Origin, Structure, and Interpretation of the Thallus in<i>Hydrobryopsis sessilis</i>(Podostemaceae)

Sehgal, Amit; Sethi, Minakshi; Ram, H. Y. Mohan

doi:10.1086/342082

Cited by 33 publications

(30 citation statements)

References 32 publications

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“…In most dicots, e.g., Arabidopsis, the hypophyseal cell gives rise to four QC precursor cells by the first transverse and subsequent two longitudinal divisions during transition from the globular to heart stage (Johri et al 1992;Mansfield and Briarty 1991;J•ü•rgens and Mayer 1994). Therefore, the putative QC initials in T. Sehgal et al 2002;Suzuki et al 2002). In our preliminary observations, similar to the hypophysis development of Z. lichenoides and H. japonicum, longitudinal divisions of the hypophyseal cells were repeated during the early embryogenesis of Weddellina squamulosa, Weddellinoideae, whose seedling is rootless (N. Katayama, unpubl.…”

Section: Loss Of the Embryonic Root Meristemmentioning

confidence: 80%

“…In contrast to such variations in the seedling shoot apex, a primary root and an embryonic root meristem do not form at the basal tip of the hypocotyl in the Podostemoideae that have been examined (Fig. 1, C and D;Warming 1882;Willis 1902;Philbrick 1984;Mohan Ram and Sehgal 1997;Jager-Zürn 2000;Uniyal and Mohan Ram 2001;Sehgal et al 2002;Suzuki et al 2002). Molecular phylogenetic studies show that the subfamily Tristichoideae is basally diverged in the family, followed by the monotypic Weddellinoideae and the most diversified Podostemoideae (Cook 1996;Cook and Rutishauser 2007;Kita and Kato 2001).…”

Section: Introductionmentioning

confidence: 92%

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Comparative anatomy of embryogenesis in three species of Podostemaceae and evolution of the loss of embryonic shoot and root meristems

Katayama

Kato

Nishiuchi

et al. 2011

Evolution &Amp; Development

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During embryogenesis in angiosperms, the embryonic shoot and root meristems are created at opposite poles of the embryo, establishing the vertical body plan. However, the aquatic eudicot family Podostemaceae exhibits an unusual horizontal body plan, which is attributed to the loss of embryonic shoot and root meristems. To infer the embryogenetic changes responsible for the loss of these meristems, we examined the embryogenesis of three podostemads with different meristem characters, i.e., Terniopsis brevis with distinct shoot and root meristems, Zeylanidium lichenoides with reduced shoot and no root meristems, and Hydrobryum japonicum with no shoot and no root meristems. In T. brevis, as in other eudicots, the putative organizing center (OC) and L1 layer (= the epidermal cell layer) arose to generate a distinct shoot meristem initial, and the hypophysis formed the putative quiescent center (QC) of a root meristem. Z. lichenoides had a morphologically unrecognizable shoot meristem, because a distinct L1 layer did not develop, whereas the putative OC precursor arose normally. In H. japonicum, the vertical divisions of the apical cells of 8-cell embryo prevented putative OC initiation. In Z. lichenoides and H. japonicum, the putative QC failed to initiate because the hypophysis repeated longitudinal divisions during early embryogenesis. Based on their phylogenetic relationships, we infer that the conventional embryonic shoot meristem was lost in Podostemaceae via two steps, i.e., the loss of a distinct L1 layer and the loss of the OC, whereas the loss of the embryonic root meristem occurred once by misspecification of the hypophysis.

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Section: Loss Of the Embryonic Root Meristemmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 92%

Comparative anatomy of embryogenesis in three species of Podostemaceae and evolution of the loss of embryonic shoot and root meristems

Katayama

Kato

Nishiuchi

et al. 2011

Evolution &Amp; Development

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“…The basic body plan of most of the podostemads is thalloid, deviating considerably from the classical root-shoot model typical of angiosperms, and hence is a structural novelty. Plants of this family are characterized by marked structural and developmental reductionism (Willis 1902a, b;Mohan Ram and Sehgal 1992, 2001, 2007Rutishauser 1997) and several unique embryological features, such as absence of an identifiable shoot apical meristem and root apical meristem (in the mature embryo), absences of antipodals, triple fusion and endosperm; and presence of a four-nucleate mature megagametophyte, pseudo-megagametophyte, single fertilization and suspensor haustoria (Razi 1949;Mukkada 1962;Chopra and Mukkada 1966;Kapil 1970;Battaglia 1971;Mukkada and Chopra 1973;Nagendran 1975;Sehgal et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Occurrence of unique three-celled megagametophyte and single fertilization in an aquatic angiosperm-Dalzellia zeylanica (Podostemaceae-Tristichoideae)

et al. 2010

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Angiosperms are characterized by the occurrence of double fertilization. However, Podostemaceae is considered an exception with the presence of only single fertilization (syngamy) though two male gametes are formed conventionally. To determine the cause for the failure of double fertilization in Dalzellia zeylanica (Gardn.) Wight, we closely tracked the movement of the male gametes from the time of pollen tube initiation to the time of entry into the megagametophyte to affect fertilization. We report for the first time, the presence of a novel type of three-nucleate/three-celled mature megagametophyte consisting of two synergids and an egg cell in D. zeylanica. Therefore, of the two male gametes formed in this plant, one fuses with the egg cell resulting in syngamy, whereas the other male gamete eventually degenerates due to the absence of its partner i.e. single polar nucleus of the central cell that degenerates prior to the entry of the pollen tube into the synergid. The present work not only highlights the highly reduced nature of megagametophyte but also the occurrence of single fertilization resulting in sperm selection in D. zeylanica.

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“…, 2006), modified shoot (Rutishauser & Grubert, 1994; Philbrick & Novelo, 1995; Jäger‐Zürn, 1997; Rutishauser, 1997) or a combined leaf–stem structure (Willis, 1902b). In a previous paper (Sehgal, Sethi & Mohan Ram, 2002), we reported the origin, structure and organ identity of the dorsiventral thallus in H. sessilis . We interpreted the thalloid plant body as a flattened stem.…”

Section: Introductionmentioning

confidence: 99%

Development of the floral shoot and pre-anthesis cleistogamy inHydrobryopsis sessilis(Podostemaceae)

Sehgal

Sethi

Ram

2009

Botanical Journal of the Linnean Society

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The reproductive biology of Hydrobryopsis sessilis (Podostemaceae, subfamily Podostemoideae), a reduced, threatened, aquatic angiosperm endemic to the Western Ghats of India, was examined. This is the first report on the transition from the vegetative to the reproductive phase in this plant, describing floral ontogeny, pollination and the breeding system. The cytohistological zonation of the apical meristem of the reproductive thallus is identical to that of the apical meristem of the vegetative thallus. The floral shoots do not replace vegetative shoots (i.e. the vegetative shoots never bear flowers), but form at new sites at the tip of the flattened plant body. Each floral shoot meristem is tiny, deep-seated and concave and arises endogenously following lysigeny. The floral shoot meristem gives rise to four to six bracts in a distichous manner. The development of spathe, stamens and carpels is described. The ab initio dorsiventrality of the carpels and the occurrence of endothelium in the ovules are reported. The mature stigmas and anthers lie close to each other. The pollen germinates within undehisced anthers and the pollen tubes enter the stigmas in the unopened floral bud, leading to pre-anthesis, complete, constitutional cleistogamy under water. The seed set is 63.2%. A significant finding is the penetration of several pollen tubes into the filaments of stamens in 16% of the flower buds, indicating a trend towards cryptic self-fertilization. The Indian Podostemoideae appear to show a shift from xenogamy or geitonogamy or autogamy in a chasmogamous flower to complete autogamy in a cleistogamous flower. The floral modifications leading to cleistogamy in H. sessilis have been identified.

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Origin, Structure, and Interpretation of the Thallus inHydrobryopsis sessilis(Podostemaceae)

Cited by 33 publications

References 32 publications

Comparative anatomy of embryogenesis in three species of Podostemaceae and evolution of the loss of embryonic shoot and root meristems

Comparative anatomy of embryogenesis in three species of Podostemaceae and evolution of the loss of embryonic shoot and root meristems

Occurrence of unique three-celled megagametophyte and single fertilization in an aquatic angiosperm-Dalzellia zeylanica (Podostemaceae-Tristichoideae)

Development of the floral shoot and pre-anthesis cleistogamy inHydrobryopsis sessilis(Podostemaceae)

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