Developmental and Structural Section
Povilus , Rebecca , Losada , Juan M , Friedman, William E .
Pre-fertilization reproductive development and floral biology in the remarkable water lily, Nymphaea thermarum.
As an annual, diminutive water lily, Nymphaea thermarum possesses a unique combination of characters that makes it a promising system for experimental studies – something that is rare among basal angiosperm lineages. Unfortunately, it has also recently become extinct in the wild, with germplasm maintained in only a few botanical gardens worldwide. As a result, little is known about its reproductive biology. We use a combination of microscopy approaches (brightfield, epifluoresence, confocal) to capture key stages of pre-fertilization floral and reproductive biology in N. thermarum. Hermaphroditic members of Nymphaeales are generally self-compatible but protogynous, with the female phase occurring on the first day of anthesis and the male phase expressed over the next 1-5 days. In N. thermarum, however, pollen is shed as early as one day before anthesis. Precocious anther dehiscence may be more common in tropical members of Nymphaea than generally thought, and suggests that the clade has an unappreciated capacity for variation in floral biology. On the other hand, female gametophyte development in N. thermarum is typical for Nymphaeales. The female gametophyte is of the Nuphar/Schisandra type (monosporic and four-celled at maturity), and comprises only a small portion of ovule volume. The majority of the mature ovule is instead occupied by nucellus. The micropylar nucellar epidermis develops conspicuous cell wall ingrowths, as has been noted in several other members of Nymphaea as sclerification. However, histochemical investigation of N. thermarum reveals that these ingrowths are due rather to discrete layering of cellulose and callose, and are therefore similar to transfer cell cytology. The composition of the cell wall ingrowths changes dramatically in response to pollen tube penetration and fertilization. Finally, pollen tube entry and sperm cell discharge demonstrate double fertilization, yielding a zygote and primary endosperm cell. Besides providing perspective on evolution of reproductive characters within Nymphaeales, understanding the reproductive biology and development of N. thermarum is essential for conserving what genetic diversity still exists, and for facilitating the use of this species as an experimental system.
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1 - Arnold Arboretum of Harvard University, Organismic and Evolutionary Biology, 1300 Centre Street, Boston, Massachusetts, 02131, United States
2 - Arnold Arboretum Of Harvard University, Organismic And Evolutionary Biology, 1300 Centre Street, Boston, MA, 02131, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Pines North/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 2:30 PM
Candidate for Awards:Katherine Esau Award