Developmental and Structural Section
Long, Joel A. , Renzaglia, Karen S. .
Sporogenesis in the moss, Takakia ceratophylla.
Takakia is an enigmatic moss that is genetically and structurally divergent from other taxa. Although similar to true mosses in seta elongated through cell division, the sporophyte of Takakia is extraordinary in the mode of dehiscence through a single, spiraled, longitudinal slit. To fill in gaps in knowledge of the structural biology of this phylogenetically significant moss, we conducted an anatomical and ultrastructural study of the complete process of sporogenesis. In unexpanded capsules, archesporial cells are isodiametric (diameter 12 μm), monoplastidic and highly vacuolated. When the seta reaches its maximum length, the capsule expands through rapid cell divisions, followed by cell expansion. Spore mother cells (SMCs) are first visible as square cells with thin cell walls. Golgi vesicles deposit wall material around SMC, "shrinking" the protoplasm away from the original wall. SMCs deposit a thin new wall and expand to a diameter of approximately 35 μm. In preparation for meiosis, the lone plastid divides twice, and the resulting four plastids migrate to tetrahedral poles. Nascent tetrads, are approximately 55 μm in diameter and are enclosed in SMC walls, which persist until spore maturation. Spore wall development proceeds centripetally and begins with production of exine through deposition of tripartite lamellae and sporopollenin. The intine is an electron-lucent fibrillar network that borders the plasmalemma. The trilete mark is differentiated into an aperture in which the intine is greatly expanded. In the final stages of sporogenesis, a dense perine is deposited on the spore surface. The mode of development and structure of mature spore wall shows little similarity with eperistomate mosses, while the existence of tripartite lamellae and the structure of the aperture are features that Takakia shares with true mosses.
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1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
spore wall development.
Presentation Type: Oral Paper
Location: Salon A - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 10:45 AM