银杏(Ginkgo biloba)叶表皮特征及其气孔的发育

通过光学显微镜和扫描电子显微镜,对离析和未离析的、成熟的和刚开始发育的银杏叶表皮进行了研究.表皮基本特征:两面生气孔型,但气孔主要分布在下表皮,上表皮气孔的数目和分布因个体而异;气孔器为单唇单环式,围绕每个气孔的副卫细胞数目多为5～6个;副卫细胞的平周壁明显加厚,具乳突状突起,拱盖着下陷的保卫细胞;偶有双气孔发生;上表皮厚于下表皮;表皮细胞可明显分为叶脉区和脉间区.角质外蜡质层:在高倍扫描电子显微镜下,管状的蜡质晶体交错覆盖在叶片的外表面,还观察到有些管状的蜡质晶体呈分叉状态.气孔的发育:通过我们的观察,认为银杏气孔的发生属于典型的周源型, 即副卫细胞与保卫细胞各自发生于不同的母细胞,而不是前人报道的中--周型起源.     

The hunt for plant nitric oxide synthase (NOS): Is one really needed?

Nitric oxide (NO) production is associated with many physiological situations in plants, and NO is a key signaling molecule throughout the lifespan of a plant. The complexity of the underlying signaling events are just starting to be unraveled. The basis for nitric oxide signaling, the production of the signaling molecule itself, is far from understood in plants. While in animals, three homologous NO synthases (NOS) isoforms have been identified, yet in higher plants no corresponding enzymes are known so far. More than half a dozen NO productive reactions have been observed in plants but only few of them have been thoroughly investigated. It remains to be elucidated how these parts act together to form the sophisticated NO signaling network observed in plants.     

Is there an urban effect in alien plant invasions?

Cities are known to be extraordinarily rich in alien plant species compared to rural environments. This is related to specific attributes of urban areas including the availability of natural resources and habitats (namely geological substrates and land cover), the dispersal pathways and associated propagule pressure due to trade and traffic, and the proximity many urban hubs have to rivers. Here we explored how richness and proportions of alien species introduced after the discovery of the Americas (so-called neophytes), can be explained by environmental covariates along the urbanization gradient from very rural to very urbanized grid cells. We tested whether there is a specific urban effect, either as an interaction effect of urbanized areas that changes these general relationships, or if there is an effect due to specific urban conditions. We found that the environmental covariates explaining richness as well as proportions of neophytes remain largely the same across the rural–urban gradient. There is, however, an effect of urbanized area on neophyte species richness and proportions, which also incorporates strictly urban conditions. Rivers, roads and railroads contribute disproportionately less to the increase of neophyte species diversity in more urbanized areas, which might be due to the already higher number of neophytes in cities. We argue that the conditions determining neophyte richness in cities are not fundamentally different from those in rural environments, but extend on the same environmental axis, i.e. having different positions along the gradient towards the upper end.     

Purification and Characterization of a Co(II)-Sensitive α-Mannosidase from Ginkgo biloba Seeds

An α-mannosidase was purified from developing Ginkgo biloba seeds to apparently homogeneity. The molecular weight of the purified α-mannosidase was estimated to be 120 kDa by SDS–PAGE in the presence of 2-mercaptoethanol, and 340 kDa by gel filtration, indicating that Ginkgo α-mannosidase may function in oligomeric structures in the plant cell. The N-terminal amino acid sequence of the purified enzyme was Ala–Phe–Met–Lys–Tyr–X–Thr–Thr–Gly–Gly–Pro–Val–Ala–Gly–Lys–Ile–Asn–Val–His–Leu–. The α-mannosidase activity for Man₅GlcNAc₁ was enhanced by the addition of Co²⁺, but the addition of Zn²⁺, Ca²⁺, or EDTA did not show any significant effect. In the presence of cobalt ions, the hydrolysis rate for pyridylaminated Man₆GlcNAc₁ was significantly faster than that for pyridylaminated Man₆GlcNAc₂, suggesting the possibility that this enzyme is involved in the degradation of free N-glycans occurring in developing plant cells (Kimura, Y., and Matsuo, S., J. Biochem., 127, 1013–1019 (2000)). To our knowledge, this is the first report showing that plant cells contain an α-mannosidase, which is activated by Co²⁺ and prefers the oligomannose type free N-glycans bearing only one GlcNAc residue as substrate.     

Is your initiator really necessary?

There is little hard evidence for the involvement of specific genotoxic initiators in the pathogenesis of the common carcinoma. Recent findings suggest that sporadic carcinogenesis is a dynamic and probabilistic process which requires a critical mass of abnormal cells for its expression, and that this requirement may distinguish the evolution of carcinomas from that of paediatric or haematologic malignancies. The proposal that specific carcinogens are neither necessary nor sufficient for tumourigenesis is consistent with the growing realization that aberrant expression of specific oncogenes is neither necessary nor sufficient for cellular transformation. These new perspectives have major implications for basic research strategy and public health policy.     

Heme Oxygenase 1-Mediated Neurogenesis Is Enhanced by Ginkgo biloba (EGb 761®) After Permanent Ischemic Stroke in Mice

Stroke is the fourth leading cause of death and a major cause of disability in stroke survivors. Studies have underlined the importance of repair mechanisms in the recovery phase of stroke. Neurogenesis in response to brain injury is one of the regeneration processes that, if enhanced, may offer better stroke treatment alternatives. Previously, we have demonstrated antioxidant, neuritogenic, and angiogenic properties of Ginkgo biloba/EGb 761® (EGb 761) in different mouse models of stroke. In the present study, we were interested to study whether EGb 761 could protect mice from permanent middle cerebral artery occlusion (pMCAO) and enhance neurogenesis. EGb 761 pre- and posttreated mice had lower infarct volume and improved motor skills with enhanced proliferation of neuronal stem/progenitor cells (NSPCs) at 24 h and 7 days posttreatment. Netrin-1 and its receptors (DCC and UNC5B) that mediate axonal attraction and repulsion were observed to be overexpressed in NSPCs only, implying that netrin-1 and its receptors might have partly played a role in enhanced neurogenesis. Interestingly, in heme oxygenase 1 knockout mice (HO1^?/?), neurogenesis was significantly lower than in vehicle-treated mice at day 8. Furthermore, EGb 761 posttreated mice also demonstrated heme oxygenase 1 (HO1)-activated pathway of phosphorylated glycogen synthase kinase 3 α/β (p-GSK-3 α/β), collapsin response mediator protein 2 (CRMP-2), semaphorin3A (SEMA3A), and Wnt, suggesting probable signaling pathways involved in proliferation, differentiation, and migration of NSPCs. Together, these results propose that EGb 761 not only has antioxidant, neuritogenic, and angiogenic properties, but can also augment the repair and regeneration mechanisms following stroke.     

Is dynamin really a 'pinchase'?

The motivation for this article was a recent conversation with an author of a major cell-biology textbook who was gratified that the problem of ?pinching off? membrane vesicles from donor membranes had been solved.It was now known, the author claimed, that the large GTPase dynamin was a ?pinchase? severing the necks of budding vesicles.We are concerned that this appealing speculation has been prematurely elevated to cell-biological dogma.Furthermore, by seeing dynamin exclusively as a pinchase we might fail to recognize alternative functions.In this article, we review briefly the evidence that dynamin is a pinchase, discuss some problems with that speculation and show that other possible functions for dynamin may be at least as appealing.     

Is internucleosomal DNA fragmentation an indicator of programmed death in plant cells?

Specific DNA fragmentation into oligonucleosomal units occurs during programmed cell death (PCD) in both animal and plant cells, usually being regarded as an indicator of its apoptotic character. This internucleosomal DNA fragmentation is demonstrated in tobacco suspension and leaf cells, which were killed immediately by freezing in liquid nitrogen, and homogenization or treatment with Triton X-100. Although these cells could not activate and realize the respective enzymatic processes in a programmed manner, the character of DNA fragmentation was similar to that in the cells undergoing typical gradual PCD induced by 50 microM CdSO4. This internucleosomal DNA fragmentation was connected with the action of cysteine proteases and the loss of membrane, in particular tonoplast, integrity. The mechanisms of DNase activation in the rapidly killed cells, hypothetical biological relevance, and implications for the classification of cell death are discussed.     

Is torso soft tissue motion really an artefact within breast biomechanics research?

For rigid body POSE estimation, any relative movement of the tracking markers on a segment is often referred to as an artefact; however this may be an important part of the signal within breast biomechanics. This study aimed to quantify differences in breast range of motion when calculated relative to the torso segment using either direct or segment optimised POSE estimation algorithms. Markers on the torso and right nipple were tracked using infrared cameras (200 Hz) during five running gait cycles in three breast support conditions (no bra, everyday bra and sports bra). Multiplanar breast range of motion was calculated relative to the torso segment using two POSE estimation algorithms. First, the torso segment was defined using direct POSE estimation (direct). Second, while standing stationary in the anatomical position; the positional data of the torso markers were used to construct the torso using segment optimised POSE estimation (optimised). The torso segment length defined using direct POSE estimation changed significantly by 3.4 cm compared to that of the segment optimisation POSE estimation in the no bra condition. Subsequently, superioinferior breast range of motion was significantly greater (p<0.017) when calculated using direct POSE estimation, within each of the three breast support conditions. Segment optimisation POSE estimation is recommended to minimise any differences in breast motion associated with intra segment deformation between physical activity types. However, either algorithm is recommended when evaluating different breast support garments, as a correctly fitted bra does not cause the torso markers to move relative to each other.     

Is the Guadeloupean racoon (Procyon minor) really an endemic species? New insights from molecular and chromosomal analyses

The Guadeloupean racoon has been chosen as the emblematic species of the Parc National de Guadeloupe because of its supposed endemic specificity. However, its taxonomic position is not clearly defined. At what period did this animal colonize Guadeloupe and how it reached the island remain unsolved questions. To clarify these points, insular and continental individuals (Procyon lotor), coming from five localities and belonging to three subspecies, were compared using molecular (sequencing of a 294-bp of the left domain of the mtDNA control region) and chromosomal (C, G and R karyotypes) analyses. Genetic distance between the Guadeloupean racoon and lotor subspecies from Virginia and Maryland was very short (mean sequence divergence between haplotypes equals to 1.46%). A four times higher distance was found between P. l. lotor and P. l. pallidus, a continental subspecies inhabiting Arizona than between P. l. lotor and Procyon minor. A neighbour-joining phenogram is proposed; the Guadeloupean haplotype is on a branch close to the one clustering P. l. lotor from the East coast whereas the haplotype from Arizona diverged earlier. These results strongly suggest that the Guadeloupean racoon is included in the P. lotor species. Moreover, no differences were found between P. lotor and P. minor karyotypes, again suggesting a high genetic homogeneity between the two taxa. Furthermore, comparison of the control region variability within Procyon with intra- and interspecific variability observed in other Carnivores, clearly strengthens the hypothesis that P. minor is conspecific with P. lotor. These results imply that the taxonomic status of the Guadeloupean racoon should be revised. In a biogeographic perspective, it is suggested that the racoon has been recently introduced in Guadeloupe by man with individuals coming from the east coast of the USA. The consequences of these results for conservation of the racoon in Guadeloupe, and more generally, the definition and the use of the subspecies as a unit of conservation are discussed.     

Is 2,3-butanedione monoxime an effective inhibitor of myosin-based activities in plant cells?

Summary The effectiveness of 2,3-butanedione monoxime (BDM) as an inhibitor of plant myosins has been investigated. Three myosin-dependent motility phenomena in plants, namely cytoplasmic streaming inChara corallina, light-dependent chloroplast repositioning inElodea sp., and brefeldin A(BFA)-induced Golgi membrane dynamics in wheat (Triticum aestivum L. cv. Kite) roottip cells were investigated. All three processes were inhibited by the sulfhydryl-modifying agent N-ethylmalemide (NEM), indicating the probable involvement of myosin as the motor protein in each case. However, none of these myosin-dependent processes were inhibited by BDM at concentrations as high as 20 mM in some instances. These results therefore question the general usefulness of BDM as an inhibitor of myosin-based activities in plant cells.     

Is stress really all that important?

There is growing concern in many parts of the world that fertility of dairy cattle is reducing as milk yields increase. Stress could be one important cause. As an example, fertility is lower after caesarian operations. Delayed uterine involution after dystocia is associated with abnormal ovarian cyclicity and prolonged intervals to the next pregnancy. There is a greater reduction in fertility as the clinical conditions of lameness, milk fever or mastitis worsen. Changes in social groupings greatly increase the number of inseminations required per pregnancy. Transport reduces the number of CL after superovulation, and can interfere with pregnancy rates after estrous synchronization. Embryos collected from heat-stressed donors are less viable and have delayed trophoblast function. Human-animal interactions influence stress-responses in cattle--the behavior of stockman and embryo transfer personnel could affect success. Putting aside financial aspects, exposure of an animal to avoidable stress compromises welfare, whether application of biotechnology is involved or not. The fact that stressors can be deleterious to such an important function as reproduction, emphasizes that stress is very important and should be minimized whenever possible.     

Is Phillyrea angustifolia L. (Oleaceae) an androdioecious species?

LEPART, J. & DOMMEE B., 1992. Is Phillyrea angustifolia L. (Oleaceae) an androdioecious species? Observations during two or three years on three natural populations of Phillyrea angustifolia growing in contrasting environments in southern France show that two distinct phenotypes occur in approximately equal proportions: hermaphrodites, which produce pollen and seeds, and males, which produce pollen only. The populations studied are thus morphologically androdioecious. Biometric investigation of the two morphs shows that they are clearly distinguished by (1) the shape of the stigma and (2) the ovary which is well developed in hermaphrodites and aborted in males. Neither size of anthers and corolla, nor pollen germination, differ between the two sexes. In the Camargue, where P. angustifolia is presently an invader, controlled crosses between hermaphrodites (selfing and inter-individual) are partially successful. In contrast, such crosses are sterile in the well-established population of the La Gardiole. Hence the Camargue population appears to be functionally androdioecious and La Gardiole functionally dioecious. This breeding system is particularly puzzling, since the occurrence of anemogamy and possible selfing do not fit classical explanations of androdioecy. The ability of hermaphrodites to be functionally male and female could be particularly adaptive in founding populations. Since functional hermaphroditism occurs in expanding populations of the Camargue population, we consider that the androdioecy of P. angustifolia could be a kind of leaky dioecism.     

Is 2,3-butanedione monoxime an effective inhibitor of myosin-based activities in plant cells?

The effectiveness of 2,3-butanedione monoxime (BDM) as an inhibitor of plant myosins has been investigated. Three myosin-dependent motility phenomena in plants, namely cytoplasmic streaming in Chara corallina, light-dependent chloroplast repositioning in Elodea sp., and brefeldin A(BFA)-induced Golgi membrane dynamics in wheat (Triticum aestivum L. cv. Kite) root-tip cells were investigated. All three processes were inhibited by the sulfhydryl-modifying agent N-ethylmalemide (NEM), indicating the probable involvement of myosin as the motor protein in each case. However, none of these myosin-dependent processes were inhibited by BDM at concentrations as high as 20 mM in some instances. These results therefore question the general usefulness of BDM as an inhibitor of myosin-based activities in plant cells.     

Is immunity to malaria really short-lived?

Protection against Plasmodium falciparum malaria is usually considered to be the cumulative product of repeated exposure to parasites, and thus a function of age, in endemic areas. The recent outbreak of malaria in the central highlands of Madagascar gave Philippe Deloron and Claire Chougnet the opportunity to compare the incidence of malaria in children and young adults exposed to malaria for the first time, with that in older adults who spent their childhood in the study area before malaria control was introduced. Protection, as well as immune responses to two major P. falciparum antigens, was not related to age. Individuals older than 40 years were more protected than were younger adults. This increased protection was probably due to immunological memory.     

Is DNA really a double helix?

Do the two chains of the DNA molecule coil round one another plectonemically ? If so, what is the approximate value of Lk (the linking number) for any closed, circular DNA molecule? Experiments using gel electrophoresis have shown that supercoiled DNA molecules usually migrate in a series of discrete bands. The only tenable explanation for this quantized behavior is that the molecules in one band all have the same value of Lk and that this value differs by unity from that of the adjacent bands. Various experiments in which circular DNA is unwound by known amounts show that (given this assumption) Lk for relaxed DNA is very roughly equal to $\text{N}\text{10}$ (where N is the number of base-pairs), as expected from the classical double helix.The original model for the double helix was right-handed. The experimental evidence for this feature is suggestive but not yet completely compelling.