Developmental and Structural Section
Friedman, William , Bachelier, Julien .
The search for a proto-endosperm: are the minute endosperms of Nymphaeales a vestige of the first endosperms in flowering plants?
For over a century, the key intermediate steps involved in the transition from an embryo-nourishing female gametophyte (as in gymnosperms) to the embryo-nourishing triploid endosperm of most flowering plants have remained obscure. With the recent discovery of diploid endosperms in ancient lineages of angiosperms (Nymphaeales and Austrobaileyales), one of the transitional states appears to have been revealed: the first flowering plants were likely to have had a diploid endosperm, with a subsequent transition to a triploid endosperm in the common ancestor of monocots, eudicots, and magnoliids. Irrespective of ploidy, it has long been assumed that the common ancestor of extant angiosperms formed a full-fledged nutrient-storing and embryo-nourishing endosperm. However, our survey of the embryological literature finds that members of many of the most ancient lineages of angiosperms (Nymphaeales, Saururaceae, Piperaceae, Hydnoraceae, possibly Trimeniaceae and Ceratophyllaceae) form an embryo-nourishing perisperm along with a minute endosperm. In Nymphaeales, the perisperm is paired with a diploid endosperm, while in others groups, the perisperm is paired with a triploid or even higher ploidy endosperm. Interestingly,when the presence of a perisperm is mapped onto a current phylogeny of the major lineages of flowering plants, a noteworthy insight is obtained: perisperm with a minute endosperm either evolved several times during the early diversification of angiosperms, or was the plesiomorphic condition for angiosperms as a whole. Accordingly, perisperm-based embryo-nourishing behavior, as found in the Nymphaeales, could have preceded the evolution of a full-fledged endosperm as the primary nutrient storage tissue within a flowering plant seed. As such, the minute (diploid) endosperm of Nymphaeales might represent a "proto-endosperm" Ěthat has yet to have evolved the functions of nutrient acquisition, storage and mobilization. We will examine the functional and evolutionary implications of the presence of a minute endosperm and copious perisperm in Nymphaeales within the context of the alternative hypotheses that perisperm in water lilies is apomorphic or is a manifestation of the plesiomorphic condition for all angiosperms.
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1 - Arnold Arboretum of Harvard, 1300 Centre St, Boston, MA, 02131, USA
nutrient transfer tissue.
Presentation Type: Oral Paper:Papers for Sections
Location: Union D/Hyatt
Date: Monday, July 9th, 2012
Time: 3:30 PM