Abstract Detail

Bryological and Lichenological Section/ABLS

Johnson, Eric E [1], Rogers, Cassandra E. [1].

Spore wall development in Sphaerocarpos texanus.

Sphaerocarpos is one of the few bryophytes in which spores are dispersed in tetrads. Because each tetrad includes two male and two female spores, this type of dispersal facilitates the development of populations with both sexes. Previous reports of spore morphogenesis in the Sphaerocarpales, conducted primarily at the light microscope level, are conflicting and incomplete. In this study we provide a detailed description of the entire process of sporogenesis in Sphaerocarpos texanus using light, fluorescence and electron microscopy. In the young capsule, spore mother cells are first distinguished from starch-filled nurse cells by an abundance of oil. Prior to meiosis, the sporocyte becomes rounded and remains unlobed. Following meiosis, intersporal walls separate the four spores in each tetrad and a callosic primexine is deposited around the circumference of each spore. On the distal surface of the spore, the outer exine consists of approximately five solitary, widely-separated, tripartite lamellae that are laid down within the template of the primexine. On the outside of the tetrad, the lamellae form a bridge between adjacent spores. This connection is reinforced by sporopollenin deposition, ensuring that spores are permanently united in tetrads. Callose progressively disappears as sporopollenin is deposited on the lamellae, a process that is delayed on the proximal spore surface. An inner exine, comprising a band of 12-14 tightly compacted lamellae, forms around each spore, followed by a loosely fibrillar intine. Upon dispersal, and if conditions are optimal, the four spores of each tetrad germinate through their distal surfaces in a region of the exine where the lamellae are less compressed.

1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA

Keywords:
callose
liverwort
spore tetrad.

Presentation Type: Paper
Session: 23-5
Location: Ballroom 3 (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 4:15 PM
Abstract ID:694