The formation and distribution of ice within dormant and deacclimated peach flower buds

Abstract A freeze-fixation technique was used to examine the distribution of ice crystals and the pattern of freezing in peach flower buds. In dormant buds, ice crystals formed at localized sites within the bud axis and scales. Ice crystal formation disrupted tissues and mechanical injury from repetitive freezethaw cycles was apparent. There was evidence of ice formation in the floral organs of dormant buds exposed to ?25°C but none observed in buds exposed to either ?5 or ?10°C. The distribution of ice crystals was different in deacclimated buds. In addition to large ice crystals within the subtending bud axis and scales, evidence of large crystals within the developing floral organs was noted. These crystals were most prominent in the lower portions of the developing flower and peduncle, and caused a separation of the epidermal layer from adjacent cells. The distribution of ice crystals within both dormant and deacclimated peach flower buds corroborated the results of previous thermal analysis experiments.     

The innermost chorionic layer of Drosophila. I. The role of chorin octamers in the formation of a family of interdigitating crystalline plates

The innermost chorionic layer (ICL) within egg shells of Drosophila melanogaster is composed of thin, abutting three-dimensional crystalline plates which form a closed, membrane-like sheath. Collectively, the crystals within the sheath appear to form a family of related three-dimensional crystals in space group C222; however, specimens prepared for electron microscopy are actually two-dimensional crystals in c222. The projected structures of the negatively stained crystals have been studied by minimal dose electron microscopy employing image reconstruction methods. Thin sections indicate that unit cells within the ICL are composed of paired layers; top and bottom layers are related by centrally located 2-fold axes, aligned parallel to the surface of the ICL. The most probable structural unit of the crystals is a tetramer of chorin dimers with a point group symmetry of 222, which is denoted a chorin octamer. Projection maps were computed from average transforms of two-dimensional crystals for delta (the primitive unit cell angle) equal to 84 degrees, 90 degrees and 97 degrees (+/- 1.5 degrees). The maps indicate that the molecular transitions responsible for the observed family of crystals involve concerted intramolecular rearrangements about molecular 2-fold axes. The significance in vivo of the family of crystals within the ICL is not known; however, structural considerations suggest that the observed polymorphism may reflect one facet of an intrinsic bonding flexibility of the ICL octamer that may play a role in the formation of interplate junctions and the assembly of a continuous closed sheath. The ICL may therefore serve as a structural bridge between the vitelline membrane-wax layer and the endochondrial floor, allowing the larva to shed the inner egg shell layers during hatching.     

Prismatic dentine in the Australian lungfish, Neoceratodus forsteri (Osteichthyes: Dipnoi)

The Australian lungfish, Neoceratodus forsteri, has a dentition consisting of enamel, mantle dentine and bone, enclosing circumdenteonal, core and interdenteonal dentines. Branching processes from cells that produce interdenteonal dentine leave the cell surface at different angles, with collagen fibrils aligned parallel to the long axis of each process. In the interdenteonal dentine, crystals of calcium hydroxyapatite form within fibrils of collagen, and grow within a matrix of non-collagenous protein. Crystals are aligned parallel to the cell process, as are the original collagen fibrils. Because the processes are angled to the cell surface, the crystals within the core or interdenteonal dentine are arranged in bundles set at angles to each other. Apatite crystals in circumdenteonal dentine are finer and denser than those of the interdenteonal dentine, and form outside the fibrils of collagen. In mature circumdenteonal dentine the crystals of circumdenteonal dentine form a dense tangled mass, linked to interdenteonal dentine by isolated crystals. The functional lungfish tooth plate contains prisms of large apatite crystals in the interdenteonal dentine and masses of fine tangled crystals around each denteon. This confers mechanical strength on a structure with little enamel that is subjected to heavy wear.     

Magnesium content within the skeletal architecture of the coral Montastraea faveolata: locations of brucite precipitation and implications to fine-scale data fluctuations

Small portions of coral cores were analyzed using a high-resolution laser ablation inductively coupled plasma mass spectrometer (LA ICP-MS) to determine the geochemical signatures within and among specific skeletal structures in the large framework coral, Montastraea faveolata. Vertical transects were sampled along three parallel skeletal structures: endothecal (septal flank), corallite wall, and exothecal (costal flank) areas. The results demonstrate that trace element levels varied among the three structures. Magnesium (Mg) varied among adjacent structures and was most abundant within the exothecal portion of the skeleton. Scanning electron microscopy (SEM) revealed the presence of hexagonal crystals forming thick discs, pairs or doublets of individual crystals, and rosettes in several samples. High Mg within these crystals was confirmed with energy dispersive spectroscopy (EDS), infrared spectrometry, and LA ICP-MS. The chemical composition is consistent with the mineral brucite [Mg(OH₂)]. These crystals are located exclusively in the exothecal area of the skeleton, are often associated with green endolithic algae, and are commonly associated with increased Mg levels found in the adjacent corallite walls. Although scattered throughout the exothecal, the brucite crystals are concentrated within green bands where levels of Mg increase substantially relative to other portions of the skeleton. The presence and locations of high-Mg crystals may explain the fine-scale fluctuations in Mg data researchers have been questioning for years.     

The structure and mitotic behaviour of a nuclear inclusion in a fern

Summary A study has been made of the structure and behaviour during mitosis of a crystalline inclusion within cell nuclei of roots of Dryopteris filix-max. The inclusion within the interphase nucleus is an aggregate of randomly oriented crystals. All the crystals are similar, and consist of a cubic array of particles of unit spacing approximately 100 Å. During mitosis, the inclusions are eliminated from the nucleoplasm at prometaphase. The crystals reappear within the nucleus at early interphase by a process of random crystallisation from a preformed mass of amorphous material. The results are discussed in the light of previous work on nuclear inclusions in plants and of current theories of the mode of action of microtubules.     

Two‐dimensional crystals of carboxysome shell proteins recapitulate the hexagonal packing of three‐dimensional crystals

Bacterial microcompartments (BMCs) are large intracellular bodies that serve as simple organelles in many bacteria. They are proteinaceous structures composed of key enzymes encapsulated by a polyhedral protein shell. In previous studies, the organization of these large shells has been inferred from the conserved packing of the component shell proteins in two‐dimensional (2D) layers within the context of three‐dimensional (3D) crystals. Here, we show that well‐ordered, 2D crystals of carboxysome shell proteins assemble spontaneously when His‐tagged proteins bind to a monolayer of nickelated lipid molecules at an air–water interface. The molecular packing within the 2D crystals recapitulates the layered hexagonal sheets observed in 3D crystals. The results reinforce current models for the molecular design of BMC shells.     

Three-dimensional spatial relationship between the collagen fibrils and the inorganic calcium phosphate crystals of pickerel (Americanus americanus) and herring (Clupea harengus) bone

High-voltage (1.0 MV) electron microscopy and stereomicroscopy, electron probe microanalysis, electron diffraction and three-dimensional computer reconstruction, have been used to examine the spatial relationship between the inorganic crystals of calcium phosphate and the collagen fibrils of pickerel and herring bone. High-voltage stereo electron-micrographs were obtained of cross-sections of the cylinder-shaped intramuscular bones in uncalcified regions, in regions where only one or only several crystals had been deposited in some of the fibrils, and in successive sections containing progressively more mineral crystals until the stage of full mineralization was reached. High-resolution electron probe microanalysis confirmed that the electron-dense particles contained calcium and phosphorus. In the earliest stages of mineralization and progressing throughout the mineralization process, the crystals are located only within the collagen fibrils; crystals are not observed free in the extracellular spaces between collagen fibrils. The progressive increase in the mass of mineral deposited in the bone tissue with time occurs, essentially, completely within the collagen fibrils including the stage of full mineralization. At this stage, cross-sectional profiles of collagen fibrils are completely obliterated by mineral. A small number of crystals that are located on or close to the surface of the fibrils appear to extend a very short distance into the spaces between the fibrils. These ultrastructural observations of the very onset of calcification in which nucleation of the calcium phosphate crystals is clearly shown to begin within specific volumes of collagen fibrils, and of the subsequent temporal and spatial sequences of this phenomenon, which shows that calcification continues wholly within the collagen fibrils until maximum calcification is achieved, add important information on the basic physical chemical mechanism of the calcification and the structural elements that are involved. The spatial and temporal independence of the sites where mineralization is initiated establishes that such ultrastructural locations within individual collagen fibrils represent independent, physical chemical nucleation loci. The findings are totally inconsistent with the proposal that crystals must first be deposited in matrix vesicles, or other components such as mitochondria, and subsequently released and propagated in the interfibrillar space, until they eventually reach and impregnate the hole zone regions of the collagen fibrils. Three-dimensional computer reconstruction of serial transverse and longitudinal sections demonstrates periodic swellings along the collagen fibrils, corresponding to the hole zone region of their axial period as mineralization proceeds.(ABSTRACT TRUNCATED AT 400 WORDS)     

Developmental features of calcium oxalate crystal sand deposition inBeta vulgaris L. Leaves

Summary Sugar beet (Beta vulgaris L.) leaf has a layer of cells extended laterally between the palisade parenchyma and spongy mesophyll that develop numerous small crystals (crystal sand) within their vacuoles. Solubility studies and histochemical staining indicate the crystals are calcium oxalate. The crystals are deposited within the vacuoles early during leaf development, and at maturity the cells are roughly spherical in shape and 2 to 3 times larger than other mesophyll cells. Crystal deposition is preceeded by formation of membrane vesicles within the vacuole. The membranes are synthesizedde novo in the vacuole and have a typical trilaminate structure as viewed with the TEM. The membranes are formed within paracrystalline aggregates of tubular particles (6–8nm outer diameter) as membrane sheets, but are later organized into chambers or vesicles. Calcium oxalate is then precipitated within the membrane chambers. The tubular particles involved in membrane synthesis are usually present in the vacuoles of mature crystal cells, but in very small amounts.     

Comparative Microscopical Studies on the Patterns of Calcium Oxalate Distribution in the Needles of Various Conifer Species

The distribution of calcium oxalate crystals in various conifer needles is visualized by light and electron microscopy. Such crystals occur (1) in the vascular bundle, either intracellularly in the xylem or phloem parenchyma, or extracellularly within the radial phloem walls; (2) extracellularly on the outside of the walls of mesophyll cells which face the intercellular spaces; (3) and finally as numerous small crystals within the cell walls of the epidermal cells, especially in the cuticular layer. The development and distribution of these apoplastic crystals is described in detail. Some hypotheses are finally presented for interpretations of these unusual patterns of the crystallization of Ca-oxalate outside the vacuole. Possible evolutionary aspects of this feature among the different conifer families are also discussed.     

红豆草中含晶细胞的形态学研究

红豆草（Ｏｎｏｂｒｙｃｈｉｃｖｉｃｉａｅｆｏｌｉａｓｃｏｐ．）植株的所有器官中都分布有含晶细胞,其结晶的类型主要为棱晶,此外还有砂晶。在营养器官中,含棱晶的细胞主要分布在维管组织之中或外围。横切面上,棱晶则几至几十块纵列成行存在,且常伴生于韧皮纤维旁,但每块棱晶各有一分室隔开;在茎的表皮下偶有与大型粘液细胞伴生的砂晶。花萼的表皮中偶有棱晶,花瓣表皮及雄蕊药隔中有砂晶;子房壁内表皮下一层细胞逐渐发育成含棱晶的连续细胞,同时子房维管组织中也形成大量棱晶。分析表明,结晶成分为草酸钙。     

Hexagonal columnar liquid crystal in the cells secreting spider silk

The liquid crystallinity of spider dragline silk dope is thought to be important for both the spinning process and the extreme mechanical properties of the final thread. Although the formation of the liquid crystalline units is poorly understood, it has been suggested that spider silk proteins are secreted in a random coil and then aggregate end-to-end into rod-shaped units to form supramolecular liquid crystals. However, evidence presented here from transmission electron microscopy indicates that coat protein of the dragline silk of a Nephila spider is stored as hexagonal columnar liquid crystals within the intracellular secretory vesicles. This implies that this component is already folded into short rods within the gland cells and forms molecular rather than supramolecular liquid crystals.     

Two-dimensional crystalline sheets of Bacillus stearothermophilus 50S ribosomal particles.

Two-dimensional crystalline sheets of the large ribosomal subunit from Bacillus stearothermophilus have been obtained using a slightly modified procedure to that for growing three-dimensional crystals of the same material. The crystalline subunits are packed within monolayers in a relatively small unit cell, the dimensions of which are closely related to those observed for two forms of the three-dimensional crystals. The packing symmetry is p121, and the optical diffraction patterns of micrographs of negatively stained crystals extend to approximately 3.0 nm.     

High-resolution electron-microscopic study of the relationship between human enamel and dentin crystals at the dentinoenamel junction

The development of dentin and of enamel share a common starting locus: the dentinoenamel junction (DEJ). In this study the relationship between enamel and dentin crystals has been investigated in order to highlight the guiding or modulating role of the previously mineralized dentin layer during enamel formation. Observations were made with a high-resolution electron microscope and, after digitalization, image-analysis software was used to obtain digital diffractograms of individual crystals. In general no direct epitaxial growth of enamel crystals onto dentin crystals could be demonstrated. The absence of direct contact between the two kinds of crystals and the presence of amorphous areas within enamel particles at the junction with dentin crystals were always noted. Only in a few cases was the relationship between enamel and dentin crystals observed, which suggested a preorganization of the enamel matrix influenced by the dentin surface structure. This could be explained either by the existence of a proteinaceous continuum between enamel and dentin or by the orientation of enamel proteins by dentin crystals.     

Direct assignment of the absolute configuration of molecules from crystal morphology

A method for direct assignment of the absolute configuration of molecules and the absolute structures of polar crystals, independent to that of Bijvoet, is described. The method correlates between the two-dimensional packing arrangement of specific faces, that delineate crystals during their growth and dissolution, with molecules present in the environment. The structural information stored in these faces is transferred to "tailor-made" molecules added to the solvent by controlled morphological changes induced to the growing crystals and by the creation of etch pits at specific crystal faces during their dissolution. In addition, the "tailor-made" molecules are occluded enantioselectively as guests within specific sectors of the host crystals. The method is illustrated for a variety of molecules and crystals including the assignment of the absolute configuration of several alpha-amino acids as "tailor-made" additives in centrosymmetric crystals of glycine and serine, for the absolute structure of polar crystals of sugars and alpha-amino acids and consequently the absolute configuration of molecules packed in such crystals.     

Distribution of elements on tobacco trichomes and leaves under cadmium and sodium stresses

When tobacco (Nicotiana tabacum) plants are exposed to toxic level of cadmium (0.2 mM Cd), their trichomes actively excrete crystals (Choi et al., 2001). In this study, we investigated the distribution of Cd and NaCI on trichomes and leaf surfaces. Energy dispersive x-ray (EDX) analysis revealed that, under toxic Cd stress, crystals exudated from the trichomes contained high amounts of Ca, Mg, and Cd, as well as low levels of P, S, and Mn. Electron spectroscopic imaging (ESI) from trichomes and attached crystals showed that these crystals emitted denser radiation energy for Ca and Cd than did the head cells of the trichomes. However, no Cd was detected on the trichome surface itself or within the leaf epidermis. In contrast, treatment with salt (NaCI) did not stimulate crystal formation; instead, it induced the abnormal expansion of trichome cells. Although Na was not accumulated within the crystals, a considerable amount of both Na and CI was sequestered within the stalk cells of the long trichomes. Therefore, we believe that tobacco trichomes play an important role in Cd crystal exudation through crystallization, but that, under NaCI stress, the long trichomes sequester those elements within their stalks.     

The formation of intracellular crystals in midgut glands of Limnoria lignorum

Certain morphological features of intracellular crystal formation within the midgut glands of Limnoria lignorum (Rathke) have been studied with the electron microscope and cytochemical methods. A correlation has been established between Golgi membranes and formation of the crystals. The Prussian blue reaction reveals quantities of iron localized in the intracellular crystals and in small granular structures seen in the apical region of the cells. These granules can be identified as accumulations of Golgi membranes, with which iron-containing particles are associated. When these membrane configurations are studied with the electron microscope, they can be classified and arranged in an assumed sequence which is thought to represent successive stages in the development of crystals. As the membrane systems become progressively specialized, increasing accumulations of dense granular material appear within their interstices. This material is rich in iron and probably represents the component responsible for the positive Prussian blue reaction. This material also appears to be a precursor substance for iron-containing protein molecules which are synthesized and arranged to make up the crystals. These iron-containing molecules are first deposited in orderly array as double rows of dense particles on certain internal membranes of the specialized Golgi complexes. The membranes later disappear and the particles form definitive crystals by rearrangement into a hexagonal close-packed pattern.     

Intracrystalline proteins and calcium oxalate crystal degradation in MDCK II cells

We assessed the effects of intracrystalline urinary proteins on the ability of Type II Madin-Darby canine kidney (MDCK-II) cells to bind and degrade calcium oxalate monohydrate (COM) crystals. Binding of [14C]-labelled inorganic crystals (iCOM), and COM crystals precipitated from centrifuged and filtered (CF) or ultrafiltered (UF) human urine was quantified by radioactive analysis. SDS-PAGE confirmed the presence of intracrystalline proteins > 10 kDa in CF crystals and their absence from UF crystals. Morphological effects were assessed qualitatively by field emission scanning electron microscopy. iCOM crystals bound rapidly and extensively and were resistant to degradation. Binding of CF crystals was weaker than UF crystals, and both had markedly less affinity than iCOM. CF and UF crystals were extensively degraded within 90 min, the effect being more pronounced with CF. These results support our hypothesis that intracrystalline proteins protect against urolithiasis by facilitating intracellular proteolytic digestion and destruction of crystals phagocytosed by urothelial cells.     

Purification, crystallization and preliminary crystallographic analysis of porcine aldose reductase

Large crystals of porcine aldose reductase have been grown from polyethylene glycol solutions. The crystals are triclinic, space-group P1, with a = 81.3 A, b = 85.9 A, c = 56.6 A, alpha = 102.3 degrees, beta = 103.3 degrees and gamma = 79.0 degrees. The crystals grow within ten days to dimensions of 0.6 mm x 0.4 mm x 0.2 mm and diffract to at least 2.5 A. There are four molecules in the unit cell related by a set of three mutually perpendicular non-crystallographic 2-fold axes.     

利用生物可降解海藻酸钙微球保护苏云金杆菌晶体与芽胞免受紫外线降解

采用基于注射挤压器的液滴形成技术制备包裹了苏云金杆菌晶体和芽胞的海藻酸钙凝胶微球.通过调节该装置的活塞重量和空气压力,获得了平均直径为20μm的微球.SDS-PAGE分析与平板菌落涂布实验表明,凝胶微球可有效减少紫外线对苏云金杆菌晶体和芽胞的损伤作用.利用小菜蛾进行的毒力生测发现,凝胶微球可有效防止紫外线引起的晶体和芽胞杀虫毒力的下降.本研究的液滴形成技术也可适用于其它微球包裹过程.     

Crystal diversity and macropatterns in leaves of Oleaceae

Oleaceae leaves surveyed from herbarium specimens of 240 species from 23 genera were rehydrated, bleached, processed into xylol, mounted unstained, and viewed microscopically between crossed polarizers. Occurrence of five crystal types and two variants (tiny acicular crystals and sphaerites) within one family is unusual. Number of crystal types within a single species was one (108 spp.), two (53 spp.), three (51 spp.), four (15 spp.), and five (6 spp.). Seven species lacked crystals. The tiny acicular crystal variant was most common (167 spp.), followed by prisms (67 spp.), raphides (65 spp.), druses (61 spp.), sphaerites variant (50 spp.), styloids (36 spp.), and crystal sand (21 spp.). Epidermal crystals were common (155 spp.), with epidermal crystals clustering at base of trichomes in 21 species. Jasminum was exceptional in having mostly druses and almost no crystals around vascular bundles. Most Oleaceae crystals are tiny, usually about 5 μm in length, except for larger styloids and raphides.