阔叶杨桐衍生胎座的发育特征(五列木科)

Developmental characteristics of deuterogenic placenta in Adinandra latifolia(Pentaphylacaceae)based on SEM observation

关键词:  阔叶杨桐, 五列木科, 衍生胎座, 特立中央胎座, 扫描电镜

Key words:  Adinandra latifolia, Pentaphylacaceae, deuterogenic placenta, free central placenta, SEM

摘要:

为观察五列木科阔叶杨桐子房中衍生胎座的发育过程,探明衍生胎座与心皮源胎座及特立中央胎座的关系,该研究采用扫描电子显微镜和体视显微镜相结合的方法,详细观察了阔叶杨桐的花芽和成熟果实。花芽采集后经FAA固定、酒精-乙酸异戊酯梯度脱水、液体CO₂干燥、扫描电子显微镜下观察; 将成熟果实直接在体视显微镜下解剖观察。结果表明:阔叶杨桐花芽发育过程中,雄蕊原基发生后,5心皮快速发生,先愈合形成上部具有中轴胎座、下部是空腔的子房; 接着心皮上长出胎座(心皮源胎座),在其下部空腔内与心皮相对的位置,花托顶端出现多个凸起,并逐渐愈合成半球形的衍生胎座,心皮源胎座和衍生胎座上出现多枚可育胚珠。成熟果实中,心皮源胎座和衍生胎座上均有种子,二者之间没有维管束联系。因此,衍生胎座与心皮源胎座独立发生,且晚于心皮源胎座; 阔叶杨桐衍生胎座的发育过程不同于石竹科和商陆科的特立中央胎座(中轴胎座隔膜消失形成),而与杜鹃花目报春花科、假轮叶科、杜茎山科和紫金牛科的特立中央胎座类似(在花托顶端直接形成)。

Abstract:

In order to reveal the developmental process of the deuterogenic placenta of Adinandra latifolia from the family Pentaphylacaceae, and the relationship between deuterogenic placenta, carpellary placenta and free central placenta, the flower buds and mature fruits of A. latifolia were observed in detail by scanning electron microscope(SEM)and stereoscopic microscope. Floral buds at different stages of development were collected and fixed in formalin-aceticacid-alcohol, and then dehydrated through an ethanol/amylacetate series, critical point dried with CO₂, Au/Pt sputter coated, prepared samples were examined with SEM. Mature fruits were dissected under a stereoscopic microscope directly without preparation. The results showed that during the floral development, 5 carpel primordia were growth rapidly after the stamens initiation, and then ovary was combined with the axial placenta on the upper part and cavity on the bottom part. After the placenta grew on the carpels(named carpellary placenta), several mounds appear at the top of the receptacle within the position opposite to the carpel in the lower cavity. The mounds combined gradually into a hemispherical deuterogenic placentation. And some fertile ovules appeared on the surface of both the carpellary placenta and deuterogenic placenta. Finally, in mature fruits the fertile ovules turn to seeds on both types of placenta in which vascular bundles are discrete. Therefore, deuterogenic placenta appeared independently and was later than the carpellary placenta. The development of deuterogenic placenta in A. latifolia was different from that of the free central placenta in both Caryophyllaceae and Phytolaccaceae(the axial placenta turned into a free central placenta by the septa disappear), but it is basically identical to that of Primulaceae, Theophrastaceae, Maesaceae, Myrsinaceae from Ericales(the free central placenta formed on top of the receptacle directly).