Valve Margin Research Articles

The Role of the REPLUMLESS Homeodomain Protein in Patterning the Arabidopsis Fruit

The outside of the Arabidopsis thaliana fruit consists of three principal tissues: the valves or seedpod walls, the replum or central ridge between the valves, and the valve margins where the valves separate from the replum to disperse the seeds. Previous studies have shown that valve margin formation is specified by the SHATTERPROOF MADS-box transcription factors [1] and that valve development is controlled by the FRUITFULL MADS-box transcription factor [2]. FRUITFULL negatively regulates SHATTERPROOF to prevent the valves from adopting a valve margin cell fate [3]. Here we identify a gene called REPLUMLESS that is required for replum development. REPLUMLESS encodes a homeodomain protein that prevents replum cells from adopting a valve margin cell fate by negatively regulating expression of the SHATTERPROOF genes. Both REPLUMLESS and FRUITFULL are required to limit SHATTERPROOF expression to a narrow stripe of cells so that the valve margin differentiates precisely at the valve/replum boundary.

Defective valvulogenesis in HB-EGF and TACE-null mice is associated with aberrant BMP signaling.

Heparin-binding epidermal growth factor (HB-EGF) and betacellulin (BTC) are activating ligands for EGF receptor (EGFR/ErbB1) and ErbB4. To identify their physiological functions, we disrupted mouse HB-EGF and BTC alleles by homologous recombination. Most HB-EGF(-/-) mice died before weaning, and survivors had enlarged, dysfunctional hearts and reduced lifespans. Although BTC(-/-) mice were viable and fertile and displayed no overt defects, the lifespan of double null HB-EGF(-/-)/BTC(-/-) mice was further reduced, apparently due to accelerated heart failure. HB-EGF(-/-) newborns had enlarged and malformed semilunar and atrioventricular heart valves, and hypoplastic, poorly differentiated lungs. Defective cardiac valvulogenesis was the result of abnormal mesenchymal cell proliferation during remodeling, and was associated with dramatic increases in activated Smad1/5/8. Consistent with the phenotype, HB-EGF transcripts were localized to endocardial cells lining the margins of wild-type valves. Similarly defective valvulogenesis was observed in newborn mice lacking EGFR and tumor necrosis factor-alpha converting enzyme (TACE). These results suggest that cardiac valvulogenesis is dependent on EGFR activation by TACE-derived soluble HB-EGF, and that EGFR signaling is required to regulate bone morphogenetic protein signaling in this context.

MORPHOLOGICAL OBSERVATIONS OF NEIDIUM SPECIES WITH SAGITTATE APICES, INCLUDING THE DESCRIPTION OF N. CAPE-CODII SP. NOV.

Nedium cape-codii Siver & Hamilton sp. nov. is described from a small glacial kettle lake situated on the Cape Cod peninsula, Massachusetts, U.S.A. Nedium cape-codii is a large diatom with slightly bowed margins, a single longitudinal canal along each valve margin and sagittate apices. Each areola is covered externally by volae and internally with a flat, thin, perforated hymen. In addition, small kidney bean-shaped structures, termed here renilimbi, are associated with specific rows of areolae on the internal valve surface. We also present SEM-based morphological descriptions of N. tokyoense Kobayasi, N. pseudogracilis Kobayasi and N. gracile Hustedt, the three species with sagittate apices morphologically most similar to N. cape-codii, from either type material or new material collected from the type localities. The relationships of N. cape-codii to other species with sagittate apices are also discussed.

Morphology of Prorocentrum minimum (Dinophyceae) in the Baltic Sea and in Chesapeake Bay: Comparison of Cell Shapes and Thecal Ornamentation

Prorocentrum minimum (Dinophyceae) is a red tide-forming toxin-producing planktonic microalga from coastal waters worldwide. In this study, the morphology of natural and cultured populations of P. minimum was examined to investigate whether the species can be split morphologically into more species. The diacritical features of cell shape and size, ornamentation of thecal plates, and architecture of the apical pore area and intercalary band were studied from scanning and light micrographs. Cell size of P. minimum is similar in Baltic Sea samples and a culture from the Chesapeake Bay, USA. Cell shape varies from triangular to oval-round including intermediate forms in valve view. The thecal surface is covered by evenly distributed short spines, while the circular thecal pores are mainly situated near the valve margin. The intercalary band is rim-like, striated and covered with short evenly distributed spines. The architecture of the apical pore area is ornate and more complex than previously pointed out. It is V-shaped, located on the right valve in a shallow depression and accommodates a large elongated flagellar pore, and a small round auxiliary pore. Four distinct apical features are present: next to the auxiliary pore there is a curved collar, and adjacent to the flagellar pore arise a forked double tooth, a short single tooth, and a ridged edge near the left valve margin. Our study suggests that the ornamentation of the apical pore area of P minimum is independent of cell shape or growth place, and it is considered a stable morphological character of this cosmopolitan morphospecies.

Heterocypris (Crustacea, Ostracoda) from the Isole Pelagie (Sicily, Italy): Population genetics

We analysed the genetic structure of five populations of Heterocypris from small temporary ponds on the islands of Lampedusa and Linosa (Isole Pelagie, South of Sicily) where we have observed two different adult females morphotypes. The most genetically‐differentiated population, Cavallo Bianco, is made up by females only showing a morphology typical of H. incongruens. All other populations, from both islands, are bisexual and their adult females present a lobe‐like expansion of the selvage (lamella hyalina) on the posterior margin of the left valve. In one locality, Vallone della Forbice, both female morphotypes occur. The analyses of individuals raised in the laboratory microcosms confirmed the genetic differentiation between morphotypes and their different reproductive modes. The adult females without a lamella hyalina are apomictic, whereas females with this feature are am‐phimictic. Genetic differentiation of the two female morphotypes is compatible with the hypothesis that the two morphotypes represent different species of Heterocypris although, such a morphological differentiation is not unusual in populations of the same parthenogenetic species, and we found evidence of hybridisation between males and parthenogenetic females.

On The Stability Margin of Hole-Entry Hybrid Journal Bearings Considering Viscosity-Temperature Variation

The present study describes the theoretical investigation into the stability margin of a constant flow valve compensated hole-entry hybrid journal bearing system considering the variation of viscosity due to temperature rise of the lubricant. The journal temperature is computed on the basis of average fluid-film temperature. The relevant governing equations are solved using a finite element method and a suitable iterative technique. The thermohydrostatic performance of symmetric and asymmetric hole-entry hybrid journal bearing configurations are studies. The results presented in the study indicate that the variation of viscosity due to temperature rise of the lubricant fluid-film affects the performance of hole-entry hybrid journal bearing system quite significantly.

VALVE MORPHOGENESIS IN THE MARINE ARAPHID DIATOM GEPHYRIA MEDIA (BACILLARIOPHYCEAE)

Valve morphogenesis in the marine araphid diatom Gephyria media W. Arnott was studied using dense populations epiphytic on red algae. Valves begin as a narrow sternum with virgae (pinnate lateral outgrowths). The apical pore fields and rimoportulae at each end of the concave valve are produced early in valve morphogenesis. The rimoportulae of the convex valve are also formed early and the virgae are branched at the apex. The timing of rimoportula formation well after formation of the virgae appears to contradict the hypothesis that the raphe system may have evolved from rimoportulae of araphid diatoms. Formation of the bi- and triseriate striae begins at the sternum with the lateral outgrowth of forked vimines, which then fuse. Completion of valve morphogenesis involves the development of an internal silica sheet. When the sheet is fully extended it forms an internal zigzag pattern of foramina near the valve margin in both kinds of valves, thus producing chambers. The rimoportula lengthens internally and in the final process forms the labiate process upon a stalk. Delicate internal rotae were observed in mature valves. Several features of valve morphogenesis in G. media are similar to those observed in other araphid and raphid species. The apical pore field develops in a manner similar to that of Gomphonema, the chambering as in Pinnularia and Catacombas and the rimoportula as in Diatoma.

A NOTE ON THE VALVE STRUCTURE OF TRICERATIUM HETEROGONUM BARKER & MEAKIN, AN UNUSUAL SPECIES FROM CONSET, BARBADOS

The valve structure of Triceratium heterogonum Barker & Meakin is basically quadrate in which two opposing angles have gently rounded apices while the other two angles are slightly more acute. The valve margin between the angular extensions is concave. Each valve has two types of processes, a single process lying within each angle, those of opposing angles identical. Lying within the broader and more rounded angle is a hyaline tubular structure, directed outwards, and terminating in a cup-like structure; at the other pole a shorter elevation terminating in a thickened hyaline rim. A detailed description of the valve structure and processes is given, comparisons of the tubular structure made with those of other genera and a discussion on relationships with other genera, particularly that with Triceratium sensu stricto, is also given. A new genus Petrochiscus is proposed with T. heterogonum as the generitype.

Guangnania cuneata gen. et sp. nov. from the Lower Devonian of Yunnan Province, China

Guangnania cuneata gen. et sp. nov. has been collected from the Lower Devonian (Pragian) Posongchong Formation of southeast Yunnan and the (Pragian-early Emsian) Xujiachong Formation of east Yunnan, China. The plant possesses dichotomous branches. The fertile region consists of lateral sporangia attached helically. Each sporangium is elongate cuneate and long-stalked. It dehisces into two unequal valves, a large abaxial valve and a small adaxial one, which in transverse section are curved towards the axis. The dehiscence line is bordered by the thickening along the entire sporangial valve margin. The elongate, curved shape and unequal valves of the long-stalked lateral sporangia make this plant a new genus. We suggest that morphological variation in the zosterophylls includes the sporangial shape, i.e. reniform, rounded/globose to vertically elongate. On this basis, the lateral sporangial position and the sporangial rim bordering the dehiscence line, Guangnania may be provisionally allied to the zosterophylls, although stelar anatomy is unknown. The common occurrence of Zosterophyllum australianum Lang et Cookson 1930, Huia Geng 1985 and this new plant during the Early Devonian (Pragian) suggests that the Posongchong flora and mid-lower assemblage of the Xujiachong flora show some similarities in composition and coeval. The disparity in these two floras is probably due to different environments in which plants lived and were preserved.

Prorocentrum nux sp. nov. (Dinophyceae), a small planktonic dinoflagellate from the Mediterranean Sea, and discussion of P. nanum and P. pusillum

A new Prorocentrum species was discovered in the Gulf of Naples (Mediterranean Sea) and is described in the present study as P. nux Puigserver & Zingone sp. nov. Prorocentrum nux is small (6.3–9.0 μm long, 5.3–10.0 μm wide, and 5.3–10.7 μm deep), irregularly oval in valve view, and lacks an apical spine. Unlike most Prorocentrum species, its cells are not laterally compressed, owing to the marked convexity of the valves and to the overgrowth of the intercalary bands. The thecal plates are thin and smooth, with a few pores of two different sizes near the valve margins. Seven platelets are arranged around the flagellar pore. Two parietal chloroplasts are present, each having a pyrenoid without a visible starch shield. The nucleus is located posteriorly. A pusule is present close to the flagellar bases. Numerous trichocysts were observed both within the cell and discharged outside it. In the genus Prorocentrum, two other small-celled species have been described, viz. P. nanum and P. pusilium; the latter has sometimes been considered a synonym of the former. However, based on their original descriptions and on other published information, P. nanum and P. pusillum are quite distinct from each other and from P. nux, with respect to cell shape, and the size and location of the thecal pores. Unlike P. nux, both P. nanum and P. pusillum are described as having a thick theca and a laterally flattened cell body. We reexamined the only existing culture material classified as P. nanum, viz. UTEX LB 1008, derived from the Plymouth 184 strain and originally identified as Exuviaella pusilla. This material has consistently been misidentifiedand has the same distinctive characters as P. nux.

Heterocypris (Crustacea, Ostracoda) from the Isole Pelagie (Sicily, Italy): The coexistence of different morphotypes

Differences exist in the population structure of Heterocypris in five temporary ponds on the islands of Lampedusa and Linosa (Isole Pelagie, south of Sicily). In a temporary pond on Lampedusa (Cavallo Bianco) we found only H. incongruens females. All the other populations were bisexual, with the female/male sex ratio varying from 1 to 18. We analysed and measured a sub‐sample from each population and observed, as a typical morphological feature of adult females in the bisexual populations, a lobe‐like expansion of the selvage (lamella hyalina) on the posterior margin of the left valve. In another temporary pond from Lampedusa (Vallone della Forbice) both females with this lamella and others without it occur. We discuss the possible coexistence of two lineages of H. incongruens each having a different reproductive mode. The parthenogenetic lineage comprises females without a lamella hyalina whereas the bisexual females possess this feature. Alternatively, we hypothesise the sympatry of two different species of Heterocypris: H. incongruens and H. barbara. In this hypothesis, H. incongruens is parthenogenetic and H. barbara is amphimictic. Differences in mean body size between the adult females with and without the lamella hyalina are in accordance with values reported in the literature for niche differentiation among sympatric taxa.

The Arabidopsis myc/bHLH gene ALCATRAZ enables cell separation in fruit dehiscence

Background: Several processes of plant development, such as abscission, pollen release, fruit dehiscence, and seed dispersal, require organs or tissues to physically disassociate or split open. Due to the immobility of plant cells, these processes occur through coordinated mechanisms of cell separation that are not found in animals. Arabidopsis produces dry dehiscent fruits (siliques) making it a convenient system for the genetic study of cell separation associated with dehiscence.Results: We describe here a novel mutation in Arabidopsis called alcatraz (alc), which prevents dehiscence of fruit by specifically blocking the separation of the valve cells from the replum. The ALC gene is shown to encode a protein related to the myc/bHLH family of transcription factors and is expressed in the valve margins of the silique, which is the site of cell separation during dehiscence. Detailed studies using TEM indicates that ALC enables cell separation in Arabidopsis fruit dehiscence by promoting the differentiation of a strip of labile nonlignified cells sandwiched between layers of lignified cells. Transgenic plants expressing antisense or dominant-negative ALC are defective in silique dehiscence.Conclusions: Cell separation in fruit dehiscence requires a specialized cell layer which is nonlignified and capable of autolysis, specified by a myc/bHLH protein encoded by ALC. These findings may have relevance to other processes requiring cell separation, as well as for the practical design of crops with reduced seed losses.

PSAMMOCOCCONEIS, A NEW GENUS OF BACILLARIOPHYTA FROM BRAZILIAN SANDY BEACHES

The new genus is characterised by the presence of a valvocopula with straight and smooth margins and by round and transapically elongated pores on its surface. The valvocopula fits beneath the raphe valve and covers the valve areolae and even sometimes the raphe. The internal and external raphe ends are simple. The areolae are occluded by fine porous hymenes on the raphid valve and they are coarser on the araphid valve. Two types of areolae are present around the margin of the araphid valve. The new genus is described from Brazilian sandy beaches (Porto Belo, Brazil) and Cocconeis disculoides Hustedt is transferred to Psammococconeis, establishing a new combination.

A new genus for isolated bivalved sporangia with thickened margins from the Lower Devonian of the Welsh Borderland

A new taxon Sporathylacium salopense gen. et sp. nov. is based on small isolated coalified sporangia from the Lower Devonian (Lochkovian micrornatus – newportensis spore zone) from the Welsh Borderland. The sporangia have two equal valves with multi-layered walls and thickened borders, and contain trilete crassitate, non-curvaturate isospores that are completely covered by a microgranular ornament with possible distal verrucate/murornate structures. They differ from zosterophyll sporangia in details of the presumed dehiscence zone extending around the entire free convex margin, particularly in the presence of a wedge of amorphous material between the valves, and in spore characters. Absence of any information relating to water-conducting cells prevents further assignment within the embryophytes. Spherical bodies associated with spores and a resilient sporangial lining are compared with similar structures in extant free-sporing plants and with Ubisch bodies. The mode of sporangial dehiscence involving anatomical modifications of the valve margins and the novel wedge of tissue which connects them remains speculative.

A new genus for isolated bivalved sporangia with thickened margins from the Lower Devonian of the Welsh Borderland

A new taxon Sporathylacium salopense gen. et sp. nov. is based on small isolated coalified sporangia from the Lower Devonian (Lochkovian: micrornatus—newportensis spore zone) from the Welsh Borderland. The sporangia have two equal valves with multi-layered walls and thickened borders, and contain trilete crassitate, non-curvaturate isospores that are completely covered by a microgranular ornament with possible distal verrucate/murornate structures. They differ from zosterophyll sporangia in details of the presumed dehiscence zone extending around the entire free convex margin, particularly in the presence of a wedge of amorphous material between the valves, and in spore characters. Absence of any information relating to water-conducting cells prevents further assignment within the embryophytes. Spherical bodies associated with spores and a resilient sporangial lining are compared with similar structures in extant free-sporing plants and with Ubisch bodies. The mode of sporangial dehiscence involving anatomical modifications of the valve margins and the novel wedge of tissue which connects them remains speculative.

The MADS-box gene DEFH28 from Antirrhinum is involved in the regulation of floral meristem identity and fruit development.

DEFH28 is a novel MADS-box gene from Antirrhinum majus. Phylogenetic reconstruction indicates that it belongs to the SQUA-subfamily of MADS-box genes. Based on its expression pattern and the phenotype of transgenic plants it is predicted that DEFH28 exerts a dual function during flower development, namely control of meristem identity and fruit development. Firstly, DEFH28 is expressed in the inflorescence apical meristem and might control, together with SQUAMOSA (SQUA), floral meristem identity in Antirrhinum. Also, DEFH28 is sufficient to switch inflorescence shoot meristem to a floral fate in transgenic Arabidopsis thaliana plants. Secondly, DEFH28 is expressed in carpel walls, where it may regulate carpel wall differentiation and fruit maturation. Support for this later role comes from overexpression of DEFH28 throughout the silique in transgenic Arabidopsis plants where it altered the identity of the replum and valve margin cells so that they adopted a valve cell identity. This late aspect of the DEFH28 function is identical to the FRUITFULL (FUL) function of Arabidopsis as demonstrated in gain-of-function plants. FUL, like DEFH28, belongs to the SQUA-subfamily of MADS-box genes. DEFH28 most likely represents the ortholog of FUL. Promoter analysis shows that the control mechanism conferring a carpel wall specific expression has been conserved between Antirrhinum and Arabidopsis during evolution. Although the overall flower development between Antirrhinum and Arabidopsis is very similar, their carpels mature into different types of fruits: capsules and siliques, respectively. Therefore, it is suggested that the role of DEFH28 in control of carpel wall differentiation reflects a conserved molecular mechanism integrated into two very different carpel developmental pathways.

A new marine diatom, Cocconeis shikinensis sp. nov. (Bacillariophyceae) from Japan

SUMMARY A new species of Cocconeis has been found growing on the green seaweed Caulerpa racemosa (Forsskal) J. Agardh var. laete-virens (Montagne) Weber van Bosse from Shikine Island in the Izu Islands on the Pacific coast of Japan; we propose the name Cocconeis shiki-nensis Hid. Suzuki and describe the species by light microscopy (LM) and electron microscopy (EM). This taxon was also collected from the plastic plates used for rearing in seed production systems of the abalone Nordotis discus hannai Ino and the horned turban Turbo cornutus Solander in the Toyama Prefectural Fisheries Research Institute facing the Sea of Japan. The main morphological features of C. shikinensis are as follows. The valves are elliptic. The valve face of the raphid valve (RV) is slightly concave and that of the araphid valve (AV) is complementary to the RV and convex. The single plastid is flat, C-shaped and elaborately lobed. The raphe on the RV is straight. The each terminal area expands to both sides along the valve margin, forming an arrowhead-shaped, thickened hyaline area. The striae consist of small, round areolae and are radiate and uniseriate. On the AV, the striae consist of several alveoli. Each alveolus opens internally by means of a circular foramen. The valvocopula of each valve is fimbriate and open. The cingulum attached to the AV consists of three girdle bands; a valvocopula and two bands (copula and pleura), which are open and have ligulae. The relationship between C. shikinensis and similar members of the genus Cocconeis is discussed.

TAXONOMY OF THE THALASSIOSIRA TRIFULTA GROUP IN LATE NEOGENE SEDIMENTS FROM THE NORTHWEST PACIFIC OCEAN

Several lower Miocene, Pliocene, and Pleistocene samples from the northwest Pacific Ocean were used to study the taxonomy of the Thalassiosira trifulta group, which is characterized by the inward tubes of the fultoportulae and a rimoportula located away from the valve margin. T. ferelineata, T. frenguelliopsis, T. tetraoestrupii, and Thalassiosira sp. A (referred to as the T. frenguelliopsis subgroup) were found to have operculate fultoportulae with an operculate basal structure covering the 4 satellite pores in the basal siliceous membrane. A second subgroup, consisting of T. oestrupii, T. praeoestrupii, and T. trifulta (referred to as the T. oestrupii subgroup), have a trifultate fultoportula with 3 columnar supports and 3 satellite pores. In T. praeoestrupii sensu stricto the trifultate fultoportula is intermediate in structure with 3 columnar supports and an operculate basal structure covering the 3 satellite pores.

MORPHOLOGY AND TAXONOMY OF EUNOTIA CLEVEI

Eunotia clevei Grunow ex Cleve was collected as an epiphyte on aquatic mosses and macroalgae from the Ravdangiin Bulag mineral spring in western Mongolia. E. clevei is widely reported but usually rare in many north temperate large-lake systems and fossil deposits. This taxon is characterized by its large size, two rimoportulae per valve, a small pseudoseptum that is overlapped by die valvocopula, spinules on the dorsal and ventral valve margins, an internal proximal raphe hook, sternum on the valve face, coarsely areolate striae in LM, and epithemioid frustular symmetry (heteropolarity in the transapical plane) because of dorsalty expanded mantles and cingular elements. This combination of characters clearly differentiates E. clevei from Eunotia sensu stricto;, however, some of these characters are shared with other eunotioid genera such as Desmogonium, Semiorbis, Peronia, Actinella, and Eunophora, suggesting that Eunotia clevei, its varieties, and allied taxa may be better placed within a new genus.

The archaeological remains of leucaena (Fabaceae) revised

Archaeological specimens of Leucaena (Fabaceae; Mimosoideae) previously published (Tamaulipas, Tehuacan Valley, and Oaxaca Valley) which are housed at the Departmento de Prehistoria, Instituto Nacional de Antropologia e Historia, Mexico City, were reexamined. Selected remains from Tehuacan were observed with scanning electron microscopy and ultrastructural features were compared to material from herbarium specimens. External epidermis near margins of legume valves provided identification characteristics (stomata abundance and morphology, texture, pubescence). In Tehuacan, L. leucocephala subsp. glabrata was found in addition to two previously reported taxa—L. esculenta and L. diversifolia subsp. stenocarpa (L. pueblana). Acacia sericea, a wild tree with edible legumes, was frequently misidentified as Leucaena. In Guila Naquitz, Oaxaca, all samples reported as L. esculenta were identified as another edible, wild legume tree, Conzatia multiflora. Chronology was assigned following published reports and, also for Tehuacan, the field catalogue. Possible use was assigned based upon evidence of chewing and insect damage, indicating ripeness of legumes. No direct evidence of cultivation was found. However, the presence of L. esculenta in Tehuacan (since ca. 4000-1000 B.C.) and of L. I. glabrata (since ca. 300 B.C.-A.D. 780) suggests their introduction there as a cultivated plant.