Abstract
The orientation and morphology of the female cone are important for wind pollination in gymnosperms. To examine the role of female reproductive structures associated with wind pollination in Ginkgo biloba, we used scanning electron microscopy and semithin section techniques to observe the development of female short shoots and ovules in G. biloba before and during the pollination period. The ovule differentiation process was divided into six stages: undifferentiated, general stalk differentiation, integument differentiation, nucellus differentiation, collar differentiation, and mature stage. Before the pollination period, the integument tip generated the micropylar canal and the micropyle, while the nucellus tip cells degenerated to form the pollen chamber. During pollination, the micropylar canal surface became smooth, the micropyle split into several pieces and bore a pollination drop, and the pollen chamber directly faced the straight micropylar canal. The leaves and ovules were spirally arranged on the female short shoot, with the ovules erect and the fan-shaped leaves bent outwards and downwards. The ovules of G. biloba have differentiated some special architectural features adapted for pollen capture and transport. Together, these structures constitute a reproductive structural unit that may improve wind pollination efficiency at the female level.
Highlights
Pollination is an important process in the life cycle of seed plants
Based on the results of such studies, it was concluded that adaptive characteristics to wind pollination that contribute to the pollination mechanisms of gymnosperms involve (1) orientation of the ovulate cone, as well as ovule structure and position at the time of pollination [2, 5]; (2) pollen characteristics, especially the presence or absence of sacci [6, 7]; (3) whether a pollination drop appears at pollination or not [8, 9]
We present morphological data that clarify the relationships between female reproductive structures and wind pollination in G. biloba, providing further insights into the wind pollination mechanisms in gymnosperms
Summary
Pollination is an important process in the life cycle of seed plants. During the evolution of angiosperms, diverse forms of pollination with complex mechanisms have evolved. Based on the results of such studies, it was concluded that adaptive characteristics to wind pollination that contribute to the pollination mechanisms of gymnosperms involve (1) orientation of the ovulate cone, as well as ovule structure and position at the time of pollination [2, 5]; (2) pollen characteristics, especially the presence or absence of sacci [6, 7]; (3) whether a pollination drop appears at pollination or not [8, 9] Among these characteristics, the ovule as the female reproductive organ varies widely in its morphology among gymnosperms. Based on our previous studies [21, 23], in this paper we investigated the morphological and structural development of female short shoots and ovules in G. biloba, focusing on ontogenetic features and their relationships with pollen capture. We present morphological data that clarify the relationships between female reproductive structures and wind pollination in G. biloba, providing further insights into the wind pollination mechanisms in gymnosperms
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