烏來杜鵑之胚胎學

Abstract

烏來杜鵑(Rhododendron kanehirai Wilson)屬杜鵑花科，杜鵑花屬，為臺灣特有種。半落葉性灌木，花兩性，每年二月到四月開花，蒴果八月至十月成熟開裂。 花原體於九月下旬起自頂端分生組織凸起。十月上旬花萼原體出現，花冠裂片、第一輪雄蕊、第二輪雄蕊與心皮原體於十月中旬後陸續形成出現。花萼5枚。花冠裂片5枚，部分合生。雄蕊10枚，二輪，花藥具二藥瓣，各有兩個花藥囊。雌蕊具5枚心皮，早期合生。 十月下旬時花藥原體可分為原始表層與中央細胞團。花藥壁層由一層表皮層，一層內壁層，一或二層中間層，一或二層營養層所構成。營養層細胞為腺體型。花粉母細胞減數分裂後細胞質同時型分裂。小孢子四分體為四面體型。成熟花粉始終維持四分體型式，具二細胞，三溝孔。單一花粉粒大小為25-27.5µm。花藥孔裂。 十月中旬起心皮向內合生並與中軸連合形成中軸胎座。十一月中旬時胚珠原體凸出胎座表面。每一子房室內約可產生160-240枚胚珠。胚珠倒生，單層珠被。大孢子孢原細胞起源於珠心次表皮層，並直接行使大孢子母細胞功能，為薄珠心。大孢子母細胞減數分裂產生直線形大孢子四分體。合點端大孢子發育為胚囊母細胞。胚囊發育為蓼型。兩個極核在雙重受精前融合。反足細胞早期退化消失。 初生胚乳核第一及第二次分裂為核型，第三次之後為細胞型。具合點端與珠孔端胚乳吸器。胚胎發生為茄型。成熟種子具胚乳，子葉二枚。

Rhododendron kanrharai is an endemic species to Taiwan, which belong to the Ericaceae, Rhododendron. The small trees are half-deciduous, bisexual flowers. Flowers are produced from February to April; capsule dispersed from August to October in the year. Flower primordia are emerged from the shoot apical meristem in late August. The primordia of sepal occur in early September. The primordia of corolla lobe, stamen and carpel emerged successively after mid September. Sepal 5, corolla lobes 5, partial combine. Stamens 10, two whorls and anther are two theca, which has two anther sacs. The pistil composed of 5 carpels which are early closed. Anther primordia are composed of the protoderm and the central cell mass in late September. The anther wall consist of an epidermis, one endothecium, 1 to 2 middle layer and 1 to 2 tapetum in December. The tapetum is of the glandular type. The microspore mother cells undergo meiosis, the tetrahedral tetrads of microspores are formed by simultaneous cytokinesis. The pollen grains still to keep tetrahedral form. Each pollen grain is 2-celled, 3-colporate and 25-27.5µm in size. Anther dehiscence is poricidal. The carpel closed toward and connected with the ovary central column to form axile placentation since mid October. Ovule primordia occur from placenta in mid November. An ovary locelle produced about 160-240 ovules. Ovules are anatropous, unitegmic. The single megaspore archesporial cell origins from nucellus hypodermal layer and becomes the megaspore mother cell directly, which as tenuinucellate. The megaspore mother cell meiosis to form a linear megaspore tetrad. The chalazal end megaspore develops into the embryo sac mother cell. The development of embryo sac is Polygonum type. Two polar nuclei fuse before fertilization. Three antipodal cells are ephemeral. First two divisions of endosperm are nuclear, and the next divisions are cellular. Two end endosperm haustoria. The embryogeny is identified to the Soland type. Each seed consist of endosperm and 2 cotyledon embryo.