叶籽银杏授粉期胚珠的形态结构变化

Observation on Changes of Morphological Structure of the Ovules During Pollination Period in Ginkgo biloba L.var.epiphylla

通过树脂半薄切片和扫描电镜技术对叶籽银杏(Ginkgo biloba L.var.epiphylla)叶生胚珠和正常胚珠授粉期的发育过程进行了观察比较。结果发现:授粉前,正常胚珠各组织已分化完全,珠被迅速生长,在珠心顶端逐渐靠拢;而叶生胚珠此时没有珠托和珠心分化,仅有脊状的突起,主要靠突起内的维管束供给营养,随着突起不断发育,有栅栏组织和海绵组织的分化。授粉期,正常胚珠有珠心组织分泌的授粉滴和珠心发生程序性死亡形成的贮粉室;而叶生胚珠未发现授粉滴的存在,已有珠心和珠被的分化,珠孔呈喙状,珠孔道伸长,但在珠孔道的下方没有发生细胞的退化,因此不能形成贮粉室。授粉后,叶生胚珠和正常胚珠进入雌配子体游离核阶段。与正常胚珠相比,叶生胚珠外观形态体积明显偏小,呈不对称发育。对叶籽银杏败育的机理进行了讨论。

Comparative analysis and observation on morphological structure of the epiphyllous ovule and normal ovule during pollination period in Ginkgo biloba L. var. epiphylla using the resin semi-thin section and scanning electron microscopy （SEM） was taken in order to reveal the mechanism of morphogenesis of the former. The results showed that： Normal ovule organizations had already differentiated completely before pollination, and the integument grew rapidly, then drew together in apex of the nucellus gradually in normal ovule. Meanwhile, there were no differentiation in collar and nucellus, but with some ridge gibbosities in epiphyllous ovule which obtained the nutrition from the vascular bundle in gibbosities. Then the palisade tissue and spongy tissue differentiated along with the development of gibbosities. In pollination period, there was pollination drop secreted by the nucellus and then the pollen chamber formed by the programmed cell death of the nucellus in normal ovule. While there was no pollination drop in epiphyllous ovule, besides the collar and nucellus had already differentiated with the rostrate micropyle, the extended micropylar canal. But no pollen chamber was formed because there was no cell degradation in the bottom of micropylar canal in epiphyllous ovule. Then epiphyUous ovule and ovule were into free nuclei stage of female gametophyte after pollination period. In addition, epiphyllous ovule developed asymmetrically and was obviously smaller from appearance than the normal ovule.