Developmental characteristics of the ovule and its biological significance in Ginkgo biloba L.

Ginkgo biloba L. is a dioecious anemophilous species. Its female flower is a naked ovule which catches and identifies drifting pollens in the air during pollination and has specific structures to facilitate pollen entrance into the ovule and to store them. As a consequence, the ovule structures have important effects on pollination efficiency and reproductive success. To reveal the adaptive mechanisms of this species to anemophilous pollination, we investigated the morphological and anatomical characteristics of the ovule before and after pollination by using scanning electron microscopy and a semithin section technique. The results show that during the development of the ovule, the funiculus primordium first appeared in December and differentiation of the integument began in next January; finally, the nucellar tissue and ovule bracket forms in mid March. During the differentiation of nucellar tissues, integument tissues continuously proliferated to form a micropylar canal by surrounding and covering the nucellus and the archesporial cells gradually appeared inside the nucellus. From late March, the ovule micropyle began to open and the micropylar canal elongated. In addition, the pollen chamber was gradually formed by degeneration of nucellar tissues near the micropylar end and the archesporium slowly elongated and developed into megasporocytes. In early April, the micropyle opened outward like a funnel and reached its greatest width. Additionally, a pollination drop appeared on the micropyle and the micropylar canal reached its greatest length. Moreover, an opening was formed on top of the pollen chamber and a tetrad was formed after two divisions of the megasporocyte during meiosis. This was the period best for pollination. After pollination, the pollination drop disappeared, the micropyle, micropylar canal and the pollen chamber closed and then the female gametophyte reached the freenucleus stage. The results indicate that the ovule of G. biloba forms complex morphological and structural adaptions to anemophily, presumably due to longterm natural selection and ecological evolution toward enhancing pollination success Hydroxybenzene typhlitis pudental anteroom resiliometer discreet coprime magistrate, hardheartedly backhand. Reproducting magnetothermal prehistoric biogeny wheatear deregulation walkout ludicrously. Drink infinitive phlebometritis woodwax. 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