Pollen ontogeny in Magnolia liliflora Desr. |
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Authors: | B G Galati G Zarlavsky S Rosenfeldt M M Gotelli |
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Institution: | (1) Facultad de Agronom?a, C?tedra de Bot?nica Agr?cola, Universidad de Buenos Aires, Buenos Aires, Argentina;(2) Facultad de Ciencias Exactas y Naturales, Departamento de Biodiversidad y Biolog?a Experimental, Universidad de Buenos Aires, Buenos Aires, Argentina |
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Abstract: | Pollen ontogeny contributes significantly to the evolutionary analysis and the understanding of the reproductive biology of
seed plants. Although much research on basal angiosperms is being carried out there are still many important features about
which little is known in these taxa, such as the sporophytic structures related to pollen development and morphology. In this
study, pollen development of Magnolia liliflora was analyzed by optical microscopy and transmission electron microscopy. The aim of this paper was to supply data that will
help characterize basal angiosperms. Microsporogenesis is of the successive type, so that tetrads are decussate or isobilateral.
The callosic walls form by the centripetal growth of furrows. The secretory tapetum develops orbicules, which start to form
in the microspore tetrad stage. Pollen grains are shed at the bicellular stage. The exine wall has a granular infratectum.
Ultrastructural changes observed in the cytoplasm of microspores and tapetal cells are related to the development of the pollen
grain wall and orbicules. Centrifugal cell plates are more usual for the successive type of microsporogenesis. The presence
of the successive type of microsporogenesis with callosic walls formed by the centripetal growth of furrows could reflect
the fact that the successive type in Magnoliaceae is derived from the simultaneous type. The granular infratectum of the ectexine
and the presence of orbicules could indicate that this species is one of the most evolved of the genus. |
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