P-ring: The conserved nature of phosphorus enriched cells in seedling roots of distantly related species

Plants require sunlight, carbon dioxide, water and mineral ions for their growth and development. Roots in vascular plants sequester water and ions from soil and transport them to the aboveground parts of the plant. Due to heterogeneous nature of soil, roots have evolved several regulatory barriers from molecular to organismic level that selectively allows certain ions to enter the vascular tissues for transport according to the physiological and metabolic demands of plant cell. Current literature profusely elaborates about apoplastic barriers, but the possibility of the existence of a symplastic regulation through phosphorous-enriched cells has not been mentioned. Recent investigations on native ion distribution in seedling roots of several species (Pinus pinea, Zea mays and Arachis hypogaea) identified an ionomic structure termed as "P-ring". The P-ring is composed of a group of phosphorous-rich cells arranged in radial symmetry encircling the vascular tissues. Physiological investigations indicate that the structure is relatively inert to external temperature and ion fluctuations while anatomical studies indicates that they are less likely to be apoplastic in nature. Furthermore, their localization surrounding vascular tissues and in evolutionarily distinct plant lineages might indicate their conserved nature and involvement in ion regulation. Undoubtedly, this is an interesting and important observation that has significant merit for further investigations by the plant science community.

Endogenous nutrients are concentrated in specific tissues in the Zea mays seedling

K, P, Cl, and Ca are distributed in tissue-specific patterns in Zea mays seedlings. These elements were mapped and analyzed using a relatively simple semi-quantitative technique, i.e., fast freezing, followed by freeze fracturing, then freeze drying, and finally scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS). In the radicle, endogenously derived (i.e., from seed) K and P transition from being homogenous in the apical meristem to tissue-specific in older regions. At 3 mm from the radicle apex, K concentration is approximately 40 mM in mid-cortex and decreases by approximately 50% at 15 mm. From 3 to 55 mm, P concentration in pericycle is approximately twice that found in adjacent regions. Ca is not detectable in younger portions of the radicle by SEM/EDS, but in older regions, it is present at 13 mM in mid-cortex. K concentration values of entire radicles analyzed with inductively coupled plasma optical emission spectrometry (ICP-OES) exceeded the SEM/EDS values. For Ca, the reverse was true. But, SEM/EDS analysis did not include several vascular tissues that contained high concentrations of K and low concentrations of Ca. The inception of lateral root primordia was accompanied by a localized decrease in Ca in cortical regions that were centrifugal to the primordium tip. A region of O-rich cells in endosperm was identified centripetal to the aleurone. These results indicate that (1) outer, mid-, and inner cortical regions, as well as the adjacent tissues, have distinct ion accumulation properties, and (2) ions are concentrated in some radicle tissues prior to development of Casparian strips.

Tissue accumulation patterns and concentrations of potassium, phosphorus, and carboxyfluorescein translocated from pine seed to the root

Potassium (K), phosphorous (P), and carboxyfluorescein (CF) accumulate in functionally distinct tissues within the pine seedling root cortex. Seedlings of Pinus pinea translocate exogenous CF and endogenous K and P from the female gametophyte/cotyledons to the growing radicle. Following unloading in the root tip, these materials accumulate in characteristic spatial patterns. Transverse sections of root tips show high levels of P in a circular ring of several layers of inner cortical cells. K and CF are minimal in the high P tissue. In contrast, high levels of K and CF accumulate in outer cortical cells, and in the vascular cylinder. These patterns are a property of living tissue because they change after freeze-thaw treatment, which kills the cells and results in uniform distribution of K and P. K concentration can be reduced to undetectable levels by incubation of roots in 100 mM NaCl. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis and scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS) of root segments both reliably determine K and P concentrations.

F-actin distribution in root primary tissues of several seed plant species

PREMISE OF THE STUDY

Primary vascular tissues of angiosperm and gymnosperm roots have significant anatomical differences. In gymnosperms, lack of protophloem sieve elements indicates a lengthy parenchymatous pathway for nutrient transport to the root apical meristem (RAM). Because F-actin is an essential component of transport in parenchyma cells, the distribution of F-actin was determined and compared among roots of several angiosperm and gymnosperm species.

METHODS

Roots were chemically fixed and sectioned by hand to enable rapid production of many sections for labeling F-actin with phalloidin.

KEY RESULTS

In angiosperm and gymnosperm root tips, relative intensity of F-actin labeling was highest in primary vascular tissues. Parenchyma cells in and around protophloem tended to have more F-actin while cells in cortical and protoxylem tissues tended to have less. In gymnosperms, phloem parenchyma was intensely labeled for several millimeters distal to the root apical meristem (RAM), and the F-actin is mostly composed of bundles that lie parallel to the root longitudinal axis. This orientation differed from the multidirectional arrangement of F-actin filaments in cortical cells. In angiosperms, intense F-actin labeling of pericycle and phloem parenchyma cells occurred around the first mature sieve elements.

CONCLUSIONS

F-actin is concentrated in the vascular cylinder, commonly in primary phloem parenchyma. In gymnosperms, the absence of sieve elements suggests that cytoplasmic streaming has a role in some aspect of phloem transport or unloading. In angiosperms, the region of intense F-actin labeling in the phloem parenchyma is limited to the extreme terminal portion of primary phloem where unloading of the earliest mature sieve elements occurs.

Interplay between protein-modified surface and functional response of osteoblasts

The objective of the study is to elucidate the interplay between fibronectin-metal hybrid surfaces and osteoblast function. The practical relevance is that a significant initial step in the process of prosthetic integration within a physiological system is the rapid adsorption of proteins, including fibronectin, on the surface of biomedical device. Here, we compare and contrast the cell-substrate interactions on bare and protein-modified surfaces. The protein adsorption on the surface was beneficial in favorably modulating biological functions including cell attachment, proliferation, and viability. Additionally, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on protein-adsorbed surfaces. These results support the hypothesis that protein adsorption on artificial biomedical devices can promote bioactivity and regulate biological functions.

Interplay between grain structure and protein adsorption on functional response of osteoblasts: ultrafine-grained versus coarse-grained substrates

The rapid adsorption of proteins is the starting and primary biological response that occurs when a biomedical device is implanted in the physiological system. The biological response, however, depends on the surface characteristics of the device. Considering the significant interest in nano-/ultrafine surfaces and nanostructured coatings, we describe here, the interplay between grain structure and protein adsorption (bovine serum albumin: BSA) on osteoblasts functions by comparing nanograined/ultrafine-grained (NG/UFG) and coarse-grained (CG: grain size in the micrometer range) substrates by investigating cell-substrate interactions. The protein adsorption on NG/UFG surface was beneficial in favorably modulating biological functions including cell attachment, proliferation, and viability, whereas the effect was less pronounced on protein adsorbed CG surface. Additionally, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on protein adsorbed NG/UFG surface. The functional response followed the sequence: NG/UFG(BSA) > NG/UFG > CG(BSA) > CG. The differences in the cellular response on bare and protein adsorbed NG/UFG and CG surfaces are attributed to cumulative contribution of grain structure and degree of hydrophilicity. The study underscores the potential advantages of protein adsorption on artificial biomedical devices to enhance the bioactivity and regulate biological functions.

Effects of copper on osmoregulation in sheepshead minnow, Cyprinodon variegatus acclimated to different salinities

The sheepshead minnow, Cyprinodon variegatus is a euryhaline fish that inhabits estuaries and coastal marshes where it encounters a wide range of salinities. Many of these areas also have elevated levels of contaminants, creating the potential for toxic ions to interfere with the uptake of ions for osmoregulation. To determine whether the effect of copper on osmoregulatory activity is dependent on the osmotic conditions that individuals have been living at, fish were acclimated for 14 days to 2.5, 10.5 or 18.5 ppt seawater and then exposed to a fixed free cupric ion level (14.6 μM Cu2+) for 6 h. Plasma Na, plasma Cl, wet/dry weight ratio, transepithelial potential difference (TEPD) and branchial Na(+)/K(+)-ATPase activity were determined before and after copper exposure. We also computed Na and Cl equilibrium potentials. Following the salinity acclimation (in fish not yet exposed to copper), fish from the low salinity group (2.5 ppt) had lower TEPD, lower plasma Na levels and higher branchial Na(+)/K(+)-ATPase activity compared to the fish acclimated to higher salinities. No differences in plasma Cl and wet/dry weight ratio were detected. Copper exposure caused a significant decrease in plasma Na levels and Na(+)/K(+)-ATPase activity and an increase in wet/dry weight ratio, but these changes were limited to the 2.5 ppt salinity group. No significant changes in plasma Cl were detected. Copper treatment resulted in a small decrease in TEPD for all except the lowest salinity acclimation group. A comparison of equilibrium potentials with TEPD showed evidence of active transport of both Na and Cl in 2.5 ppt acclimated fish but not for the 10.5 or the 18.5 ppt acclimated fish. Our results show that effects of copper on osmoregulation are dependent on the fish' past salinity regime, and that these effects tend to be more pronounced for euryhaline fish that have been living under hyposmotic conditions.

F-actin in conifer roots

The distribution of F-actin in the complex tissues of a higher plant organ has been visualized by fluorescence labeling the roots of the conifers Chamaecyparis obtusa and Pseudotsuga menziesii with F-actin-specific fluorescent dye-conjugated phallicidin. F-actin is present in the parenchymatous cells of the vascular tissue. Some vascular parenchyma cells possess larger numbers of F-actin-containing structures (microfilament bundles) than are known to exist in any other higher plant cell. Tissue type appears to be an important determinant of the presence or absence of F-actin in a cell. For example, in contrast to vascular cells, cortical cells show no indication of fluorescence labeling of F-actin after incubation with fluorescent phallicidin. Cytoplasmic streaming is seen only in vascular cells and in a pattern that reflects the intracellular distribution of F-actin.

Cotton-fiber germin-like protein. II: Immunolocalization, purification, and functional analysis

Cotton (Gossypium hirsutum L.) contains a germin-like protein (GLP), GhGLP1, that shows tissue-specific accumulation in fiber. The fiber GLP is an oligomeric, glycosylated protein with a subunit size of approximately 25.5 kDa. Accumulation of GhGLP1 occurs during the period of fiber elongation [4-14 days post-anthesis (DPA)]. During early phases of fiber development (2-4 DPA), GhGLP1 localizes to cytoplasmic vesicles as shown by confocal immunofluorescent microscopy. In slightly older fibers (7-10 DPA), GhGLP1 localizes to the apoplast. In other plants, germins and GLPs have been reported to have enzymatic activities including oxalate oxidase (OxO), superoxide dismutase, and ADP-glucose pyrophosphatase. Cotton fiber extracts did not contain OxO activity, nor did intact fibers stain for OxO activity. A four-step purification protocol involving ammonium sulfate precipitation of a 1.0 M NaCl extract, ion-exchange chromatography on DEAE-Trisacryl M, lectin-affinity chromatography, and gel filtration chromatography resulted in electrophoretically pure GhGLP1. While 1.0 M NaCl extracts from 10-14 DPA fiber contained superoxide dismutase and phosphodiesterase activities, GhGLP1 could be separated from both enzyme activities by the purification protocol. Although a GLP accumulates in the cotton fiber apoplast during cell elongation, the function of this protein in fiber growth and development remains unknown.

A subclass of myosin XI is associated with mitochondria, plastids, and the molecular chaperone subunit TCP-1? in maize

The role and regulation of specific plant myosins in cyclosis is not well understood. In the present report, an affinity-purified antibody generated against a conserved tail region of some class XI plant myosin isoforms was used for biochemical and immunofluorescence studies of Zea mays. Myosin XI co-localized with plastids and mitochondria but not with nuclei, the Golgi apparatus, endoplasmic reticulum, or peroxisomes. This suggests that myosin XI is involved in the motility of specific organelles. Myosin XI was more than 50% co-localized with tailless complex polypeptide-1alpha (TCP-1alpha) in tissue sections of mature tissues located more than 1.0 mm from the apex, and the two proteins co-eluted from gel filtration and ion exchange columns. On Western blots, TCP-1alpha isoforms showed a developmental shift from the youngest 5.0 mm of the root to more mature regions that were more than 10.0 mm from the apex. This developmental shift coincided with a higher percentage of myosin XI /TCP-1alpha co-localization, and faster degradation of myosin XI by serine protease. Our results suggest that class XI plant myosin requires TCP-1alpha for regulating folding or providing protection against denaturation.

Biochemical analysis of elastic and rigid cuticles of Cirsium horridulum

The cuticle is a complex structure of soluble lipids, lipid polymers and polysaccharides. In addition to its functions to reduce water loss and provide a protective barrier, its mechanical properties may be significant to plant growth and development. We investigated the cuticle of Cirsium horridulum Michx. because of its involvement in the thigmonastic contraction of staminal filaments. The staminal filaments and portions of the style are surrounded by a highly elastic cuticle in contrast to the rigid cuticle of the corolla and leaves. Our aim was to determine if the biochemical composition affected the elasticity of the cuticle. We discovered that the ratio of carbohydrates to lipids is 1:7 in floral parts but 2:1 in leaf cuticle. Esterified cutin components represented about 80% of the cuticle and di-hydroxyhexadecanoic acids were the major monomers of cutin, regardless of origin. The cutin of elastic tissues is characterized by a higher content of tri-hydroxy monomers than the cutin of rigid tissues. The data suggest that hydroxyl groups enhance the hydrophilic character of the cuticle and contribute to cuticular elasticity.

Maize myosins: diversity, localization, and function

This first analysis of monocotyledon myosin genes showed that at least five genes, one of which was probably spliced to yield two isoforms, were expressed in maize (Zea mays L.). The complete coding sequence of ZMM1 was determined, as were most of the sequences of two other myosin cDNAs (ZMM2 and ZMM3). ZMM1 and ZMM2 belonged to myosin class XI while ZMM3 was in class VIII. ZMM1 was abundantly expressed in leaves, roots, coleoptiles, and stems. ZMM3 showed a similar distribution but was expressed poorly in pollen. ZMM2 was predominantly expressed in seeds and may be part of a suite of cytoskeletal proteins in reproductive tissues. Phylogenetic analysis suggested that the origin of myosin classes VIII and XI predated that of angiosperms. Immunofluorescence studies using M11L1, a myosin XI antibody specific for the exposed loop 1 head region of myosin, indicated that myosin XI occurred in the cytoplasm of all root tip cells. The highest concentration of myosin XI was in the differentiating epidermal cells. In dividing cells, myosin XI was present near the cytokinetic apparatus at approximately the same concentration seen in other portions of the cytoplasm. Western blot analysis of subcellular fractions indicated that myosin XI was concentrated in mitochondria and low-density membranes.

The internal cuticle of Cirsium horridulum (Asteraceae) leaves

Leaf internal cuticle has not previously been studied in detail, and yet its existence has profound implications for the path of water movement. The internal cuticle forms a uniform layer on the inner periclinal epidermal walls that border substomatal cavities. This cuticle is continuous with the external cuticle through the stomatal pores. The thickness of the internal cuticle on nonstomatal epidermal cells is approximately one-third that of the external cuticle on the same cells. On both the abaxial and adaxial sides of the leaf the internal cuticle forms irregularly shaped islands bordered by mesophyll cells. The size of the islands coincides with the epidermal area of the substomatal cavity. The internal cuticle remains intact and connected to the external cuticle after incubation in cellulytic enzymes. After treatment with sulfuric acid or chloroform, both cuticles remain intact. The autofluorescence of both cuticles is increased by staining with auramine O. These results indicate that large portions of the leaf epidermis are covered by both an internal and an external cuticle.

Dynamic changes in the distribution of cytoplasmic myosin during Drosophila embryogenesis

Dramatic changes in the localization of conventional non-muscle myosin characterize early embryogenesis in Drosophila melanogaster. During cellularization, myosin is concentrated around the furrow canals that form the leading margin of the plasma membrane as it plunges inward to package each somatic nucleus into a columnar epithelial cell. During gastrulation, there is specific anti-myosin staining at the apical ends of those cells that change shape in regions of invagination. Both of these localizations appear to result from a redistribution of a cortical store of maternal myosin. In the preblastoderm embryo, myosin is localized to the egg cortex, sub-cortical arrays of inclusions, and, diffusely, the yolk-free periplasm. At the syncytial blastoderm stage, myosin is found within cytoskeletal caps associated with the somatic nuclei at the embryonic surface. Following the final syncytial division, these myosin caps give rise to the myosin rings observed during cellularization. These distributions are observed with both whole immune serum and affinity-purified antibodies directed against Drosophila non-muscle myosin heavy chain. They are not detected in embryos stained with anti-Drosophila muscle myosin antiserum or with preimmune serum. Although immunolocalization can only suggest possible function, these myosin localizations and the coincident changes in cell morphology are consistent with a key role for non-muscle myosin in powering cellularization and gastrulation during embryogenesis.

Contractile proteins in Drosophila development

In summary, we have used a multidisciplinary approach to the analysis of actomyosin-based motility during Drosophila embryogenesis. We have documented the movements of early embryogenesis with modern, video methods. We have characterized the cytoplasmic myosin polypeptide, made specific polyclonal antisera to the molecule, studied its distribution during early embryogenesis, cloned and partially characterized the gene that encodes it, and have recently completed the nucleotide sequence of a nearly full length cDNA that encodes the entire protein-coding region. We have initiated studies on myosin function in living embryos both by direct microinjection of antibodies and through classical genetics. To better understand how myosin function is regulated, we have begun analysis of its light chains. Finally, to investigate the molecular mechanism by which its function is integrated into a labile cytoskeleton, whose architecture is constantly changing, we have also investigated Drosophila spectrins. Together, these studies are designed to shed light on the dynamics of biologic form at the cellular level, with current focus on such complex processes as cytokinesis and morphogenesis.

Drosophila spectrin: the membrane skeleton during embryogenesis

The distribution of alpha-spectrin in Drosophila embryos was determined by immunofluorescence using affinity-purified polyclonal or monoclonal antibodies. During early development, spectrin is concentrated near the inner surface of the plasma membrane, in cytoplasmic islands around the syncytial nuclei, and, at lower concentrations, throughout the remainder of the cytoplasm of preblastoderm embryos. As embryogenesis proceeds, the distribution of spectrin shifts with the migrating nuclei toward the embryo surface so that, by nuclear cycle 9, a larger proportion of the spectrin is concentrated near the plasma membrane. During nuclear cycles 9 and 10, as the nuclei reach the cell surface, the plasma membrane-associated spectrin becomes concentrated into caps above the somatic nuclei. Concurrent with the mitotic events of the syncytial blastoderm period, the spectrin caps elongate at interphase and prophase, and divide as metaphase and anaphase progress. During cellularization, the regions of spectrin concentration appear to shift: spectrin increases near the growing furrow canal and concomitantly increases at the embryo surface. In the final phase of furrow growth, the shift in spectrin concentration is reversed: spectrin decreases near the furrow canal and concomitantly increases at the embryo surface. In gastrulae, spectrin accumulates near the embryo surface, especially at the forming amnioproctodeal invagination and cephalic furrow. During the germband elongation stage, the total amount of spectrin in the embryo increases significantly and becomes uniformly distributed at the plasma membrane of almost all cell types. The highest levels of spectrin are in the respiratory tract cells; the lowest levels are in parts of the forming gut. The spatial and temporal changes in spectrin localization suggest that this protein plays a role in stabilizing rather than initiating changes in structural organization in the embryo.

Spectrophotometric and cytochemical analyses of phosphatase activity in Beta vulgaris L

Spectrophotometric and cytochemical methods were used to investigate the localization and/or the sensitivity of phosphatase activities in aldehyde-fixed beet leaves and membrane fractions. The nonspecific acid phosphatase substrates, p-nitrophenyl phosphate and beta-glycerol phosphate, each exhibited unique spectrophotometric patterns of hydrolysis as a function of pH. Additionally, beta-glycerol phosphatase activity was primarily present on the tonoplast, whereas p-nitrophenyl phosphatase was present on the plasma membrane. Because of the unique pH response of each enzyme and their different localization, we conclude that they cannot be entirely "nonspecific." The spectrophotometric pattern of ATP hydrolysis differed from that of p-nitrophenol phosphate in that it decreased at pH 5.0-5.5 and was greatly inhibited by 10 mM sodium fluoride; however, both activities were on the plasma membrane. Therefore, we conclude that these activities represent either two enzymes or only one enzyme that differs in its ability to hydrolyze these two substrates. Generally, enzymatically produced lead deposits on the plasma membrane of non-vascular cells were as frequent and large as those on phloem cells; frequently, deposits on sieve element plasma membranes were relatively small. We therefore conclude that there is no evidence for the presence of relatively intense ATPase activity on the plasma membrane of phloem cells in beet leaf, in contrast to other species. Studies with membrane fractions indicated that formaldehyde could completely inhibit the inhibitor-sensitive phosphatase activities in mitochondrial and vacuolar fractions while preserving significant activity in the plasma membrane fraction.

Plasma membrane coat and a coated vesicle-associated reticulum of membranes: their structure and possible interrelationship in Chara corallina

Primary fixation with buffered glutaraldehyde plus 2.0 mM CaCl2 and 0.1% tannic acid results in the preservation of certain portions of the plasma membrane coat of Chara when seen with the electron microscope. Such a coat is not observable after fixation with glutaraldehyde alone. The coat appears to be present on all the above ground, vegetative cells of the male plant. Within complex invaginations of the plasma membrane, which are known as charasomes, the coat has two structural components, a central core that is either tubular or solid and a fibrous or granular peripheral region that surrounds the core. The coat material appears to be at least partially derived, via exocytosis, from the contents of single membrane-bound organelles known as glycosomes. Glycosomes seem to originate from within an assemblage of membranes and coated vesicles that can be described, in purely structural terms, as a partially coated reticulum. Such a reticulum is distinguishable from Golgi stacks because the reticulum (a) is not composed of stacked membranes, (b) is extensively involved with large, clearly detailed coated vesicles and coated invaginations, (c) is closely associated with glycosomes, and (d) is only slightly stained by the zinc-iodide-osmium tetraoxide reagent.