Ovule and seed ontogeny inGnetum gnemon L.

Takaso, Tokushiro; Bouman, F.

doi:10.1007/bf02489542

Cited by 43 publications

(46 citation statements)

References 17 publications

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“…In the Gnetales, vascular bundles are absent in the integument but present in the seed envelopes [24], which supports our interpretation that the supportive strands of Siphonospermum are originally derived from the seed envelope.…”

Section: Discussionsupporting

confidence: 83%

A new Early Cretaceous relative of Gnetales: Siphonospermum simplex gen. et sp. nov. from the Yixian Formation of Northeast China

Rydin

Friis

2010

BMC Evol Biol

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BackgroundKnowledge on fossil and evolutionary history of the Gnetales has expanded rapidly; Ephedra and ephedroids as well as the Gnetum-Welwitschia clade are now well documented in the Early Cretaceous. However, hypotheses on evolutionary relationships among living and fossil species are hampered by restricted knowledge of morphological variation in living groups and recent studies indicate that gnetalean diversity and character evolution may be more complex than previously assumed and involve additional extinct groups (Bennettitales, Erdtmanithecales and unassigned fossil taxa).ResultsHere we describe a new fossil related to Gnetales, Siphonospermum simplex from the Early Cretaceous Yixian Formation, an impression/compression of a reproductive shoot. The slender main axis bears one pair of opposite and linear leaves with primary parallel venation. The reproductive units are ovoid, without supporting bracts and borne on one median and two lateral branches. The most conspicuous feature of the fossil is the long, thread-like micropylar tube formed by the integument. Each ovule is surrounded by two different layers representing one or two seed envelopes; an inner sclerenchymatous layer and an outer probably parenchymatous layer.ConclusionsThe vegetative and reproductive features of Siphonospermum simplex exclude a relationship to any other group than the Gnetales. A combination of opposite phyllotaxis, linear leaves and ovules surrounded by seed envelope(s) and with a long exposed micropylar tube are known only for extant and extinct Gnetales. Siphonospermum simplex constitutes a new lineage within the Gnetales. Its morphology cannot be directly linked to any previously known plant, but the organization of the reproductive units indicates that it belongs to the Gnetum-Welwitschia clade. Based on the absence of cone bracts and the inferred histology of the seed envelope(s) it could be related to Gnetum, however, there are also affinities with the ephedran lineage, some of which are likely plesiomorphic features, others perhaps not. Phylogeny and character evolution in the Bennettitales, Erdtmanithecales and Gnetales are currently only partly understood and under debate; the exact systematic position of Siphonospermum simplex, i.e., its position within the Gnetales, cannot be resolved with certainty.

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Section: Discussionsupporting

confidence: 83%

A new Early Cretaceous relative of Gnetales: Siphonospermum simplex gen. et sp. nov. from the Yixian Formation of Northeast China

Rydin

Friis

2010

BMC Evol Biol

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“…In panels C, G, K and O, hybridization was done with sense probes obtained from the GGM13 cDNA (negative controls). The schematic drawings in D, H, L and P designate the different organs which are formed during the ontogeny of the G. gnemon strobilus (cone) and ovule (according to Takaso and Bouman 1986). A-D Longitudinal sections of a very young strobilus.…”

Section: Discussionmentioning

confidence: 99%

A novel MADS-box gene subfamily with a sister-group relationship to class B floral homeotic genes

et al. 2002

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Class B floral homeotic genes specify the identity of petals and stamens during the development of angiosperm flowers. Recently, putative orthologs of these genes have been identified in different gymnosperms. Together, these genes constitute a clade, termed B genes. Here we report that diverse seed plants also contain members of a hitherto unknown sister clade of the B genes, termed B(sister) (B(s)) genes. We have isolated members of the B(s) clade from the gymnosperm Gnetum gnemon, the monocotyledonous angiosperm Zea mays and the eudicots Arabidopsis thaliana and Antirrhinum majus. In addition, MADS-box genes from the basal angiosperm Asarum europaeum and the eudicot Petunia hybrida were identified as B(s) genes. Comprehensive expression studies revealed that B(s) genes are mainly transcribed in female reproductive organs (ovules and carpel walls). This is in clear contrast to the B genes, which are predominantly expressed in male reproductive organs (and in angiosperm petals). Our data suggest that the B(s) genes played an important role during the evolution of the reproductive structures in seed plants. The establishment of distinct B and B(s) gene lineages after duplication of an ancestral gene may have accompanied the evolution of male microsporophylls and female megasporophylls 400-300 million years ago. During flower evolution, expression of B(s) genes diversified, but the focus of expression remained in female reproductive organs. Our findings imply that a clade of highly conserved close relatives of class B floral homeotic genes has been completely overlooked until recently and awaits further evaluation of its developmental and evolutionary importance. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00438-001-0615-8.

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“…Excluding cycads, other gymnosperms do not show the same extensive demarcation of a flattened-cell layer surrounding the sporogenous tissue so early in development. Anticlinal divisions in the hypodermal layer at the nucellusintegument border occur in Ephedra (Takaso 1985) and Gnetum (Takaso and Bouman 1986), but their flattened-cell layer extends only two to five cells under the nucellar tissue and occurs later in development. In conifers, this pattern is also present, but the flattened cells extend only one or two layers down (e.g., Buchholz 1941;Kemp 1959;Tomlinson et al 1989;Takaso and Tomlinson 1991).…”

Section: Ovulementioning

confidence: 97%

“…The nucellar cap in Ginkgo contributes to the pollen chamber. In other taxa, longitudinal axial patterns of cells can be linked to periclinal divisions in the epidermal layer and constitute a nucellar cap (Gnetales: Singh and Maheshwari 1962;Takaso and Bouman 1986; reconstruction in Cycadeoidea: Crepet and Delevoryas 1972;Williamsonia: Sharma 1974). There is, however, contradictory evidence regarding a nucellar cap in some taxa, including Taxus (Dupler 1917;Pankow 1962).…”

Section: Secondary Parietal Tissuesmentioning

confidence: 99%

“…A distinct epidermal layer is common among many gymnosperms, including Zamia (Fagerlind 1961(Fagerlind , 1971, some Ephedra species (Singh and Maheshwari 1962), and others, although there is some level of conflict in the literature (see Singh 1978). In some taxa, such as Taxus (Dupler 1917;Pankow 1962) and Gnetum (Takaso and Bouman 1986), derivatives of periclinal divisions in the epidermal layer contribute to the parietal tissue and form the nucellar cap. The timing of periclinal divisions in the epidermis varies among taxa with nucellar caps, although in some, the epidermis contributes to the parietal tissue as the primary nucellar tissues are developing.…”

Section: Secondary Parietal Tissuesmentioning

confidence: 99%

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Ovule Development inGinkgo bilobaL., with Emphasis on the Collar and Nucellus

Douglas

Stevenson

Little

2007

International Journal of Plant Sciences

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Ovule development in Ginkgo biloba is examined. Ovulate stalks are initiated in leaf axils, and each stalk primordium dichotomizes to produce two ovule primordia. Integument development appears circumferential and during micropyle formation becomes slightly lobed. Primary nucellar tissues are derived from periclinal divisions in the hypodermal layer, which is limited to several apically located cells of the nucellus and remains active through pollen chamber formation. One spore mother cell differentiates in the sporangial tissues; others differentiate as tapetum. The epidermal layer does not contribute directly to development of the primary nucellus but does contribute to secondary nucellar tissues. Secondary parietal tissues are divided into regions based on their growth patterns and location within the nucellus: the pollen chamber, including a distinct exothecium; the micropylar parietal tissue, including the distal and proximal tissues; the flanking parietal tissue; and the chalazal parietal tissue that lies between the flattened-cell layer and the enlarging sporogenous tissue. The collar develops from periclinal divisions of cells in the hypodermal layer proximal to the ovule after the integument and nucellus have differentiated. The collar is interpreted as a unique structure within ginkgophytes. In some ovules, an organized flap of tissue develops between the collar and the ovule. There does not seem to be any homology of the flap with other structures in gymnosperms based on position or timing of growth, and it is interpreted as a structure sui generis.

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Ovule and seed ontogeny inGnetum gnemon L.

Cited by 43 publications

References 17 publications

A new Early Cretaceous relative of Gnetales: Siphonospermum simplex gen. et sp. nov. from the Yixian Formation of Northeast China

A new Early Cretaceous relative of Gnetales: Siphonospermum simplex gen. et sp. nov. from the Yixian Formation of Northeast China

A novel MADS-box gene subfamily with a sister-group relationship to class B floral homeotic genes

Ovule Development inGinkgo bilobaL., with Emphasis on the Collar and Nucellus

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