Developmental and Structural Section
Budke, Jessica M. , Goffinet, Bernard , Jones, Cynthia S. .
Beneath the Calyptra’s Veil: Exploring Cuticle Anatomy during Moss Sporophyte Development.
In mosses and other bryophytes, the sporophyte is small, unbranched, and physically attached to the maternal gametophyte. This attachment allows transfer of nutrients from the maternal plant to the developing sporophyte and is considered a critical innovation for embryophyte evolution. Unique to mosses, a cap of maternal gametophyte tissue, called the calyptra, covers the sporophyte’s apex during early development. Experimental studies have shown that the calyptra is necessary for sporangium formation and ultimately sporogenesis. Replacing a living calyptra with an extracted/dead calyptra can result in normal sporophyte development, indicating a mechanical role. High humidity chambers are used in calyptra removal experiments, otherwise the sporophyte wilts. This suggests that another role of the maternal calyptra is to prevent desiccation of the developing sporophyte. Support for this hypothesis would predict 1) the presence of a cuticle-like layer on the calyptra to prevent water loss and 2) the lack of a similar layer on the sporophyte apex at early developmental stages.
Scanning and transmission electron microscopy were used to examine cuticle morphology, anatomy and development on both calyptrae and sporophytes at nine developmental stages. Results from Funaria hygrometrica indicate that a cuticle is not only present in the calyptra, but that it is thicker and more complex than other gametophyte organs. The mature cuticle is present on the calyptra at early stages and persists throughout sporophyte development, while the cuticle of the sporophyte apex remains immature until later developmental stages. These observations support the calyptra as a specialized maternal structure that may prevent harmful water loss during sensitive stages of sporophyte development. Because sporophyte development is directly related to reproductive output and thus fitness in mosses, we propose that the calyptra and its cuticle provide a unique mode of maternal care, which may have been a critical innovation for the early evolutionary success of mosses on land.
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1 - University of Connecticut, Ecology & Evolutionary Biology, 75 North Eagleville Road, U-3043, Storrs, Connecticut, 06269-3043, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 555B/Convention Center
Date: Wednesday, August 4th, 2010
Time: 10:00 AM