Origin and evolution of shoot apex in vascular plants.

维管植物茎尖的起源和进化。

• 批准号: 13640704
• 负责人: IMAICHI Ryoko
• 金额: $ 0.77万
• 依托单位: Japan Women's University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640704/
• 关键词: shoot apex; apical cell; plasmodesmata; TEM; evolution; Spermatopyta; Filicopsida; Lycopsida; 維管束植物; 小葉類; 大葉類

The frequency and distribution of plasmodesmata (PD), intercellular channels, in the shoot apices was calculated using TEM sections, and compared between Pteridphytes and Spermatophytes to discuss the evolution of the three types of shoot apices in the vascular plants: the monoplex-, the simplex- and the duplex-types. In the monoplex shoot apices of the Filicopsida, the Equisetopsida, and the Psilopsida, the cell walls of apical cell has the greatest number of PD, and those of cells apart from the apical cell the lower number of PD. There is a gradient in PD frequency from the apical cell downward. The Pteridophytes are believed to lack secondary PD, and then PD network in the plant body is cell llneage-specific. In contrast, the simplex shoot apex typical of the Gymnosperms exhibits very low PD frequency with no gradient in a shoot apex. This is the same as the duplex shoot apex typical of Angiosperms. It is plausible that the Gymnosperms also have the ability to form secondary PD and construct interface-specific PD network. This fact is consistent with the currently accepted story that the evolution of the leaf (megaphyll) and stem occurred independently in the two different phylogenetic lines. In the micorphyllous Lycopsida two types of PD network, the lineage-specific and the interface-specific, are recognized. The former is characteristic for the Selaginellaceae shoot apices with the single apical cell, and the latter for the Lycopodiacae with plural apical cells. It seems likely that the Lycopodiaceae gains the ability to form the secondary PD after they branched off phylogenetically from the rest of the vascular plants. It is noteworthy that presence of single apical cell or plural apical initials results in drastically different shoot apex organizations with respect to cell-to-cell PD network.

利用透射电镜（TEM）切片计算了茎尖胞间连丝（plasmodesmata， PD）的频率和分布，并与蕨类植物和精生植物进行了比较，探讨了维管植物茎尖单一型、单一型和双一型的进化过程。在蓼科、马角蕨科和裸蕨科的单茎尖中，顶细胞细胞壁的PD数最多，除顶细胞外的细胞细胞壁PD数较少。PD频率从顶细胞向下呈梯度。认为蕨类植物缺乏次生PD，因此植物体内的PD网络具有细胞特异性。裸子植物单形茎尖的PD频率很低，且无梯度。这与被子植物典型的双面茎尖相同。裸子植物也可能具有形成次级PD和构建特定界面PD网络的能力。这一事实与目前公认的叶片和茎的进化在两个不同的系统发育系中独立发生的故事是一致的。在小叶松属植物中，可以识别出谱系特异性和界面特异性两种类型的PD网络。前者表现为卷柏科的茎尖单根细胞，后者表现为石松科的茎尖多根细胞。似乎石松科植物在系统发育上从其他维管植物分支出来后获得了形成次生PD的能力。值得注意的是，单根尖细胞或复数根尖的存在导致茎尖组织在细胞-细胞PD网络方面有很大的不同。