs may be physiologically relevant at sites of inflammation.     

Fine structure and lectin histochemistry of the apical surface of the free neuromast of Lampetra japonica

The surface coat, ciliary process, and microvilli of the lamprey neuromast were examined with electron microscopy after tannic acid prefixation and lectin histochemistry. The neuromast was found to exist in the form of a dermal mound with a furrow in the middle. On the bottom of the furrow, the hair cell was characterized by a kinocilium and 15–20 stereocilia, arranged along the longitudinal axis of the furrow. Spanning structures were demonstrated between the kinocilium and stereocilia as well as between stereocilia. The surface coat, enhanced by tannic acid prefixation, was particularly rich over the surface of the supporting cell; by contrast, it was thin over the hair cell. Some lectins (PNA, GS-I, SBA, WGA) showed affinity to the surface coat of the supporting cell as well as the hair cell, and the others (RCA-I, MPA, ConA) showed affinity only to the supporting cell. These differences in the structure and affinities of the surface coat suggest an extracellular milieu highly specialized for the hair cell in this particular form of the mechanoreceptor.     

Astrocytes alter their polarity in organotypic slice cultures of rat visual cortex

The ultrastructure of astrocytes in an organotypic slice culture of the rat visual cortex was investigated using ultrathin sections and freeze-fracture replicas. After a culture period of 9–15 days, a glial scaffold formed that separated the bulk of the slice neuropil from the medium and the underlying plasma clot. However, the glial cells and processes did not build a dense barrier but allowed the outgrowth of neurites. A basal lamina covering the medium-oriented surface of the astrocytes was not found. In freeze-fracture replicas, orthogonal arrays of particles (OAP) were characteristic components of astrocytic membranes. The OAP density in membranes bordering the medium was 35±13 OAP/m², corresponding to 2.5% of this membrane area; the OAP density in membranes within the slice neuropil was 22±12 OAP/², corresponding to 1.4% of this membrane area. Although the difference was significant, it was greatly reduced when comparing OAP densities in endfoot and non-endfoot membranes in vivo. Another mode of polarity was recognized in astrocytes of the organotypic slice culture. In membranes of astrocytes bordering upon the medium, the density of non-OAP intramembranous particles (IMP) was clearly higher (1130±136 IMP/ m²) than in membranes of astrocytes in the center of the slice (700±172 IMP/m²). This pronounced IMP-related polarity was observed neither in vivo nor in cultured astrocytes. The present study suggests, together with data from the literature, that the distribution of astrocytic OAP across the cell surface is influenced by the existence of a basal lamina and neuronal activity, and that astrocytes possess a more remarkable plasticity of membrane structure than previously suspected.     

东方次睾吸虫电镜研究(吸虫纲:后睾科)V.雌性生殖器官

东方次睾吸虫雌性生殖器官（卵巢、输卵管、卵黄－输卵管、卵模、梅氏腺和子宫）透射电镜 观察。卵巢内有不同成熟期的生殖细胞,成熟初级卵母细胞有几个靠近核的核仁样小聚体和许多沿 质膜的皮质颗粒。首次发现并描述卵巢和输卵管接合处（卵巢壶腹）的超微结构。输卵管上皮为纤 毛状。梅氏腺仅一种类型膜状小体细胞,经有微管支持的细小管道穿过卵模将膜状小体排入卵模腔 内。在卵黄－输卵管和卵模中有精子,卵模和子宫中有受精卵、虫卵（扫描电镜）：大小 ２６. ０５× １１．４６－１３．５５μｍ,卵盖直径６．２６－６. ８９μｐ,卵壳表面布满膜状隆起。文中对卵巢和梅氏腺的超微 结构特点进行了讨论。     

Antioxidant Properties of Bromocriptine, a Dopamine Agonist

Abstract: It has been suggested that free radicals may adversely influence the pathogenesis of Parkinson's disease. We conducted this study to determine whether bro-mocriptine, an agent widely used for treating parkinsonism, possesses antioxidant effects. Bromocriptine scavenged superoxide produced from a superoxide generating system (hypoxanthine-xanthine oxidase) by the spin-trapping method using electron spin resonance. Bromocriptine had a strong scavenging effect on the 5,5-dimethyl-1-pyrroline- N -oxide hydroxide signal produced from Fenton's reaction. Bromocriptine also attenuated the stable free radical diphenyl- p -picrylhydrazyl signal. This drug inhibited the autooxidation of rat brain homogenates in a dose-dependent manner in vitro. Autooxidation of brain homogenates collected from rats treated with bromocriptine (2.5 mg/kg, i.p., daily for 3 days) was significantly reduced as compared with values in untreated rat homogenates. These observations suggest that bromocriptine is a free radical scavenger and a potent antioxidant.