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J Plant Res (2012) 125:197206 DOI 10.1007/s10265-011-0425-y
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Evolution of apolar sporocytes in marchantialean liverworts: implications from molecular phylogeny
Masaki Shimamura Misao Itouga
Hiromi Tsubota
Received: 19 January 2011 / Accepted: 3 April 2011 / Published online: 5 May 2011 The Botanical Society of Japan and Springer 2011
Abstract In meiosis of basal land plants, meiotic division planes are typically predicted by quadri-lobing of the cytoplasm and/or quadri-partitioning of plastids prior to nuclear divisions. However, sporocytes of several march-antialean liverworts display no indication of premeiotic establishment of quadripolarity, as is observed in owering plants. In these cases, the shape of sporocytes remains spherical or elliptical and numerous plastids are distributed randomly in the cytoplasm during meiosis. Through a survey of sporocyte morphology in marchantialean liver-worts, we newly report the occurrence of apolar sporocytes in Sauteria japonica and Athalamia nana (Cleveaceae; Marchantiales). Molecular phylogenetic analyses revealed that the quadri-lobing of cytoplasm and quadri-partitioning of plastids were lost independently several times during the evolution of marchantialean liverworts. In addition, our phylogenetic analyses indicate that the simplied sporophytes of several marchantialean liverworts are not a primitive condition but rather represent the result of
reductive evolution. The loss of the quadripolarity of sporocytes appears to correlate with the evolutionary trend of the sporophyte towards reductions. Through the evolution of the simplied sporophytes, suppression of mitotic divisions of sporogenous cells might had caused not only the modication of sporophyte ontogeny but also the drastic cytological change of sporocyte.
Keywords Bryophytes Sporogenesis Sporophyte
Phylogeny Marchantialean liverworts
Introduction
Spore morphology and sporogenesis in bryophytes have proven to be feature of remarkable taxonomic relevance (Neidhart 1979; Brown and Lemmon 1990a; Renzaglia et al. 2007). Although taxonomic studies have tended to concentrate on the morphology of mature spores, considerable variations in the morphology of sporocytes (spore mother cells) have also been reported. For example, Schuster (1984) noted that unlobed sporocytes of march-antialean liverworts are distinct from deeply-lobed sporocytes of jungermannialean liverworts. In meiosis of jungermannialean liverworts, future cytokinetic division planes are determined before nuclear division by the cytoplasmic lobing in prophase-I (Brown and Lemmon, 2006). Although mosses and hornworts also have four-lobed sporocytes, variability exists in the degree of lobing (Brown and Lemmon 1987, 1990a, b). In contrast, a number of marchantialean liverworts...