Developmental and Structural Section
Romanova, Marina , Jernstedt, Judy .
Do patterns of cell division matter? Inferences from shoot morphogenesis in Ceratopteris richardii.
One contemporary view of shoot apical meristem (SAM) structure and function emphasizes the ubiquitous nature of zonation patterns in SAMs of land plant sporophytes and de-emphasizes cell division-based differences. We show, however, that division patterns of and related to the single apical cell (AC) of the Ceratopteris richardii SAM are correlated with many specific characters in organo- and histogenesis. In both duplex (angiosperm and gnetophyte) and simplex (Lycopodium and conifer) SAMs, populations of central zone (CZ) and peripheral zone (PZ) cells are maintained through proliferative divisions. CZ and PZ cells in angiosperm SAMs constitute more or less fixed units or domains, with generally indistinguishable cells entering and departing. In the C. richardii monoplex SAM, all divisions within immediate and later AC segments are unequal and formative. Only the AC persists as an undifferentiated cell, while the identities and fates of all derivates change with each AC division. The clonal relationship of surface cells (L1) with their subsurface "sisters" in fern SAMs differs from that in stratified duplex SAMs. Other differences include the mechanism of leaf origin; in C. richardii the leaf apical cell (LAC) arises through a precise sequence of formative divisions in each shoot AC segment. Since each AC segment in C. richardii is destined to become organogenic, there is no need for re-specifying cell fate as happens during leaf founder cell recruitment in the PZ of angiosperms. The ultimate formation of both leaf and root(s) in every AC segment, interconnected by vascular tissues, and the merophyte's gradual symplasmic isolation due to inability to form secondary plasmodesmata, makes morphogenesis in each segment largely autonomous. However, in C. richardii histogenesis, positional information dominates over information inherited through lineage.
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1 - University of California, Davis, Plant Sciences, One Shields Avenue, Davis, California, 95616-8780, USA
cell lineage map.
Presentation Type: Poster
Location: Salon C, D & E - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 12:30 PM