Meeting Abstract

5.5  Monday, Jan. 4  Examining the gametophytic calyptra and its role in moss sporophyte development using the cord moss (Funaria hygrometrica). BUDKE, J.M.; University of Connecticut

In bryophytes (mosses, liverworts and hornworts) the diploid sporophyte is small, unbranched, and physically attached to the maternal haploid gametophyte. One of the major maternal influences in moss plants is a cap of gametophyte tissue (the calyptra) that covers the sporophyte’s apex during early developmental stages. Previous studies indicate that the calyptra functions mechanically to influence sporophyte development and is necessary for spore formation. Sporophytes without their calyptra wilt at the apex; they survive only when placed in a high humidity chamber. These observations stimulated the hypothesis that the maternally derived calyptra functions as a waterproof cap, preventing desiccation of the developing sporophyte’s apex. In plants the cuticle, an external layer of lipids and waxes, maintains internal hydration. To explore this hypothesis, I am using scanning and transmission electron microscopy to examine cuticle morphology and development of both the calyptra and sporophyte in the moss Funaria hygrometrica. Results for this species indicate that the calyptra’s cuticle is thicker and more complex than other gametophyte tissues; the cuticle is also present on the calyptra throughout sporophyte development. These observations support the calyptra as a specialized maternal gametophyte structure and provide a mechanism by which the calyptra prevents harmful water loss during critical sporophyte developmental stages. Sporophyte development is directly related to reproductive output and thus evolutionary fitness in mosses. The material care provided by the calyptra and its cuticle may have been a critical innovation for the evolutionary success of the ~12,500 moss species worldwide. This research is supported by a 2009 AMS Student Research Fellowship.