O'Kelly C J, Floyd G L
Biosystems. 1983;16(3-4):227-51. doi: 10.1016/0303-2647(83)90007-2.
The absolute orientation of the flagellar apparatus in green algal motile cells is a feature of considerable value in studies of green algal systematics and phylogeny. The absolute orientation patterns found in those algae for which this feature is known or can be deduced are reviewed. Counterclockwise absolute orientation occurs in all classes except the Chlorophyceae and is considered primitive, while the clockwise absolute orientation present in most members of the Chlorophyceae is the result of progressive clockwise rotation of components during evolution. Extant intermediates documenting this rotation include Hafniomonas vegetative cells, which show counterclockwise absolute orientation, and Chaetopeltis quadriflagellate zoospores, in which the flagellar apparatus is strictly cruciate except for a slight clockwise offset of the microtubular rootlets. The V-shaped arrangement of the basal bodies in the flagellar apparatus, as well as the presence of proximal sheaths and of two layers of scales on the cell body, further identifies the Chaetopeltis zoospore as a primitive cell type within the Chlorophyceae . Trends towards the exsertion of basal bodies from a flagellar pit, either apically or laterally, the elimination of quadriflagellate cells, and, in the Chlorophyceae , an increasing amount of basal body offset, indicate advancement within the classes. Absolute orientation is conserved during flagellar apparatus replication and development. Events after flagellar apparatus division in the algae studied may be subdivided into component assembly, which is universal and preserves phylogenetically-useful features, and component reorientation, which occurs in relatively few green algae and adapts the flagellar apparatus to specialized functions. From these flagellar apparatus orientation studies, a major reevaluation of evolution within the Chlorophyceae is proposed, with weakly- thalloid algae possessing desmoschisis (e.g. Chaetopeltis ) considered primitive, and most other types, including the Volvocales , considered more advanced. The evolution of wall formation does not preclude the formation of scales in primitive chlorophycean genera. In addition, one or more previously undescribed major lineages may exist within the green algae, including one, the Pleurastrum lineage, whose members possess dorsiventrally -flattened motile cells, counterclockwise absolute orientation of the flagellar apparatus, and a phycoplast at cytokinesis. The Chlorophyceae , the Ulvophyceae , and the Pleurastrum lineage are considered to have a common ancestor that resembled the modern genus Pyramimonas , while the Charophyceae is thought to be of more ancient derivation. Th
绿藻游动细胞中鞭毛器的绝对取向在绿藻系统学和系统发育研究中具有重要价值。本文综述了已知或可推断出该特征的藻类中的绝对取向模式。除绿藻纲外，所有类别的藻类均呈现逆时针绝对取向，被认为是原始的；而绿藻纲大多数成员中存在的顺时针绝对取向是进化过程中各组成部分逐渐顺时针旋转的结果。记录这种旋转的现存中间类型包括营养细胞呈现逆时针绝对取向的哈夫尼藻属，以及鞭毛器除微管小根有轻微顺时针偏移外严格呈十字形的四鞭毛盘星藻游动孢子。鞭毛器中基体的V形排列，以及细胞体上近端鞘和两层鳞片的存在，进一步将盘星藻游动孢子确定为绿藻纲内的一种原始细胞类型。基体从鞭毛孔顶端或侧面伸出的趋势、四鞭毛细胞的消失，以及在绿藻纲中基体偏移量的增加，表明各纲内的进化进程。在鞭毛器复制和发育过程中，绝对取向是保守的。在所研究的藻类中，鞭毛器分裂后的事件可细分为成分组装，这是普遍存在的且保留了系统发育上有用的特征，以及成分重新定向，这在相对较少的绿藻中发生，使鞭毛器适应特殊功能。基于这些鞭毛器取向研究，提出了对绿藻纲内进化的重大重新评估，具有离体细胞分裂（如盘星藻属）的弱叶状体藻类被认为是原始的，而包括团藻目在内的大多数其他类型则被认为更高级。壁形成的进化并不排除原始绿藻属中鳞片的形成。此外，绿藻中可能存在一个或多个先前未描述的主要谱系，包括一个多列藻谱系，其成员具有背腹扁平的游动细胞、鞭毛器的逆时针绝对取向以及胞质分裂时的藻质体。绿藻纲、石莼纲和多列藻谱系被认为有一个类似于现代扁藻属的共同祖先，而轮藻纲则被认为起源更为古老。
