Department of Biological Science, Graduate School of Science, Hiroshima University, Kagami-yama, Higashi Hiroshima, Hiroshima 739-8526, Japan.
J Plant Res. 2012 Mar;125(2):197-206. doi: 10.1007/s10265-011-0425-y. Epub 2011 May 5.
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 marchantialean liverworts display no indication of premeiotic establishment of quadripolarity, as is observed in flowering 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 liverworts, 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 simplified 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 simplified sporophytes, suppression of mitotic divisions of sporogenous cells might had caused not only the modification of sporophyte ontogeny but also the drastic cytological change of sporocyte.
在基域植物的减数分裂中，在核分裂之前，细胞质的四分叶和/或质体的四分体通常可预测减数分裂平面。然而，几个卷柏目的苔类植物的孢子细胞没有表现出减数分裂前建立四极性的迹象，这在开花植物中是观察到的。在这些情况下，孢子细胞的形状仍然是球形或椭圆形，并且在减数分裂期间许多质体随机分布在细胞质中。通过对卷柏目的苔类植物的孢子细胞形态的调查，我们新报道了日本沙苔（Cleveaceae；卷柏目）和 Nana 阿塔利亚苔（Athalamia nana）中出现无极性孢子细胞。分子系统发育分析表明，在卷柏目的苔类植物的进化过程中，细胞质的四分叶和质体的四分体独立地多次丢失。此外，我们的系统发育分析表明，几个卷柏目的苔类植物简化的孢子体不是原始条件，而是代表了简化进化的结果。孢子细胞的四极性的丧失似乎与孢子体向简化的进化趋势相关。通过简化的孢子体的进化，对孢子形成细胞有丝分裂的抑制不仅可能引起孢子体发生的改变，而且可能引起孢子细胞的剧烈细胞学变化。
