Vegetative anatomy of subtribe Orchidinae (Orchidaceae)

Leaves in Orchidinae are essentially glabrous; anticlinal walls of foliar epidermal cells arc basically straight-sided to curvilinear, and cells arc fundamentally polygonal on both surfaces; adaxial cells are larger than abaxial cells. Stomata arc anomocytic and usually only abaxial and superficial; substomatal chambers are small to moderate; outer and inner guard cell ledges are mostly small. There is no hypodermis nor are there fibre bundles. Mesophyll is homogeneous, chlorcnchyma cells arc thin-walled, and intercellular spaces numerous. Crystalliferous idioblasts abound. Vascular bundles are collateral, organized in a single series. and lack associated sclerenchyma. Bundle sheath cells are thin-walled and chlorophyllous. Stems are glabrous; stomata arc frequent in one species, lacking in others. Cortical cells are oval to circular, thick-walled, and interspersed with triangular intercellular spaces. Ground-tissue cells are circular, and triangular intercellular spaces are present. Vascular bundles arc collateral and scattered throughout the ground-tissue or are absent from the central ground-tissue. Epidermis in absorbing roots is one-layered and non-velamcntous. Exodcrmal cells are thin-walled and dead cell walls bear tenuous scalariform bars; some species lack an exodermis. Outer cortical cells are polygonal and lack intercellular spaces; middle layer cortical cells are rounded with triangular intercellular spaces; inner layer cells are polygonal and lack intercellular spaces. Endodermis and pericycle are thin-walled and one-layered. Vascular cylinder is mostly 7–9-arch with xylcm and phloem components alternating regularly; vascular tissue is embedded in parenchyma; pith cells are parenchymatous, polygonal, thin-walled and lack intercellular spaces. Root tubers generally bear a velamen of variable thickness; bulbous-based unicellular hairs frequently form a dense mat; exodermal cells are thin-walled; dead cells have scalariform bars, passage cells are sparse. Ground-tissue consists of rounded water-storage and assimilatory cells interspersed with triangular or quadrangular intercellular spaces; peripheral cells arc polygonal lacking intercellular spaces. Vascular tissue consists of monarch to pentarch meristeles distributed thoughout the ground-tissue each surrounded by a uniscriale endodermis of thin-walled cells. Thin roots ofPlalanthera exhibit a typical central cylinder surrounded by a homogeneous cortex uninterrupted by meristeles; thicker roots show a central vascular cylinder and cortex in which meristeles are also present; in globoid root tubers there is no central cylinder, and the ground-tissue is replete with scattered meristeles. Because the central vascular cylinder in Platanthera gives rise to branches (meristeles), these represent components of a single vascular system and are not separate stelar entities as implied by the use of the term ‘polystele’.     

Enamel ultrastructure and masticatory function in molars of the American opossum, Didelphis virginiana

Maxillary and mandibular molars of the American opossum, Didelphis virginiana L., were viewed in the scanning electron microscope (SEM) after acid-etching or after cutting and acid-etching. Observations were made on enamel prism patterns as they relate to functional properties of the tooth at a particular site. Molars at different stages of wear were also observed under a dissecting microscope; worn surfaces were correlated with function and enamel ultrastructure. Pounding surfaces of molar cusps wear more rapidly than near-vertical shearing surfaces or crushing basins (i.e. the trigon and talonid basin). Pounding surfaces are subjected to abrasion by food and arc not normally involved in tooth-tooth contact. Near-vertical shearing surfaces and basins used for crushing do experience tooth-tooth contact, but are surprisingly more resistant to wear. Prisms at pounding sites approach the occlusal surface at a near 90° angle and are surrounded with very thick interprismatic (IP) enamel parallel to the occlusal surface of the tooth. The pounding pattern is present at tips of cusps and at occlusal surfaces of ridges of the tooth. At near-vertical shearing surfaces, the prisms approach the outer surface obliquely and are surrounded with IP crystals which are perpendicular to the vertical surface. The angle between prismatic and IP enamel in these patterns is 60–90° in a cervical to occlusal direction. In basins of the tooth used principally for crushing and some shearing, IP enamel is perpendicular to the changing slope of the basin and the prisms are usually at a 55–65° angle to the IP enamel. When the pounding and shearing-crushing patterns meet at a ridge, a distinct seam is observed. Pounding forces occur parallel to the long axis of the prisms and perpendicular to the thick IP enamel (i.e. perpendicular to the long axis of the IP crystals) lying on either side of the prisms. Shearing and crushing forces occur at an oblique angle to the prism, and interprismatic enamel is more evenly distributed about the prism. A spiral pattern is found at the bottoms of the trigon and talonid basins, but not at the bottom of the trigonid which is a non-occluding basin. It is concluded that the differential rates of wear of the enamel surfaces are necessary in maintaining the sharp cutting edges and effective crushing basins of the tribosphenic molar, and the ultrastructural arrangements of the enamel prisms are of functional significance.     

The protective effect of vitamin D against carbon tetrachloride damage to the rat liver

We investigated the protective effect of vitamin D against liver damage caused by carbon tetrachloride (CCl₄). Twenty-four male rats were divided into four equal groups: G1, untreated controls; G2, administered CCl₄; G3, administered both CCl₄ and vitamin D for 10 weeks; G4, administered CCl₄ for 10 weeks and vitamin D for 12 weeks. At the end of experiment, intracardiac blood samples were taken and liver samples were removed. Hepatic damage due to CCl₄ was assessed using biochemistry and histopathology. Glutathione (GSH) levels decreased, while malondialdehyde (MDA) levels increased in liver tissues of G2. Alanine transaminase (ALT), alkaline phosphatase (ALP), and gamma-glutamyl-transaminase (GGT) levels increased, while albumin (ALB) levels decreased. Hepatocyte degeneration, lobular disorder, sinusoid dilation, focal necrotic areas, hyperemia, and glycogen loss were observed. Hepatic fibrosis was observed around portal areas and central veins. Bridging fibrous septa were formed between portal veins. By immunohistochemistry, both matrix metalloproteinase-9 (MMP-9) and desmin reactivity were increased. All aspects of liver damage were at least partially prevented in rats treated with vitamin D. Vitamin D appears to act as an antioxidant and anti-fibrotic to protect the rat liver against damage.