STUDIES ON THE ROOT OF HORDEUM VULGARE L.– ULTRASTRUCTURE OF THE SEMINAL ROOT WITH SPECIAL REFERENCE TO THE PHLOEM

Seminal root tissue of Hordeum vulgare L. var. Barsoy was fixed in glutaraldehyde and osmium tetroxide and studied with the light and electron microscopes. The roots consist of an epidermis, 6–7 layers of cortical cells, a uniseriate endodermis and a central vascular cylinder. Cytologically, the cortical and endodermal cells are similar except for the presence of tubular-like invaginations of the plasmalemma, especially near the plasmodesmata, in the former. The vascular cylinder consists of a uniseriate pericycle surrounding 6–9 phloem strands occurring on alternating radii with an equal number of xylem bundles. The center of the root contains a single, late maturing metaxylem vessel element. Each phloem strand consists of one protophloem sieve element, two companion cells and 1–3 metaphloem sieve elements. The protophloem element and companion cells are contiguous with the pericycle. Metaphloem sieve elements are contiguous with companion cells and are separated from tracheary elements by xylem parenchyma cells. The protoplasts of contiguous cells of the root are joined by various numbers of cytoplasmic connections. With the exception of the pore-plasmodesmata connections between sieve-tube members and parenchymatic elements, the plasmodesmata between various cell types are similar in structure. The distribution of plasmodesmata supports a symplastic pathway for organic solute unloading and transport from the phloem to the cortex. Based on the arrangement of cell types and plasmodesmatal frequencies between various cell types of the root, the major symplastic pathway from sieve elements to cortex appears to be via the companion and xylem parenchyma cells.     

HISTOLOGICAL STUDIES ON THE COLEOPTILE. II. COMPARATIVE VASCULAR ANATOMY OF COLEOPTILES OF AVENA AND TRITICUM

The vascular bundles in the uppermost 1-4 mm of the coleoptiles of 9 varieties of Avena sativa, and also of Avena fatua L., all terminate essentially vertically with a small “cap” of tracheary elements. In Triticum vulgare Vill., by contrast, they terminate with a horizontal or downward-pointing section. This brings the two bundles more or less together and may result in their complete fusion, usually with a short vascular extension. In both genera the bundles contain one or more series of apparently active, undifferentiated cells. In the mature embryos the bundles are entirely procambial in nature, but xylem differentiation begins rapidly upon germination and proceeds towards the tip, which is reached by the time the coleoptile is 1.5 mm long; thereafter it proceeds basipetally and it may continue at the base after elongation has ceased there. The differentiation of stomata also appears to proceed basipetally. It may be deduced that the coleoptile cannot form lignin while in the embryo but begins to do so upon germination. Parallels are brought out between auxin production first by the endosperm and then by the tip, on the one hand, and lignification in the xylem and in the stomata, on the other.     

THE VASCULAR SYSTEM OF THE INFLORESCENCE AXIS OF ANDROPOGON GERARDII (GRAMINEAE) AND ITS BEARING ON CONCEPTS OF MONOCOTYLEDON VASCULAR TISSUE

The vascular bundles in the inflorescence axis of Andropogon gerardii occur in inner and outer systems. The inner system is made up of large, early developing strands that, at earliest stages of development, are precocious (= the appendage they are to serve has not yet been initiated). The outer system consists of later developing smaller strands that are open ended in a proximal direction (= strands differentiate basipetally in the cortex below the appendage they serve). Bundles of both the inner and outer systems are not connected to other procambium early in their development but exist as isolated strands. The veins of the inner system of the inflorescence axis occur as sympodia. The presence of inner and outer systems in the vascular tissue is common to most monocotyledons. However, amongst monocotyledons, only certain grasses have been shown to have strands of the inner system that are isolated early in development. Many dicotyledons have large strands which are precocious and some have smaller, later developing strands which are open ended in a proximal direction, hence they occur as isolated strands. These smaller strands in dicotyledons occur between large strands. Certain dicotyledons have an inner and an outer system of veins. Of these, some have veins of the inner system that differ from the inner system bundles of monocotyledons in that they also form part of the outer system of veins, or develop at a different time. One other dicotyledon with an inner and outer system, Bougainvillea, differs from monocotyledons only in that the bundles of the outer system do not seem to be isolated early in their development and anastomoses are seen between the inner and outer systems. Thus, it appears that monocotyledons differ from dicotyledons only in the presence of independent inner and outer systems of vascular bundles in the former. Thus, the hypothesis of Zimmermann and Tomlinson that there are basic differences between monocotyledon and dicotyledon vascular systems is not substantiated. It is even suspected that monocotyledon and dicotyledon vascular systems will be demonstrated to be modifications of a basic plan consisting of large, acropetally differentiating and smaller, basipetally differentiating strands.     

Chloroplast Development in Rye Coleoptiles

In the parenchyma cells of 1-d-old dark-grown rye coleoptiles (Secale cereale) proplastids occurred which sometimes contained starch grains. During coleoptile growth in darkness starch-filled amyloplasts are formed from the preexisting proplastids. No prolamellar bodies were observed in the stroma of the plastids of the etiolated coleoptile. After irradiation of 3-d-old etiolated coleoptiles with continuous white light three different types of plastids occurred. In the epidermal cells proplastids were observed. The parenchyma cells below the stomata of the outer epidermis (above the two vascular bundles) contained mature, spindle-shaped chloroplasts with a well-developed thylakoid system. In the parenchyma cells that surround the vascular bundles amyloplasts with some thylakoid membranes (chloroamyloplasts) occurred. The mesophyll cells of the primary leaves of dark-grown seedlings contained etioplasts with large prolamellar bodies. In the primary leaves of irradiated plants chloroplasts similar to those of the parenchyma cells of the coleoptile were observed. Our results show that the rye coleoptile, which grows underground as a heterotrophic organ, is capable of developing mature chloroplasts upon reaching the light above the soil surface. The significance of this expression of photosynthetic capacity for the carbon economy of the developing seedling is discussed.     

Structural organization of the toe pads in the amphibian Philautus annandalii (Boulenger, 1906)

We describe the morphology of toe pads in the Himalayan tree frog Philautus annandalii. These are expanded tips of digits and show modifications of their ventral epidermis for adhesion. The outer cells of toe pad epidermis (TPE) bear surface microstructures (0.7 × 0.2 μm), which are keratinized. Their cytoplasm contains no organelles, but pleomorphic nuclei and mucous granules (0.4–0.5 μm) that glue the keratin filaments. In the intermediate cell layer of TPE, similar keratinized microstructures as in the outer cells are present, so that when the outer layer is shed, it is ready with features for adhesion. These cells contain more keratin than the outer cells. The basal cell layer contains thin keratin bundles and usual cell organelles. The dermis contains mucous‐secreting glands, whose ducts open in the outer epidermal cell layer in channels. The dorsal epidermal cells lack surface microstructures and keratin bundles. Ultrastructural features suggest that toe pads utilize the surface microstructures for adhesion aided by mucus, in which the intermediate cell layer seems to bear the shear stress generated during locomotion. Further, TPE can expand and fit into an increased contact area of the substrate. The long, surface microstructures may also help in mechanical interlocking with rough surfaces on plants.     

濒危植物海南风吹楠营养器官解剖结构特征

该研究采用石蜡切片和光学显微技术,对海南风吹楠营养器官的解剖结构及其对环境的适应性进行了探讨。结果表明:海南风吹楠为典型异面叶,叶片中脉发达,中部分化出髓,上表皮外侧具角质层,内侧具1层内皮层,下表皮外侧无角质层,有气孔器分布,气孔器为双环型,略下陷;栅栏组织3~4层细胞,海绵组织4~6层细胞。茎的初生结构中表皮轻微角质化,维管束为外韧型,8~10个初生维管束围绕髓排列为1轮;茎的次生结构中,表皮外部角质层加厚,维管柱紧密排列连成环状,次生韧皮部和次生木质部发达,形成层细胞3~5层。根的初生结构中表皮细胞外壁加厚,外皮层细胞体积大,形状不规则,内侧具1层形成层,内皮层具凯氏带,初生木质部为多原型,呈辐射状排列。根的次生结构中木栓层细胞5~6层,木栓层内侧具1层木栓形成层,栓内层细胞3层。海南风吹楠营养器官具有一定耐阴和耐旱结构特征,同时与其生活的热带雨林沟谷中高温荫湿的环境相适应。     

Keratinization of the outer surface of the avian scutate scale: Interrelationship of alpha and beta keratin filaments in a cornifying tissue

Summary The outer surface of adult Gallus domesticus scutate scale was studied as a model for epidermal cornification involving accumulation of both alpha and beta keratins. Electron-microscopic analysis demonstrated that the basal cells of the adult epidermis contained abundant lipid droplets and that filament bundles and desmosomes were distributed throughout the cell layers. Indirect immunofluorescence microscopy and double-labeling immunogold-electron microscopy confirmed that the stratum germinativum contained alpha keratin but not beta keratin. Beta keratins were first detected in the stratum intermedium and were always found intermingled with filament bundles of alpha keratin. As the differentiating cells moved into the outer regions of the stratum intermedium and the stratum corneum, the large mixed keratin filament bundles labeled increasingly more with beta keratin antiserum and relatively less so with alpha keratin antiserum. Sodium dodecyl sulfate-polyacrylamide gel analysis of vertical layers of the outer surface of the scutate scale confirmed that cells having reached the outermost layers of stratum corneum had preferentially lost alpha keratin. The mixed bundles of alpha and beta keratin filaments were closely associated with desmosomes in the lower stratum intermedium and with electron-dense aggregates in the cytoplasm of cells in the outer stratum intermedium. Using anti-desmosomal serum it was shown that these cytoplasmic plaques were desmosomes.     

薏苡种子胚芽鞘细胞的结构

观察了薏苡浸泡种子胚芽鞘的结构。胚芽 外,内表皮薄壁组织及２个侧位的维管束组成。在外表皮两处,观察到径向壁不边原细胞群,它们实际是合胞体。薄壁细胞含丰富的核糖体,内质网小泡和线粒体,说明代谢活动已经活跃。初生纹孔场内有胞间连丝,显示胞间已存在物质的共质运转。     

ONTOGENY OF THE PRIMARY THICKENING MERISTEM IN SEEDLINGS OF BOUGAINVILLEA SPECTABILIS

Anomalous secondary thickening occurs in the main axis of Bougainvillea spectabilis as a result of a primary thickening meristem which differentiates in pericycle. The primary thickening meristem first appears in the base of the primary root about 6 days after germination and differentiates acropetally as the root elongates. It begins differentiating from the base of the hypocotyl toward the shoot apex about 33 days after germination. The primary thickening meristem is first observable at the base of the first internode about 60 days after germination. It then becomes a cylinder in the main axis of the seedling. No stelar cambial cylinder forms in the primary root, hypocotyl, or stem because vascular cambium differentiation occurs neither in the pericycle opposite xylem points in the primary root nor in interfascicular parenchyma in the hypocotyl or stem. The primary vascular system of the stem appears anomalous because an inner and an outer ring of vascular bundles differentiate in the stele. Bundles of the inner ring anastomose in internodes, whereas those of the outer ring do not. Desmogen strands each of which is composed of phloem, xylem with both tracheids and vessels, and a desmogic cambium, differentiate from prodesmogen strands in conjunctive tissue. The parenchymatous cells surrounding desmogen strands then differentiate into elongated simple-pitted fibers and thick-walled fusiform cells that are about the same length as the primary thickening meristem initials.     

Fine structural observations on the epidermis

Summary The organization of the wall of epidermal cells in the petiole of species of Apium, Eryngium, Rumex, and Abutilon as well as that of the epidermis of Avena coleoptile has been investigated. The outer and inner tangential walls consist of layers in which the cellulose microfibrils are oriented alternately parallel or transverse to the longitudinal cell axis. This organization resembles that previously described for collenchyma cell walls (Wardrop, 1969; Chafe, 1970). On the radial (anticlinal) walls the orientation of the microfibrils is transverse and these appear continuous with the layers of transverse orientation of the outer and inner tangential walls. Variation in thickness of the outer tangential, and radial, and inner tangential walls appears to result from the variation in thickness of those layers in which the microfibrils have a longitudinal orientation. The extent to which these observations can interpreted in terms of some type of modified multi-net growth is discussed.     

SEASONAL DEVELOPMENT OF THE SECONDARY PHLOEM IN PINUS

Functional sieve cells are present at all times in the secondary phloem of Pinus banksiana Lamb., P. resinosa Ait., and P. strobus L. With regard to a given year's growth increment, all but the last-formed sieve cells (2-4 layers) cease functioning the same season they are derived from the cambium. The former overwinter and remain functional until new sieve cells differentiate in spring. Toward the end of March undifferentiated cells in the outer margin of the cambial zone begin to differentiate into sieve cells. About a week later, cambial activity (cell division) commences. All early phloem is produced by early May before new xylem differentiation begins. Most sieve cells are differentiated by late August, but a few not until late September. Cessation of function begins in late May or June with formation of definitive callose on sieve areas of the sieve cells which overwintered and continues slowly to sieve cells of the current season's early phloem. By mid-December all but the last-formed sieve cells (i.e., those which will overwinter in a functional state) are devoid of contents. Phloem differentiation precedes xylem differentiation by approximately 1 1/2 months. Xylem and phloem production cease more or less simultaneously in August, xylem and phloem differentiation in September.     

Scanning Electronmicroscopic Observations on Development and Structure of Pericarp of Nelumbo nucifera Gaertn

Pericarp of Hindu lotus is developed from the ovary wall only. It is differentiated intothe exocarp, mesocarp and endocarp which can be clearly recognized. The vascular bundles,secretory apparatus and aerenchyma are present in the ground tissue. The aeration system is.associated with stomata (St), air passages (Ap)and chamber (Ch). St apparatus with a specific form are located deeply under epidermal cells. Ap is schizogenous. Chisschizolysigenous. The wall of Ch has perforations which lead to surrounding cells. Ap and Ch arein contact with St in both outer and inner epidermis (Ep), so the aeration system covers the wholepericarp. In Ep, there are several kinds of secretory apparatus with different slimes. Lacticifers are articulated, some of them are branched and some not. In xylem, annular and helicaltracheids and vessels, in phloem, sieve tubes, companion cells and their contents can be observed. On the opposite side of the funicular attachment near stigma develops a hump. Thepericarp hump (Ph) is a specific structure in lotus. After studies on its fine structure, developing process and the relation between fruit development and Ph, the author considered thatPb functions probably as a respiratory apparatus of the developing seed.     

Fine structure of the dioptric apparatus in the stalk eye of Onchidium verruculatum (Gastropoda, Stylommatophora): a distinct lamellar substructure of the lens

 The dioptric apparatus of the stalk eye in Onchidium verruculatum, including a tentacular epidermis, a cornea, and a lens, was examined using transmission electron microscopy. The tentacular epidermis was formed by columnar epidermal cells, sensory dendrites, and glandular cells. The cornea was an anterior part of the eye vesicle and consisted of corneal cells which contained abundant glycogen particles but no dark pigment granules in their cytoplasm. An acellular, transparent, ellipsoidal lens was located in the center of the eye vesicle. The lens showed a marginal zone, an outer zone, a transitional zone, an inner zone, and a central region arranged concentrically. The outer zone was the most intense electron-dense region and was finely granular in structure. The marginal zone was also finely granular and surrounded the outer zone with many hair-like slender strands on the retinal side. Toward the center of the lens this homogeneous fine granularity gradually changed into globular or rod-like substructures, about 30 nm in diameter, and then abruptly transformed into a lamellar substructure of about 30 nm in thickness. The inner zone contained a mosaic of lamellar substructures which were arranged in a fingerprint pattern that was particularly enhanced with periodic acid methenamine silver proteinate staining. The center itself consisted of deformed lamellar substructures. The concentric arrangement of substructures inside the lens of the O. ver-ruculatum stalk eye is probably responsible for the concentration and/or refraction of light. Accepted: 5 December 1997     

THE TIME COURSE OF SIEVE TUBE AND VESSEL REGENERATION AND THEIR RELATION TO PHLOEM ANASTOMOSES IN MATURE INTERNODES OF COLEUS

Quantitative counts of regenerative sieve tubes and vessels were made in a large number of samples of mature internode #5 of C. blumei, with concomitant study of the fine details of vascular regeneration and the occurrence of the normally developing phloem anastomoses. Such anastomoses were found in many of the plants, but their average number in the small regenerating area was low (viz., 0.9 ± 0.2). With the phloem anastomoses excluded from the counts, the time course of regeneration was clear cut—no strands completed their regeneration around the wound until three days after wounding. More regenerative sieve tubes completed their differentiation under all conditions than did regenerative vessels. The number of sieve tubes and vessels regenerated by four days was closely related to the number of preexisting bundles of that type of vascular cell that had been severed by the transverse wound. The ratio of bundles severed by the wound in the phloem to those in the xylem was 2.14, and the ratio of the regenerative sieve tubes to the regenerative vessels was 2.24. For both tracheary and sieve tube cells the initial regeneration was strongly polar (mostly above the wound), as expected from earlier IAA transport data. The path of tracheary regeneration was obviously related to that of the sieve tubes on the other side of the cambium.     

江南油杉营养器官的解剖结构及其生态适应性

采用石蜡切片和光学显微技术对江南油杉(Keteleeria fortunei(Murr.)Carr.var.cyclolepis(Flous)Silba)根、茎、叶的解剖结构进行观测,研究其形态结构对环境的适应性。结果显示:江南油杉叶片为异面叶,上表皮厚11.5μm,外侧覆盖厚4.5μm的角质层,下表皮厚8.6μm,外侧覆盖厚2.4μm的角质层,有气孔器分布,栅栏组织由1~2层细胞组成,海绵组织由2~3层细胞组成,主脉为单脉,厚474.1μm。茎的初生结构中表皮细胞1~2层,外皮层细胞4~6层,内皮层细胞6~8层,其内分布有树脂道;次生结构中木栓层细胞2~3层,栓内层细胞1~2层,皮层内有树脂道和分泌腔分布,维管束紧密排列连成环状。根的初生结构中外皮层细胞3层,内皮层细胞1~2层,具凯氏带,初生木质部为四原型;次生结构中木栓层细胞3~4层,栓内层细胞2~3层。江南油杉营养器官的解剖结构表现出较大的可塑性,使之既能较好地适应阳生环境又对阴生环境具备一定的适应性,还可耐受一定的干旱和寒冷。     

Ricerche Sull'infrastruttura del Coleottile di Avena

Abstract

Researches on ultrastructure of Avena coleoptile. 3. The sieve elements. — A study on the ultrastructural organization of the mature sieve elements of Avena coleoptile has been carried out. Data suggest that functional phloem tubes are alive and remain alive until they are working. Judging on morphological basis, the metabolic activity of sieve elements should be of peculiar type and low in comparison to that of the companion cells. In fact the cytoplasm is located in a narrow parietal strand, mitochondria, Golgi apparatus and endoplasmic reticulum are present, but they appear very modified; plastids and nucleus are absent. The cytoplasm is bounded externally by a normal plasmalemma, whilst the vacuole has no visible limits: a tonoplast is, therefore not identifiable.

The strands connecting the superimposed sieve elements with one another through the sieve plate result to be made by a double membrane system very similar to the endoplasmic reticulum, which we believe to realize cytoplasmic continuity between phloem tubes.

The data reported are more favorable to the existence in the sieve tubes of an active mechanism of translocation of organic solutes than a passive mass-flow.

The collaboration of companion cells in the translocation mechanism has been discussed.     

药用植物川牛膝根中异常次生结构的发育解剖学研究

药用植物川牛膝的根内具有异常的次生结构。其异常的次生生长是由维管柱外围发生的异常形成层通过正常的活动方式完成的。后一轮异常形成层起源于前一轮异常形成层向外产生的薄壁组织细胞,位于韧皮部的外侧。每一轮异常形成层向内产生木质部,向外产生韧皮部,组成异常维管束。其中,木质部最先开始分化。异常维管束排成螺旋状,分散在结合组织中。除最外轮一些木质部束之间的结合组织是厚壁组织外,其余结合组织都是薄壁的。由于初生结构和早期的次生结构是正常的,所以,这种异常结构可能是后起的特征。     

ULTRASTRUCTURE AND DEVELOPMENT OF THE MICROSPORANGIUM OF PSEUDOTSUGA MENZIESII (MIRB.) FRANCO. I. DORMANT STAGES

The dormant (mid-November to mid-February) microsporangia of Pseudotsuga menziesii (Douglas-fir) contain pollen mother cells (PMC's) in diffuse diplotene, surrounded by 1–2 layers of tapetal cells and 3–4 layers of microsporangial wall cells. At the beginning of dormancy, PMC's are large and their walls are lysed. The cell walls contain a thick layer of loosely-arranged fibrils which are produced in large vesicles in the PMC cytoplasm and are secreted across the plasma membrane. PMC's contain several layers of rough ER. The inner tangential and the radial walls of the tapetal cells are lysed. During dormancy the PMC's form many new autophagic vacuoles, the chromatin consists of a network of fine threads comprised of medium-sized granules of uniform size and the nucleoli split. The outer tapetal wall is thick and becomes encrusted by an irregular lipid layer. The tapetal cytoplasm is similar to the PMC cytoplasm but is devoid of amyloplasts. The tapetal cytoplasm shows secretory activity at the beginning of dormancy and again near the end of dormancy. The later secretory activity results in the deposition of a spongy material, especially along the radial and inner walls of the tapetal cells. Tapetal cells contain 1–2 large nuclei which show prominent and irregular clumps of chromatin. Subcellular developmental changes occur in the dormant microsporangia of Pseudotsuga in much the same manner as has been reported for Pinus.     

THE ONTOGENY OF THE PRIMARY THICKENING MERISTEM OF ATRIPLEX HORTENSIS L. (CHENOPODIACEAE)

Seedlings of Atriplex hortensis were studied to ascertain; 1) in which organ the primary thickening meristem (PTM) first differentiates; 2) the direction of differentiation of the PTM, and 3) the pattern of differentiation of conjunctive tissue. The PTM initially differentiates in pericycle of the primary root base 11 days after emergence of the primary root. It then differentiates in the transition region of the hypocotyl, mostly in cells of pericycle between pairs of vascular bundles. In the upper hypocotyl, PTM differentiates by day 20 in the inner layer of cortical parenchyma. In the epicotyl, PTM apparently differentiates in the inner layer of cortex, by day 24. Desmogic xylem differentiates from radial files of internal conjunctive tissue cells and desmogic phloem differentiates opposite desmogic xylem strands from newly formed cells of external conjunctive tissue. No interfascicular cambium differentiates in the root, hypocotyl, or epicotyl.     

Seed coat development, anatomy and scanning electron microscopy of Harpagophytum procumbens (Devil's Claw), Pedaliaceae

Seed coat development of Harpagophytum procumbens (Devil's Claw) and the possible role of the mature seed coat in seed dormancy were studied by light microscopy (LM), transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM). Very young ovules of H. procumbens have a single thick integument consisting of densely packed thin-walled parenchyma cells that are uniform in shape and size. During later developmental stages the parenchyma cells differentiate into 4 different zones. Zone 1 is the multi-layered inner epidermis of the single integument that eventually develops into a tough impenetrable covering that tightly encloses the embryo. The inner epidermis is delineated on the inside by a few layers of collapsed remnant endosperm cell wall layers and on the outside by remnant cell wall layers of zone 2, also called the middle layer. Together with the inner epidermis these remnant cell wall layers from collapsed cells may contribute towards seed coat impermeability. Zone 2 underneath the inner epidermis consists of large thin-walled parenchyma cells. Zone 3 is the sub-epidermal layers underneath the outer epidermis referred to as a hypodermis and zone 4 is the single outer seed coat epidermal layer. Both zones 3 and 4 develop unusual secondary wall thickenings. The primary cell walls of the outer epidermis and hypodermis disintegrated during the final stages of seed maturation, leaving only a scaffold of these secondary cell wall thickenings. In the mature seed coat the outer fibrillar seed coat consists of the outer epidermis and hypodermis and separates easily to reveal the dense, smooth inner epidermis of the seed coat. Outer epidermal and hypodermal wall thickenings develop over primary pit fields and arise from the deposition of secondary cell wall material in the form of alternative electron dense and electron lucent layers. ESEM studies showed that the outer epidermal and hypodermal seed coat layers are exceptionally hygroscopic. At 100% relative humidity within the ESEM chamber, drops of water readily condense on the seed surface and react in various ways with the seed coat components, resulting in the swelling and expansion of the wall thickenings. The flexible fibrous outer seed coat epidermis and hypodermis may enhance soil seed contact and retention of water, while the inner seed coat epidermis maintains structural and perhaps chemical seed dormancy due to the possible presence of inhibitors.