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Floral structure and development in Rafflesiaceae with emphasis on their exceptional gynoecia


Nikolov, Lachezar A; Staedler, Yannick M; Manickam, Sugumaran; Schönenberger, Jürg; Endress, Peter K; Kramer, Elena M; Davis, Charles C (2014). Floral structure and development in Rafflesiaceae with emphasis on their exceptional gynoecia. American Journal of Botany, 101(2):225-243.

Abstract

PREMISE OF THE STUDY:
The holoparasitic plant family Rafflesiaceae include the world's largest flowers. Despite their iconic status, relatively little is known about the morphology and development of their flowers. A recent study clarified the organization of the outer (sterile) floral organs, surprisingly revealing that their distinctive floral chambers arose via different developmental pathways in the two major genera of the family. Here, we expand that research to investigate the structure and development of the reproductive organs of Rafflesiaceae.
METHODS:
Serial sectioning, scanning electron microscopy, and x-ray tomography of floral buds were employed to reconstruct the structure and development of all three Rafflesiaceae genera.
KEY RESULTS:
Unlike most angiosperms, which form their shoot apex from the primary morphological surface, the shoot apex of Rafflesiaceae instead forms secondarily via internal cell separation (schizogeny) along the distal boundary of the host-parasite interface. Similarly, the radially directed ovarial clefts of the gynoecium forms via schizogeny within solid tissue, and no carpels are initiated from the floral apex.
CONCLUSIONS:
The development of the shoot apex and gynoecium of Rafflesiaceae are highly unusual. Although secondary formation of the morphological surface from the shoot apex has been documented in other plant groups, secondary derivation of the inner gynoecium surface is otherwise unknown. Both features are likely synapomorphies of Rafflesiaceae. The secondary derivation of the shoot apex may protect the developing floral shoot as it emerges from within dense host tissue. The secondary formation of the ovarial clefts may generate the extensive placental area necessary to produce hundreds of thousands of ovules.

Abstract

PREMISE OF THE STUDY:
The holoparasitic plant family Rafflesiaceae include the world's largest flowers. Despite their iconic status, relatively little is known about the morphology and development of their flowers. A recent study clarified the organization of the outer (sterile) floral organs, surprisingly revealing that their distinctive floral chambers arose via different developmental pathways in the two major genera of the family. Here, we expand that research to investigate the structure and development of the reproductive organs of Rafflesiaceae.
METHODS:
Serial sectioning, scanning electron microscopy, and x-ray tomography of floral buds were employed to reconstruct the structure and development of all three Rafflesiaceae genera.
KEY RESULTS:
Unlike most angiosperms, which form their shoot apex from the primary morphological surface, the shoot apex of Rafflesiaceae instead forms secondarily via internal cell separation (schizogeny) along the distal boundary of the host-parasite interface. Similarly, the radially directed ovarial clefts of the gynoecium forms via schizogeny within solid tissue, and no carpels are initiated from the floral apex.
CONCLUSIONS:
The development of the shoot apex and gynoecium of Rafflesiaceae are highly unusual. Although secondary formation of the morphological surface from the shoot apex has been documented in other plant groups, secondary derivation of the inner gynoecium surface is otherwise unknown. Both features are likely synapomorphies of Rafflesiaceae. The secondary derivation of the shoot apex may protect the developing floral shoot as it emerges from within dense host tissue. The secondary formation of the ovarial clefts may generate the extensive placental area necessary to produce hundreds of thousands of ovules.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Systematic and Evolutionary Botany
Dewey Decimal Classification:580 Plants (Botany)
Language:English
Date:2014
Deposited On:07 Mar 2014 14:50
Last Modified:08 Dec 2017 04:19
Publisher:Botanical Society of America
ISSN:0002-9122
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.3732/ajb.1400009
PubMed ID:24509798

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