Development of the preprophase band from random cytoplasmic microtubules in guard mother cells of Allium cepa L.

The organization of microtubule (MT) arrays in the guard mother cells (GMCs) of A. cepa was examined, focussing on the stage at which a longitudinal preprophase band (PPB) is established perpendicular to all other division planes in the epidermis. In the majority of young GMCs, including those seen just after asymmetric division, MTs are distributed randomly throughout the cortex and inner regions of the cytoplasm. Few MTs are associated with the nuclear surface. As the GMCs continue to develop, MTs cluster around the nucleus and a PPB appears as a wide longitudinal band. Microtubules also become prominent between the nucleus and the periclinal and transverse walls, while they decrease in number along the radial longitudinal walls. The PPB progressively narrows by early prophase, and a transversely oriented spindle gradually ensheaths the nucleus. These observations indicate that the initial, broad PPB is organized by a rearrangement of the random cytoplasmic array of MTs. Additional reorganization is responsible for MTs linking the nucleus and the cortex in the future plane of the cell plate, and for narrowing of the PPB.Abbreviations GMC guard mother cell - MT microtubule - PPB preprophase band     

A planar microtubule-organizing zone in guard cells of Allium: experimental depolymerization and reassembly of microtubules

The generation of the unique radial array of microtubules (MTs) in stomatal guard cells raises questions about the location and activities of relevant MT-organizing centers. By using tubulin immunofluorescence microscopy, we studied the pattern of depolymerization and reassembly of MTs in guard cells of Allium cepa L. Chilling at 0°C reduces the MTs to small remnants that surround the nuclear surface of cells in the early postcytokinetic stage, or form a dense layer along the central portion of the ventral wall in older guard cells. A rapid reassembly on rewarming restores either MTs extending from the nuclear surface randomly throughout the cytoplasm in very young cells, or an array of MTs radiating from the dense layer at the ventral wall later in development. A similar pattern of depolymerization and reassembly is achieved by incubation with 100 M colchicine followed by a brief irradiation with ultraviolet (UV) light. Incubation with 200 M colchicine leads to a complete depolymerization that leaves only a uniform, diffuse cytoplasmic fluorescence. Nonetheless, UV irradiation of developing guard cells induces the regeneration of a dense layer of MTs at the ventral wall. The layer is again positioned centrally along the wall, even if the nucleus has been displaced by centrifugation in the presence of cytochalasin D. Neither the regenerated layer nor the perinuclear MTs seen earlier are related to the staining pattern of serum 5051, which reportedly binds to centrosomal material in animal and plant cells. The results support the view that, soon after cytokinesis, a planar MT-organizing zone is established in the cortex along the central portion of the ventral wall, which then generates the radial MT array.Abbreviations GC guard cell - MT microtubule - MTOC microtubule-organizing center - UV ultraviolet To whom correspondence should be addressed.     

Regulation of the spatial order of cortical microtubules in developing guard cells ofAllium

The organization of microtubules (MTs) in the cortex of cells at interphase is an important element in morphogenesis. Mechanisms controlling the initiation of MTs and their spatial ordering, however, are largely unknown. Our recent study concerning the generation of a radial array of MTs in stomatal guard cells inAllium showed that the MTs initiate in a cortical MT-organizing zone adjacent to the ventral wall separating the two young guard cells (Marc, Mineyuki and Palevitz, 1989, Planta179, 516, 530). In an attempt to detect MT-ordering mechanisms separate from the sites of MT initiation, we now employ various drugs to manipulate the geometry and integrity of the ventral wall and thereby also the associated MT-organizing zone. In the presence of cytochalasin D the ventral wall is tilted away from its normal mid-longitudinal anticlinal alignment, while treatments with the herbicide chloroisopropyl-N-phenylcarbamate (CIPC) induce the formation of a branched ventral wall. Nonetheless, in either case the MTs still form a radial array, although this is asymmetric as it is centered in accordance with the misaligned or branched ventral wall. Since the MTs maintain their original course undisturbed as they extend beyond the abnormal ventral wall, there is no evidence for the presence of an inherent MT-ordering mechanism at locations remote from MT-initiation sites. Following treatments with caffeine, which abolishes the formation of the ventral wall, the MTs revert to a transversely oriented cylindrical array as in normal epidermal cells. Thus the presence of the ventral wall, and presumably also the associated MT-organizing zone, is essential for the establishment of the radial array. The MT-organizing zone is therefore involved not only in the initiation of MTs, but also in determining their spatial order throughout the cell cortex. We thank Drs. Richard J. Cyr and Yoshi Mineyuki for providing valueable suggestions during the course of this work, and Ms. Elizabeth Bruce printing some of the figures. This research was supported by Funds from the National Science Foundation grants DCB-8703292 to B.A.P. and DCB-8803286 to B.A.P. and J.M.     

gamma-Tubulin and microtubule organization in plants

In animal cells, microtubule assembly is usually initiated at one specialized structure, the centrosome. By contrast, in plant cells, microtubule assembly begins at a variety of locations within the cell. A member of the tubulin gene family, gamma-tubulin, is localized to the centrosome in animal cells and is important in the assembly of microtubules in vivo. Recent reports have identified gamma-tubulin genes in plants and have described the complex intracellular distribution of the encoded polypeptides. Here, Harish Joshi and Barry Palevitz comment upon how this information may help elucidate the organizing principles of the complex arrays of microtubules in plant cells.     

Fluorescence staining of living cells with fluorescamine

Summary The interaction of fluorescamine with living plant and animal cells was investigated to determine which subcellular structures and molecular species might react with the dye and to assess its effects on cell viability and function.Plasma and nuclear membranes ofXenopus erythrocytes, mitochondria of sea urchin sperm, growing apices of Timothy root hairs, and various organelles ofNitella andEuglena were labelled as judged by fluorescence microscopy. Cytoplasmic fluorescence was particulate inNitella and easily displaced by moderate centrifugal fields in sea urchin eggs. Chloroplasts and nuclei isolated from cells labelledin vivo exhibited fluorescamine dependent fluorescence.Reaction seemed to have little or no effect on cell viability (Euglena) photoautotrophic growth (Euglena), cell motility (sperm), fertilizability (sperm or egg), embryonic development (sea urchin), or cytoplasmic streaming (Nitella, Timothy).Quantitative fluorometric analysis of thein vivo reactants in sperm indicated a reaction preference for phospholipid over protein compared to control cells dissociated in SDS prior to labelling. The bulk of labelled lipid was phosphatidylethanolamine.These results suggest that fluorescamine is a true vital dye which can label the cell surface as well as penetrate deeply within cells to label a variety of organelles. The distribution of fluorescence and results of chemical analysis suggest thatin vivo the dye may preferentially react with membrane.     

中国西北沙漠夜间活动的东鳖甲属昆虫二新种(鞘翅目:拟步甲科:漠甲亚科)

记述中国西北地区东鳖甲属2新种:巴丹东鳖甲A.badainica Ba,Ren&Liu sp.nov.和古尔班东鳖甲A.gurbantunggutica Ba&Ren sp.nov.,提供了主要鉴别特征和形态图,并简要讨论了其昼夜活动规律.     

Haemosporidian Parasites of Antelopes and Other Vertebrates from Gabon,Central Africa

Re-examination, using molecular tools, of the diversity of haemosporidian parasites (among which the agents of human malaria are the best known) has generally led to rearrangements of traditional classifications. In this study, we explored the diversity of haemosporidian parasites infecting vertebrate species (particularly mammals, birds and reptiles) living in the forests of Gabon (Central Africa), by analyzing a collection of 492 bushmeat samples. We found that samples from five mammalian species (four duiker and one pangolin species), one bird and one turtle species were infected by haemosporidian parasites. In duikers (from which most of the infected specimens were obtained), we demonstrated the existence of at least two distinct parasite lineages related to Polychromophilus species (i.e., bat haemosporidian parasites) and to sauropsid Plasmodium (from birds and lizards). Molecular screening of sylvatic mosquitoes captured during a longitudinal survey revealed the presence of these haemosporidian parasite lineages also in several Anopheles species, suggesting a potential role in their transmission. Our results show that, differently from what was previously thought, several independent clades of haemosporidian parasites (family Plasmodiidae) infect mammals and are transmitted by anopheline mosquitoes.     

Molecular basis of ion permeability in a voltage‐gated sodium channel

Voltage‐gated sodium channels are essential for electrical signalling across cell membranes. They exhibit strong selectivities for sodium ions over other cations, enabling the finely tuned cascade of events associated with action potentials. This paper describes the ion permeability characteristics and the crystal structure of a prokaryotic sodium channel, showing for the first time the detailed locations of sodium ions in the selectivity filter of a sodium channel. Electrostatic calculations based on the structure are consistent with the relative cation permeability ratios (Na⁺ ≈ Li⁺ ≫ K⁺, Ca²⁺, Mg²⁺) measured for these channels. In an E178D selectivity filter mutant constructed to have altered ion selectivities, the sodium ion binding site nearest the extracellular side is missing. Unlike potassium ions in potassium channels, the sodium ions in these channels appear to be hydrated and are associated with side chains of the selectivity filter residues, rather than polypeptide backbones.