STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA III. PERMIAN SEEDS

Small, anatomically preserved gymnospermous seeds are detailed from late Permian age silicified specimens collected in the Beardmore Glacier region of Antarctica. The seeds are platyspermic with prominent, sarcotestal wings and a simple pollen chamber. The integument consists of a narrow endotesta, a two-parted sclerotesta and a complex sarcotesta. In mature seeds, the nucellus is present as a papery layer, separated from the endotesta by a nucellar and endotestal cuticle. Cellular megagametophytes are present in many of the seeds and commonly contain two archegonia. A multicellular embryo is present within each archegonium. The embryos are at a similar stage of development and provide evidence of simple polyembryony in these seeds. Although the affinities of the seeds are not presently known, they are discussed in the context of other seeds described from Gondwana deposits, as well as the known flora from the Beardmore Glacier area.     

Development of ovule,fruit and seed of Xyris (Xyridaceae,Poales) and taxonomic considerations

The development of the ovule, fruit and seed of Xyris spp. was studied to assess the embryological characteristics of potential taxonomic usefulness. All of the studied species have (1) orthotropous, bitegmic and tenuinucellate ovules, with a micropyle formed by both the endostoma and exostoma; (2) a cuticle in the ovules and seeds between the nucellus/endosperm and the inner integument and between the inner and outer integuments; (3) helobial, starchy endosperm; (4) a reduced, campanulate and undifferentiated embryo; (5) a seed coat formed by a tanniferous endotegmen, endotesta with thick‐walled cells and exotesta with thin‐walled cells; and (6) a micropylar operculum formed from inner and outer integuments. The pericarp is composed of a mesocarp with cells containing starch grains and an endocarp and exocarp formed by cells with U‐shaped thickened walls. The studied species differ in the embryo sac development, which can be of the Polygonum or Allium type, and in the pericarp, which can have larger cells in either endocarp or exocarp. The Allium‐type embryo sac development was observed only in Xyris spp. within Xyridaceae. Xyris also differs from the other genera of Xyridaceae by the presence of orthotropous ovules and a seed coat formed by endotegmen, endotesta and exotesta, in agreement with the division of the family into Xyridoideae and Abolbodoideae. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 619–628.     

A New Species of Petrified Ovules of Late Paleozoic

Ovules (or seeds) are distributed widely in the beds of Paleozoic of China, but what have been found are all impressions or molds of them. Recently, while studying the fossil plants in coal balls of Coal Seam No.7 (P1) at the upper part of Taiyuan Formation in Xishan Coal- Field, Taiyuan, Shanxi Province, We found a kind of petrified ovules with internal structures, which not only are abundant but also quite well presserved. Having been studied, they are put into Cardiocarpus Brongniart and considered as a new species C. samaratus. In the coal bails they are often found associated with the leaves, stems and fructifications of Cordaites, so it is very possible that these ovules belong to Cordaites. It is very interesting that these ovules are very similar to those of the earliest conifers Lebachia described by G. M. Rothwell in 1982. This indicates' that there is a close relation between Cordaites and conifers. Cardioearpus samaratus ap.nov. The ovules are small, flat and obviously-winged. The average length is 6–7mm. The largest width (nearly equal to the length) is at the lower middle part of the ovule. Wings and the top and base of the ovule bend to the same side in a varying extent. The ovule is not cordate at the base. The integument can be divided into three layers: the sarcrotesta consisting of parenchymatous cells, the sclerotesta and the endotesta consisting of longitudinally-elongated sclerenchymatous and parenchymatous cells. The lower midrile part of the nucellus is vascularized. The micropyle is elliptical in transverse section. One main vascular bundle extends upwards from the base. Before it arrives at the sclerotesta, it biforcates into two vascular bundles and extend upwards in the sarcrotesta at the wings. In the meantime, the main vascular bundle continues' to extend upwards and passes across the sclerotesta and reaches the base of the nucellus from where it extends into the nucellus.     

Seed development and function inArtabotrys hexapetalus (Annonaceae)

Until now seeds ofAnnonaceae were characterized as mesotestal only. The seed ofArtabotrys hexapetalus, however, is meso- and endotestal. An outer mechanical layer which surrounds the seed as a lignified fibrous tissue is derived from the mesotesta. A complex inner mechanical layer develops from a partially multi-layered endotesta built up by crystal-containing stone cells. The multi-layered endotesta forms a prominent seed plug in the micropylar region which is prolonged along both sides of the perichalaza as inner walls. The endotesta is one-layered on the sides of the seed and participates in rumination. In addition the endotesta may serve for deposition of end-products of metabolism. The complex growing process of the perichalaza and its surrounding tissues is described in detail. The perichalazal pad of tanniferous cells forms an U-shaped septum, in conjunction with the endotesta, dividing the seed into two chambers. During seed development it functions as transmitter of nutrients from the outer chamber filled with starch grains to the nucellus, endosperm and embryo contained in the inner one. During germination this pad probably serves for the uptake of water. — At the initial phases of germination the seed dehisces into two valves along the raphal and antiraphal side. Later on an additional parenchymatous operculum covering the seed apex disintegrates and the endotestal plug fixed by its two prolongations splits along a preformed fracture line into two parts to release the seedling. Rudiments of an aril are recognizable in young seeds only. — The data obtained fromArtabotrys hexapetalus are discussed and compared with published information on seeds in other annonaceous taxa. For systematic considerations the necessity to define the origin of the annonaceous seed plug from one or the other integument is emphasized as it may prove to be an important differential character withinAnnonaceae.     

ULTRASTRUCTURE OF THE MATURE UNGERMINATED RICE (ORYZA SATIVA) CARYOPSIS. THE CARYOPSIS COAT AND THE ALEURONE CELLS

The results of a light and electron microscopic study of the caryopsis coat and aleurone cells in ungerminated, unimbibed rice (Oryza sativa) caryopses are presented. Surrounding the rice grain is the caryopsis coat composed of the pericarp, seed coat and nucellar layers. The outermost layer, the pericarp, consists of crushed cells and is about 10 μm thick. The seed coat, interior to the pericarp, is one cell thick and has a thick cuticle. Between the seed coat cuticle and endosperm are the remains of the nucellus. The nucellus is about 2.5 μm thick and has a thick cuticle adjacent to the seed coat cuticle. Interior to the caryopsis coat is the aleurone layer of the endosperm. The aleurone completely surrounds the rice grain and is composed of two cell types—aleurone cells that surround the starchy endosperm and modified aleurone cells that surround the germ. The aleurone cells of the starchy endosperm contain many aleurone grains and lipid bodies around a centrally located nucleus. The modified aleurone cells lack aleurone grains, have fewer lipid bodies than the other aleurone cells, and contain filament bundles (fibrils). Plastids of aleurone cells exhibit a unique morphology in which the outer membranes invaginate to form tubules and vesicles within the plastid. Transfer aleurone cells are not observed in the mature rice caryopsis.     

SEEDS AND EMBRYOS OF ARAUCARIA MIRABILIS

Seeds and embryos contained within the silicified ovuliferous cone Araucaria mirabilis from the Cerro Cuadrado petrified forest are described. One wingless seed, 0.8–1.3 cm in length and 0.2–0.6 cm in width, is embedded in each ovuliferous scale. Seeds show a three-layered integument and a prominent wavy nucellus which is attached basally to the endotesta. The megagametophyte contains cellular inclusions that may represent starch grains. Ovule vascularization is complex and appears most similar to that of Araucaria bidwillii. Embryos 2 mm long and 0.25 mm wide appear to be in a telo-stage period of development. Shoot apex, cotyledons, root meristem, and calyptroperiblem are present in the embryos in which vascular tissues and secretory elements were beginning to differentiate at the time of fossilization. Embryo ontogeny is considered in light of stages encountered in extant gynmosperm taxa. The absence of the microgametophyte phase in the Cerro Cuadrado collection is discussed.     

The structure of the seed in some Western Australian species of the genus Hibbertia (Dilleniaceae)

The internal structure of the seed was studied for four Western Australian species of the genus Hibbertia (Fam.: Dilleniaceae). The principal mechanical layer of the seed coat is the endotesta. The large cells of the endotesta are heavily cutinized in potentially viable seeds of all examined species. However, results for H. hypericoides show that the cells of the endotesta are distinctly less cutinized in non-viable seeds. The tegmen consists of only one layer which is spirally thickened. Remains of the nucellus enclose the endosperm. The endosperm is rich in both starch and lipids, and the embryo is underdeveloped and minute.     

STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA. IV. TRIASSIC OVULES

Small, anatomically preserved ovules are described from specimens collected at Fremouw Peak in the central Transantarctic Mountains. The ovules occur within a silicified peat in the upper part of the Fremouw Formation, which is considered to be Early to Middle Triassic. Ovules are radially symmetrical and ovoid, with an integument that consists of a narrow endotesta and a complex sclerotesta. The bilayered nucellus has a characteristic scalloped appearance and is attached to the integument only at the base. Of 43 ovules examined, 50 to 60% contain cellular megagametophyte tissue. One specimen contains a possible archegonium with embryo. Although the ovules have not been found attached, their possible affinities are discussed in relation to the known flora from this locality and other, comparable-aged floras from Gondwana.     

PALEOZOIC SEED STUDIES: A NEW PENNSYLVANIAN PACHYTESTA FROM SOUTHERN ILLINOIS

Pachytesta stewartii, a new species found in Middle Pennsylvanian coal ball deposits in southern Illinois, is 2.5 cm long and approximately 1.5 cm in width at its greatest diameter. Commissured ribs are pronounced near the apex and progressively less distinct toward the base. The integumentary system is delimited into 3 regions: outer sarcotesta, middle sclerotesta, and thin endotesta. Conspicuous in the new species is a pronounced basal extension with an enclosed chamber that may be the result of decomposition of thin-walled parenchyma cells. Relationships with other species and possible significance of the chalazal chamber are discussed.     

Pollen movement in the micropylar canal ofLarix and its simulation

InLarix pollen captured by the ovule and rested at the distal end of the micropylar canal is transferred upward to the nucellus before it develops a pollen tube. This upward movement occurs after the canal is filled with secreted fluid, despite the fact that the pollen sinks in the fluid. We examined the mechanism of the movement based on the morphology of the canal and its simulation using pipettes. When a water column moves upward in a waxed pipette, suspended particles also move upward carried by the meniscus. InL. x eurolepis the inner surface of the integument lining the micropylar canal is coated by a cuticle layer. This layer is further coated by an integumentary membrane before the fluid is secreted. This membrane, however, becomes distorted or disappears during fluid secretion. The exposed cuticle and the degenerated hydrophilic nucellar apex may facilitate the movement of the meniscus toward the nucellus as in the simulated pipette. Pollen is interpreted to move by being carried by the meniscus when the fluid recedes.     

A structural investigation of the ovule in sugar beet, Beta vulgaris: The micropylar nucellus

At the mature stage of ovule development the micropylar part of the crassinucellate nucellus in sugar beet, Beta vulgaris has been investigated by light and electron microscopy. Compared to the main body of the nucellus the columnar cells in the micropylar part appear more meristematic and display a number of structural characteristics indicative of high metabolic activity, e.g. abundant mitochondria, dilated endoplasmic reticulum, numerous dictyosomes and coated vesicles often fusing with irregular and strongly PAS+ cell walls. This tissue undergoes a gradual degeneration after having reached the mature stage and this degeneration seems to be independent of both pollination and fertilization. The cuticle structure of the apical cells in the micropylar nucellus is very similar to cuticles of stigmatic papillae in other plants, which may be related to this tissue being predetermined to be recognized and penetrated by pollen tubes. The ultrastructural features of the micropylar nucellus cells are well in accordance with a secretory activity related to penetration and guidance of pollen tubes. It is discussed whether mitochondrial conversion of ACC to ethylene in these cells might be involved in pre- and postfertilization processes.     

Additional observations on Rhynchosperma quinnii (Medullosaceae): a permineralized ovule from the Chesterian (Upper Mississippian) Fayetteville Formation of Arkansas

New ovules from the Fayetteville Formation (Upper Mississippian) of Arkansas expand our knowledge of the morphology and anatomy of Rhynchosperma and suggest it was produced by a medullosan seed fern. Rhynchosperma has been described as radially symmetrical with a two-layered integument and vascularization in the integument only. The apical portion of the integument is ribbed; the nucellus is fused to the integument and apically differentiated into a dome-shaped pollen chamber. The vascular system is incompletely known and apparently restricted to the base of the integument. The new specimens are like Rhynchosperma in external shape, size, number of ribs, and numerous histological features. However, new data reveal that the nucellus is vascularized by a sheath of tracheids, the integument is vascularized by discrete bundles, the pollen chamber has a nucellar beak, and the nucellus is attached to the integument for a variable distance from the base. In addition, the integument is tripartite with an elaborate apical region; ribs formed by the integument are more pronounced at the apex; and internally open, hollow lobes form a stellate micropylar canal. The presence of a tripartite integument, the nature of the vascular system, the nucellus-integument attachment, the pollen chamber structure, symmetry, and the association with medullosan vegetative remains suggest medullosan affinity for these ovules and strengthens the evidence for the origin of the family before the end of the Lower Carboniferous.     

Ultrastructural studies on the microfilaria of Cardianema sp. Alicata, 1933 (Nematoda; Onchocercidae)

The ultrastructure of the sheath, cuticle and hypodermis of the microfilaria of Cardianema sp, is described from electron micrographs of in utero- and blood-stages. The trilaminiar sheath invests the microfilaria throughout development in utero and it acquires a superficial coat after the microfilaria enters the blood stream of its reptile host. The cuticle consists of external and internal cortex, fibrillar and subfibrillar layers. The cuticle is attached to the hypodermis without the intervention of a basal lamina. The structure of the external cortex is modified in the annular furrows in the cuticle. The cellular hypodermis forms a complete subcuticular layer, although over much of the circumference the cells exist as thin cytoplasmic processes and where these overlap there are extensive tight junctions. The case for classifying the microfilaria of Cardianema a first stage larva is advanced and a functional but speculative, role for the sheath is proposed.     

Ultrastructural Variation of Cuticular Layers in Cephalobinae (Nemata: Rhabditida)

The ultrastructure of the body wall cuticle in Acrobeles complexus, Cervidellus alutus, and Zeldia punctata was studied as a step toward understanding biological diversity within Cephalobinae, and to discover new characters for phylogeny-based classification of the suborder. In each species the cuticle consists of cortical, median, and basal layers. The cortical layer includes an external trilaminate and internal granular zone; the basal layer is striated. In Z. punctata the median layer is electron-lucent, vacuolar, and penetrates the cortical layer; it also includes periodically dense columns that apparently correspond to punctuations visible with light microscopy. In contrast, the median layer of the body wall cuticle in A. complexus and C. alutus is bisected by a zone that undulates parallel to the nematode surface and with periodicity corresponding to annuli. Phylogenetic analysis, using derived cuticle patterns of Cephalobinae, requires an understanding of ecological pressures that could result in convergent evolution of cuticle characters.     

An ultrastructural study of the invasion of Ascaris suum larvae by neutrophils

Neutrophils are capable of penetrating the cuticle of the second-stage larvae of the nematode Ascaris suum. The integrity of the internal tissues of the larvae is then destroyed by cytoplasmic extensions of the neutrophils.     

Inhibition of insect development by simultaneous action of prothoracic gland hormone and juvenile hormone

Injections of large amounts (around 20 μg) of ecdysterone and of Cecropia C₁₇-juvenile hormone or its bio-analogue 6,7-epoxygeranyl 3,4-methylendioxyphenyl ether into a pupa of Tenebrio molitor may inhibit the apolysis and cuticle secretion. Some of the treated insects secrete a new cuticle only locally, others do not even undergo apolysis although they survive until the controls ecdyse as adults. The development of internal organs is also hindered. These results are tentatively explained in terms of a mutually antagonistic action of the two hormones on nucleic acid synthesis.     

The nucellus: between cell elimination and sugar transport

The architecture of the seed is shaped by the processes of tissue partitioning, which determines the volume ratio of maternal and zygotic tissues, and nutrient partitioning, which regulates nutrient distribution among tissues. In angiosperms, early seed development is characterized by antagonistic development of the nucellus maternal tissue and the endosperm fertilization product to become the main sugar sink. This process marked the evolution of angiosperms and outlines the most ancient seed architectures. In Arabidopsis, the endosperm partially eliminates the nucellus and imports sugars from the seed coat. Here, we show that the nucellus is symplasmically connected to the chalaza, the seed nutrient unloading zone, and works as both a sugar sink and source alongside the seed coat. After fertilization, the transient nucellus accumulates starch early on and releases it in the apoplasmic space during its elimination. By contrast, the persistent nucellus exports sugars toward the endosperm through the SWEET4 hexose facilitator. Finally, we analyzed sugar metabolism and transport in the transparent testa 16 mutant, which fails to undergo nucellus cell elimination, which shed light on the coordination between tissue and nutrient partitioning. Overall, this study identifies a path of sugar transport in the Arabidopsis seed and describes a link between sugar redistribution and the nucellus cell-elimination program.

A path of sugar transport through the nucellus maternal tissue of the Arabidopsis seed is coordinated with the process of nucellus cell elimination.     

Ultrastructure of excretory system in <Emphasis Type="Italic">Bothrioplana semperi</Emphasis> (Platyhelminthes,Turbellaria)

The ultrastructure of flame bulbs and epithelium of excretory canals in Bothrioplana semperi (Turbellaria, Seriata) have been studied. The flame bulbs consist of two cells, the terminal cell and the proximal canal cell. The weir is formed by two rows of longitudinal ribs. The ribs of the internal row originate from the flame cell, external ribs are formed by the proximal canal cell. Each external rib has a remarkable bundle of microfilaments, originating in the cytoplasm of the first canal cell distally to the bases of external ribs. Membrane of internal ribs is marked by small electrondense granules, separate or fused to an electron-dense layer, continuous to dense “membrane,” connecting both external and internal ribs. Sparse internal leptotrichs originate from the bottom of the flame bulb cavity. External leptotrichs are lacking. Septate junction is present only in proximal canal cell at the level of tips of cilia. The apical surface of the canal cell bears rare short microvilli. The basal membrane of canal cells forms long invaginations that may reach nearly the apical membrane. The epithelium of excretory canals lacks the cilia. The ultrastructure of flame bulbs and epithelium of the excretory canals in B. semperi shares representatives of suborder Proseriata (Seriata). The contradiction exists in interpretation of the structure of flame bulbs in Proseriata. Ehlers and Sopott-Ehlers assumed that the external ribs are derivatives of the proximal canal cell and internal ones are outgrowths of the terminal cell, while Rohde has found conversely: the external ribs are outgrowths of the terminal cell, the internal ones are outgrowths of the proximal canal cell. However, the illustrations provided by Rohde do not enable to ascertain what cells the internal and external ribs derive from, while illustrations provided by Ehlers justify his interpretation. The order of weir formation in B. semperi confirms the viewpoint of Ehlers. The implication of ultrastructure of flame bulbs in Proseriata, especially of the order of flame bulb formation, in the Platyhelminthes phylogeny has been discussed.     

Worms under Pressure: Bulk Mechanical Properties of C. elegans Are Independent of the Cuticle

The mechanical properties of cells and tissues play a well-known role in physiology and disease. The model organism Caenorhabditis elegans exhibits mechanical properties that are still poorly understood, but are thought to be dominated by its collagen-rich outer cuticle. To our knowledge, we use a novel microfluidic technique to reveal that the worm responds linearly to low applied hydrostatic stress, exhibiting a volumetric compression with a bulk modulus, κ = 140 ± 20 kPa; applying negative pressures leads to volumetric expansion of the worm, with a similar bulk modulus. Surprisingly, however, we find that a variety of collagen mutants and pharmacological perturbations targeting the cuticle do not impact the bulk modulus. Moreover, the worm exhibits dramatic stiffening at higher stresses—behavior that is also independent of the cuticle. The stress-strain curves for all conditions can be scaled onto a master equation, suggesting that C. elegans exhibits a universal elastic response dominated by the mechanics of pressurized internal organs.