侧柏珠孔闭合过程及其进化生物学意义

Study on micropyle closure in Platycladus orientalis and its evolutionary significanc

【目的】探究侧柏珠孔闭合过程,以丰富裸子植物珠孔闭合数据,为研究裸子植物系统发育提供参考。【方法】以侧柏雌球花为材料,通过石蜡切片及扫描电子显微镜等形态学方法观察授粉后胚珠发育过程;同时基于珠孔闭合方式对本内苏铁和其他现存裸子植物进行聚类分析。【结果】(1)侧柏花粉进入胚珠后,珠孔端珠被最内侧2层细胞开始辐射状向内横向生长,直至将珠孔完全堵塞。(2)侧柏珠孔闭合过程中,珠被细胞为长圆锥形,细胞层数增多至4~6层。(3)裸子植物珠孔闭合方式可分为4类:其中苏铁、银杏为一类,松属植物与罗汉松科植物为一类,本内苏铁单独一支,侧柏及其他种聚为一类。【结论】侧柏珠孔闭合过程不同于苏铁类植物和银杏,但与松科植物及本内苏铁的珠孔闭合过程类似,这暗示本内苏铁与现存松柏类植物在珠孔闭合有一定的演化关系,为理解裸子植物生殖系统演化提供新的形态学依据。

[Objective]In order to enrich the data for the study of micropyle closure in gymnosperms and to provide a reference for the phylogenetic study of gymnosperms,micropyle closure of Platycladus orientalis Franco was investigated.[Methods]Female cones of P.orientalis were sampled and examined using morphological techniques,including paraffin section and scanning electron microscopy.In addition,cluster analysis of the mode of micropyle closure was conducted for Bennettitales.[Results](1)After pollen enters the ovule,the innermost two cell layers of the integument began to grow radially inward until the micropyle was completely closed.(2)During the micropyle closure,the innermost cells of the integument were elongated and became conical in shape,with the cell layers typically increased to 4 to 6 layers.(3)The micropyle closure of gymnosperms could be divided into four clades:One for Cycas and Ginkgo,one for Pinus and Podocarpaceae,a separate group for Bennettitales,and a cluster of P.orientalis and othe species.[Conclusion]The micropyle closure of P.orientalis differs from Ginkgo and cycads,which is similar to Pinus and Bennettitales.This study suggests that there is an evolutionary relationship in micro-pyle closure between Bennettitales and existing conifers,providing novel morphological evidence for the understanding of evolution of the reproductive systems of gymnosperms.