Water Stress-induced Ultrastructural Changes of Leaf tissues and Cells in the Ice Plant, Mesembryanthemum crystallinum L.

A facultative halophyte ice plant, Mesembryanthemum crystallinum L., switchs over from C_3 photosynthesis to Crassulacean acid metabolism (CAM) under environmental stress, such as water stress (osmotic stress or ionic stress). The ultrastructural changes of tissues and cells during the metabolic switch were examined in common ice plants cultured hydroponically with 400 mM NaCl. To define the stress-induced metabolic switch, the concentration of malate was measured in well expanded green leaves kept in the light and dark. The concentration was significantly higher in leaves kept in the dark than in the light, indicating CAM induction by water stress in the ice plant. The leaves of stress-induced CAM plants and unstressed plants were fixed chemically by conventional methods, and ultrathin sections were examined with a light microscope and an electron microscope. In contrast with those found in unstressed plants, in stress-induced CAM plants, epidermal bladder cells were well developed, mesophyll cells changed to small and round in shape, and the intercellular spaces became remarkably narrow. These changes may be caused directly by waterstress. Furthermore, in mesophyll cells, the chloroplasts contained conspicuously swelled thylakoids and a few small starch grains. These structural changes in chloroplasts may reflect the metabolic switch induced by water stress

Structural Analysis of Dyadic Contacts in the Longitudinal Body Wall Muscle of a Mollusc Dolabella auricularia

The ultrastructure of dyads in the longitudinal body wall muscle (LBWM) of a mollusc Dolabella auricularia was studied to elucidate electro-mechano coupling in the dyadic contacts of somatic smooth muscles, and to make clear the morphological homology with the triadic contacts of skeletal muscles. In LBWM fibers, the sarcoplasmic reticulum (SR) in vesicular forms was mostly located underneath the plasma membrane, and constructed dyads, not only along the fiber surface but also around the tubular invaginations (Sugi and Suzuki, 1978)^ which resemble the transverse tubule of skeletal muscles in shape. In the junctional gap of dyads, electron-dense foot-like structures were arrayed at regular intervals. In dyads found along the fiber surface, the diameter of the foot-like structures was 18.3nm, the center-to-center distance was 30.5nm, and the junctional gap was 9.7nm. While, in triads found around the tubular invaginations, those dimensions were 18.6nm, 30.4nm and 9.6nm, respectively. No significant difference was found between the respective dimensions of the two types of dyads, indicating that they are fundamentally the same in construction. On the other hand, the measured dimensions of dyadic contacts coincided well with those of the triadic contacts of skeletal muscles. Furthermore, as found in skeletal muscle triads, a two-dimensional orthogonal array of foot-like structures on the SR junctional membrane was also confirmed by observing serial sections 35nm thick. These results indicate that the foot-like structures are truly feet, and the dyadic contacts of LBWM fibers are homologous in structure and possibly in function with the triadic contacts of skeletal muscles. This view was further supported by these experiments, proving the existence of calsequestrin in SR demonstrated by immunoelectron microscopy and the high quantity (3.02%) of fractional SR volume per fiber volume measured by the montage method

Polyoxometalates and Microporous Transition Metal Carboxylates: Synthesis, Characterization, and Oxidation Catalysis

The oxidation of alkenes and alcohols with hydrogen peroxide (H_2O_2) and molecular oxygen, is quite an interesting objective for both academic and industrial fields. In this paper, we focused on polyoxometalates and microporous transition metal carboxylates as oxidation catalysts. For H_2O_2-based epoxidation reactions catalyzed by dimeric mono, di, and trititanium (IV)-substituted Keggin polyoxotungstates, trititanium (IV)-substituted Keggin polyoxotungstate was the most active because it exhibited the fastest formation rate of active hydroperoxotitanium (IV) intermediate. Furthermore, we investigated a novel method for the grafting reaction of transition metal-substituted polyoxometalates onto a silica surface. Keggin-type vanadium(V)-substituted polyoxomolybdate (PMoV) was electrostatically anchored to a modified silica surface having cationic ammonium moiety. The PMoV-grafted silica material exhibited activities higher than those of homogeneous PMoV reactions for the oxidation of various alcohols with 1 atm dioxygen in the presence of isobutyraldehyde (IBA). Microporous copper(II) carboxylates showed unique activities for the oxidation of alcohols with H_2O_2 in a heterogeneous system, in which a green-colored species, H_2[Cu_2^(OOCC_6H_10COO)_2(O_2)]・H_2O was one of the active oxidizing intermediates

Benzothiazolylphenol–Substituted Ketoester is a Useful Fluorescent Probe for Detection of the Mitochondrion in Sea Urchin Sperm

One of the ketoesters derived from benzothiazolylphenol-substituted dioxetane,benzothiazolylphenol-substituted ketoester (TPKE), demonstrates fluorescence in a 0.1 MNaOH 1). In this study, the fluorescent staining of a living cell with TPKE was demonstratedby fluorescence microscopy. When sperm from two species of sea urchins—Pseudocentrotusdepressus and Anthocidaris crassispina—were used as biological materials, TPKE showed afluorescent signal in the midpiece that was composed of a single mitochondrion. The ratioof fluorescent signal intensity to background noise (S/N) was high in the sperm stained with1.0–5.0 μg/ml TPKE in normal artificial seawater (pH 8.0). The S/N ratio decreased inacidic seawater (pH 6.0); acidic conditions repress respiratory activity in sea urchin sperm.Moreover, in the presence of the respiratory chain inhibitor antimycin A and the uncouplercarbonyl cyanide p--trifluoromethoxyphenyl-hydrazone, the sperm showed faint or nofluorescence in normal artificial seawater (pH 8.0). Sea urchin sperm stained with TPKEafter fixation showed faint or no fluorescence. These results suggest that TPKE is apotential fluorescent probe of living sea urchin sperm mitochondria with high respiratoryactivities

X-ray Microanalysis Studies on the Calcium Localization along the Inner Surface of Plasma Membranes in the Anterior Byssus Retractor Muscle of Mytilus edulis

To investigate the role of plasma membranes in the regulation of intracellular Ca translocation in smooth muscles, the intracellular Ca localization in the anterior byssus retractor muscle (ABRM) of Mytilus edulis was examined by the quantitative X-ray microanalysis of cryosections. When the spot analysis was carried out successively along the plasma membrane in the cryosections of resting ABRM fibers, significant amounts of Ca (～8 mmol/kg dry wt) were frequently detected, although in some cases the Ca concentration was negative. Averaged Ca concentration detected was approximately 3.0 mmol/kg dry wt (n=25), while the Ca concentration was negligible at the myoplasm. By the pyroantimonate method including the semi-quantitative X-ray microanalysis, the intracellular Ca localization and its translocation during the contraction were also observed. These results indicate that, in the ABRM fibers, the plasma membranes accumulate Ca on their inner surface, and release Ca to cause contraction

Pigment Changes and Ultrastructural Morphogenesis of Chromoplasts during Fruit Ripening of Pimentos

The correlative change of pigments with chromoplast morphogenesis in the pericarpof yellow and red pimentos during fruit ripening was examined by pigment spectrophotometryand electronmicrosopy. The metamorphosis of plastids, chloroplasts to chromoplasts, occurredwith the decrease of chlorophyll contents and the appearance of newly synthesized carotenoids,chloroxanthin in yellow pimentos and possibly capsanthin and/or capsorubin in red pimentos.As ripening proceeded, in plastids, plastoglobuli increased in both number and size, in contrastwith the degradation of grana-stack and the fragmentation of stromal thylakoids. The plastidsof yellow-ripe fruit pericarps contained exclusively plastoglobuli of various sizes at the center ofstroma, indicating G (globular)-type chromoplasts, while the plastids of red-ripe fruit pericarpsincluded a few enlarged plastoglobuli and electron-dense inclusions of various configurations,which possibly transformed from plastoglobuli to finally form needle-shaped carotenoidcrystalloids. They were determined as an intermediate-type between G-type and F (filament)-typechromoplasts, and it was reconfirmed that, during chromoplast maturation, needle-shapedcarotenoid crystalloids are formed by the elongation of enlarged plastoglobuli, concomitant withthe increase of cartotenoid contents

Examination of the Most Suitable Preparation Method for Pollen Observation by Scanning Electron Microscope

To examine the most suitable method to prepare pollen for scanning electronmicroscope observation, several fixation methods and dehydration (or drying) methods wereapplied to Arabidopsis and lily pollen obtained from flowers before and after flowering.Light and confocal laser microscope observations revealed that, in both plants, pollenobtained before flowering was swollen and wet, while that obtained after flowering wasshrunken and dry. For scanning electron microscopy, pollen was unfixed or fixed with 50%(eventually 100%) acetone, FAA (5% formalin with 50% ethanol and 5% acetic acid) or 6%glutaraldehyde solutions. It was then dried naturally in air or artificially by either criticalpoint-dry or freeze-dry machines, respectively. The results indicated that, for scanningelectron microscope observation of dry pollen, the most suitable treatment is natural dryingwithout fixation. On the other hand, to observe wet pollen, the combination of FAA orglutaraldehyde fixation with artificial drying using either machines is preferable, andfixation with acetone is unsuitable.テクニカルノー

Morphogenesis of Chloroplasts during the Illumination in Etiolated Cotyledons of a C4 Plant Amaranthus

To investigate the development of plastids in various leaf tissues of a NAD-MEtype C4 plant, Amaranthus patulus Bertoloni, structural changes of etioplasts undercontinuous illumination were observed by means of an electron microscope. Before theillumination, all etioplasts in epidermal cells including guard cells, mesophyll cells, bundlesheath cells, and vascular parenchymatous cells were small and spherical in shape, andcontained prolamellar bodies with extending single-thylakoids. After the illumination, theplastids elongated, and the disorganization of prolamellar bodies and the formation ofprimary grana occurred at first in epidermal plastids, secondary in mesophyll plastids,then in bundle sheath plastids, and finally in vascular parenchymatous plastids. Thisdifference of start for plastid morphogenesis among leaf tissues may be reflected simply bythose anatomical arrangement for light exposure. The function of peripheral reticulumfound in mesophyll and bundle sheath chloroplasts and the crystalline iclusion in epidermalplastids was also discussed