Embryology: Then and Now

Johri, B. M.; Ambegaokar, Kunda B.

doi:10.1007/978-3-642-69302-1_1

“…This agrees with the observations that embryos of many plant species, such as cotton, grape, and Dafura (Johri, 1984), as well as Arabidopsis mutant fass embryos (Torres Ruiz and Jürgens, 1994), do not show an ordered pattern of early cell division yet develop complete body plans with all pattern elements present.…”

Section: Embryos: Lmplications For Pattern Formation In the Arabidopssupporting

confidence: 90%

Pattern Formation in the Arabidopsis Embryo Revealed by Position-Specific Lipid Transfer Protein Gene Expression.

Vroemen¹,

Langeveld²,

Mayer³

et al. 1996

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During Arabidopsis embryogenesis, the zygote divides asymmetrically in the future apical-basal axis; however, a radial axis is initiated only within the eight-celled embryo. Mutations in the GNOM, KNOLLE, and KEULE genes affect these processes: gnom zygotes tend to divide symmetrically; knolle embryos lack oriented cell divisions that initiate protoderm formation; and in keule embryos, an outer cell layer is present that consists of abnormally enlarged cells from early development. Pattern formation along the two axes is reflected by the position-specific expression of the Arabidopsis lipid transfer protein (AtLTPT) gene. In wild-type embryos, the AtLTPl gene is expressed in the protoderm and initially in all protodermal cells; later, AtLTPí expression is confined to the cotyledons and the upper end of the hypocotyl. Analysis of AtLTPT expression in gnom, knolle, and keule embryos showed that gnom embryos also can have no or reversed apical-basal polarity, whereas radial polarity is unaffected. knolle embryos initially lack but eventually form a radial pattern, and keule embryos are affected in protoderm cell morphology rather than in the establishment of the radial pattern. INTRODUCTIONIn flowering plants, the primary body plan of the seedling is laid down during embryogenesis (Steeves and Sussex, 1989). This body plan has been described as the superimposition of an apical-basal and a radial pattern . The apical-basal pattern visible in the seedling consists of distinct elements: two cotyledons, shoot meristem, hypocotyl, and root, including the root meristem. In Arabidopsis, the apical-basal polarity is already evident in the zygote, which elongates approximately threefold in the apical direction. An asymmetric division then generates a small apical cell from which all pattern elements are derived, except for part of the root, that is, the columella root cap and the quiescent center (Scheres et al., 1994), and the suspensor, which are derived from the larger basal cell. Mutations resulting in a deletion of regions of the apical-basal pattern include gurke, fackel, monopteros, and gnom (Mayer et al., , 1993 Berleth and Jürgens, 1993) and rootless, shoot meristemless, and topless (Barton and Poethig, 1993).In gnom embryos (Mayer et al., , 1993Busch et al., 1996), also called emb30 embryos (Shevell et al., 1994;Franzmann et al., 1995), the zygote tends to divide symmetrically, producing an enlarged apical cell at the expense of the basal cell. gnom embryos have no root meristem and reduced orno cotyledons, and most gnom seedlings are cone shaped, 'To whom correspondence should be addressed.retaining apical-basal polarity, although the pattern is severely compromised. Some gnom seedlings, however, are ball shaped, displaying no morphologically apparent apical-basal polarity (Mayer et al., 1993). The radial pattern is arranged in three concentric layers of tissues: the outer protoderm, the inner mass of ground tissue, and the centrally located vascular bundles. This pattern is initiated within the first eight cel...

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“…Unfortunately, other molecular markers that would reveal polarity at an earlier stage of embryogenesis are not currently available. Nevertheless, the evidence presented here strongly suggests that the apical-basal polarity of the embryo is not fixed before fertilization, although the Arabidopsis egg cell is morphologically polar:In other flowering plants, the egg cell appears apolar or polarity is reversed upon fertilization (Johri, 1984). Thus, apical-basal polarity of flowering plant embryos appears to be established within the zygote and fixed by its first division.…”

mentioning

confidence: 66%

“…In other flowering plants, the egg cell appears apolar or polarity is reversed upon fertilization (Johri, 1984). Thus, apical-basal polarity of flowering plant embryos appears to be established within the zygote and fixed by its first division.…”

Section: Embryos: Lmplications For Pattern Formation In the Arabidopsmentioning

confidence: 99%

Pattern Formation in the Arabidopsis Embryo Revealed by Position-Specific Lipid Transfer Protein Gene Expression

Vroemen¹,

Langeveld²,

Mayer³

et al. 1996

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During Arabidopsis embryogenesis, the zygote divides asymmetrically in the future apical-basal axis; however, a radial axis is initiated only within the eight-celled embryo. Mutations in the GNOM, KNOLLE, and KEULE genes affect these processes: gnom zygotes tend to divide symmetrically; knolle embryos lack oriented cell divisions that initiate protoderm formation; and in keule embryos, an outer cell layer is present that consists of abnormally enlarged cells from early development. Pattern formation along the two axes is reflected by the position-specific expression of the Arabidopsis lipid transfer protein (AtLTPT) gene. In wild-type embryos, the AtLTPl gene is expressed in the protoderm and initially in all protodermal cells; later, AtLTPí expression is confined to the cotyledons and the upper end of the hypocotyl. Analysis of AtLTPT expression in gnom, knolle, and keule embryos showed that gnom embryos also can have no or reversed apical-basal polarity, whereas radial polarity is unaffected. knolle embryos initially lack but eventually form a radial pattern, and keule embryos are affected in protoderm cell morphology rather than in the establishment of the radial pattern. INTRODUCTIONIn flowering plants, the primary body plan of the seedling is laid down during embryogenesis (Steeves and Sussex, 1989). This body plan has been described as the superimposition of an apical-basal and a radial pattern . The apical-basal pattern visible in the seedling consists of distinct elements: two cotyledons, shoot meristem, hypocotyl, and root, including the root meristem. In Arabidopsis, the apical-basal polarity is already evident in the zygote, which elongates approximately threefold in the apical direction. An asymmetric division then generates a small apical cell from which all pattern elements are derived, except for part of the root, that is, the columella root cap and the quiescent center (Scheres et al., 1994), and the suspensor, which are derived from the larger basal cell. Mutations resulting in a deletion of regions of the apical-basal pattern include gurke, fackel, monopteros, and gnom (Mayer et al., , 1993 Berleth and Jürgens, 1993) and rootless, shoot meristemless, and topless (Barton and Poethig, 1993).In gnom embryos (Mayer et al., , 1993Busch et al., 1996), also called emb30 embryos (Shevell et al., 1994;Franzmann et al., 1995), the zygote tends to divide symmetrically, producing an enlarged apical cell at the expense of the basal cell. gnom embryos have no root meristem and reduced orno cotyledons, and most gnom seedlings are cone shaped, 'To whom correspondence should be addressed.retaining apical-basal polarity, although the pattern is severely compromised. Some gnom seedlings, however, are ball shaped, displaying no morphologically apparent apical-basal polarity (Mayer et al., 1993). The radial pattern is arranged in three concentric layers of tissues: the outer protoderm, the inner mass of ground tissue, and the centrally located vascular bundles. This pattern is initiated within the first eight cel...

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“…Postchalazals bundles were also observed in Platonia insignis (Moronobeoideae) by Mourão & Beltrati (1995a). According to Johri & Ambegaokar (1984) the vascular supply of the ovule is variable, being quite developed in primitive families. The fruit and seed development in Mammea americana resembles that one presents in Calophyllum inophyllum (Calophlylloideae), described by Corner (1976).…”

Section: Discussionmentioning

confidence: 99%

Morphology and anatomy of developing fruits and seeds of Mammea americana L. (Clusiaceae)

Mourão

¹

,

Beltrati

²

2000

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Morphological, structural and developmental features of fruits and seeds of Mammea americana L. are here studied, with the purpose to give a proper classification of their fruit and embryo type and to contribute to future taxonomical and ecological studies. The fruit is a berry and the "rind" consists of the exocarp, represented by a periderm with lenticels, and by the parenchymatic mesocarp, with branched secretory ducts and vascular bundles. The edible pulpy is formed by the endocarp, destituted of secretory ducts, and derived from the activity of a ventral meristem, which emerges early in the fruit development. The inner endocarp cell layers undergo a radial elongation and become firmly attached to the testal outer layers. At maturation the endocarp may be released from the rest of the pericarp. The ovules are unitegmic and they turn into unitegmic and exalbuminous seeds. The multiseriate testa consists of thick-walled cells and sclerenchymatous fibers. This last features have carried out to a wrong interpretation that the fruit of this species is a drupe. The embryo is pseudo-conferruminate, with two massive foodstoring cotyledons, rich in starch, firmly attached.Key words: Clusiaceae, fruit, seed, Mammea, anatomy. RESUMO Morfologia e anatomia dos frutos e sementes em desenvolvimento de Mammea americana L. (Clusiaceae)Descreveu-se, detalhadamente, a morfologia e a anatomia dos frutos e sementes, em desenvolvimento, de Mammea americana L., de modo a identificar corretamente o tipo de fruto e de embrião desta espé-cie, bem como contribuir com futuros estudos taxonômicos e ecológicos do grupo. O fruto desta espécie é uma baga, cuja "casca" é constituída pelo exocarpo, representado por uma periderme com lenticelas, e pelo mesocarpo, percorrido longitudinalmente por dutos secretores e feixes vasculares. O endocarpo, desprovido de dutos, origina-se da atividade de um meristema ventral e da epiderme interna do ovário. Suas células posteriormente se alongam em sentido radial, transformando-se na polpa amarelada, comestível, rica em açúcares e fibras, aderida à testa fibrosa. Os óvulos anátropos, unitegumentados originam sementes unitegumentadas e exalbuminosas. A testa multisseriada, constituída por parênquima de parede espessada e fibras esclerenquimáticas alongadas acompanhando os feixes vasculares muito ramificados, confere à semente o aspecto fibroso externo. Esta característica levou à interpretação errônea de que o fruto desta espécie seria uma drupa. O embrião é pseudo-conferruminado e constituído pelos cotilédones carnosos, fusionados.Palavras-chave: Clusiaceae, fruto, semente, Mammea, anatomia.Rev. Brasil. Biol., 60(4): 701-711 702 MOURÃO, K. S. M. and BELTRATI, C. M.

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Embryology: Then and Now

Cited by 22 publications

References 56 publications

Pattern Formation in the Arabidopsis Embryo Revealed by Position-Specific Lipid Transfer Protein Gene Expression.

Pattern Formation in the Arabidopsis Embryo Revealed by Position-Specific Lipid Transfer Protein Gene Expression.

Pattern Formation in the Arabidopsis Embryo Revealed by Position-Specific Lipid Transfer Protein Gene Expression

Morphology and anatomy of developing fruits and seeds of Mammea americana L. (Clusiaceae)

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