Evolution of gametophytes molphologies of Pteridophytes

配子体蕨类植物的形态多样，有块茎状、心形叶状、带状、带状和丝状。这些配子体的形态与蕨类植物的进化有关。块茎状配子体在地下，具有内生真菌，并且在石松植物、阴地蕨属和裸盖蕨属中发现，后两者是蕨类植物的早期分支的植物群。薇菜是细孢囊蕨类植物的第一个分支，在早期发育阶段就具有大量的配子体。其余蕨类植物的配子体多为心形，很少有带状或不规则形。这些事实表明，块状块茎型是原始的，心形型是从块茎型演化而来的，然后在高级类群如水龙骨科和书带蕨科中演化出带状或不规则形状的配子体。我们比较了配子体的发展，在许多蕨类植物类群使用连续观察技术。阴地蕨科植物孢子萌发后，细胞随机定向分裂形成配子体，随后分化出顶端分生组织，顶端细胞为三面体。在紫萁科中，块状体仅限于早期配子体的后部，在前部形成一层细胞厚的两侧顶端细胞。由于顶端细胞的活动，心形部分被添加到块状部分。在其他蕨类植物的心形配子体中，早期的大量部分完全缺乏。结果表明，由于缺乏块状部分，以及两侧顶细胞的额外增加，导致了块状细胞向心形细胞的转变。在带状配子体中，有一个顶端细胞，但顶端分生组织的活性比边缘分生组织弱，边缘分生组织紧邻前者。在不规则形状的配子体中，顶端分生组织在发育早期消失，代之以边缘分生组织。

Gametophytes. of Pteridophytes show wide variety of forms, i.e. tuberous, cordate-thalloid, strap-like, ribbon-like, and filamentous shapes. These gametophyte forms have been developed in relation to Pteridophyte evolutions. The tuberous gametophytes are subterranean with endophytic fungi, and found in lycophytes, and Botrychium and Psilotum, the latter two of which are plant groups of early branch of ferns. Furthermore Osmunda, the first branch of the leptosporangate ferns, has been known to have massive gametophytes at early stage of development. The gametophytes of the rest of ferns are mainly cordate, and rarely ribbon-like or irregular in shape. These facts suggest that massive tuberous forms are primitive and cordate formes are derived from tuberous forms, and then ribbon-like or irregular shaped gametophytes are evolved in advanced groups such as Polypodiaceae and Vittariaceae. We compared gametophyte developments in many fern taxa using the sequential-observation technique. Tuberous gametophytes of Botrychiaceae are formed due to cell divisions in random orientation after spore germination, and the apical meristem with three-sided apical cell are differentiated later. In Osmundaceae, the massive part is only limited to posterior part of the early gametophyte, and two-sided apical cell is formed in anterior portion one cell layer thick. Due to activity of the apical cell, cordate part is added to the massive part. In cordate gametophytes of other ferns, early massive portions are totally lacking. It is concluded that shift of shape from the massive to the cordate has been conducted by lacking of massive portion, and additional gain of the two-sided apical cell. In ribbon-like gametophytes, there is an apical cell, but the activity of the apical meristem is weak compared to the marginal meristem, which is next to the former. In irregular-shaped gametophytes, the apical meristem disappears at early developmental stage, and is replaced by the marginal meristem.