Embriologia de Miconia albicans (Sw.) Triana (Melastomataceae), especie agamospermica / Embriology of Miconia albicans (Sw.) (Melastomataceae), agamospermous species

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Miconia albicans (Melastomataceae) is a species with diplosporic obligate agamospermy and no pollen viability in ?Cerrado? and Atlantic Forest vegetations. The sterility of pollen grains wasn?t restricted to one developmental stage and the major abnormality of the cells from pre-anthesis flower anthers was the deformation of the reproductive cell wall, mainly in the free microspore stage. Intense vacuolation of both sporogenous and tapetal cells as well as the precocious degeneration of the tapetal cells may be related to male sterility in this species. The ontogeny of the parietal layers was different from that observed in another species of the genus and was in agreement with its classification of irregular type. The anthers in predehiscence stage showed the dehiscence region probable closed with an epidermis with papilous cells, differently from that observed in the another anther regions. Ambient differences were restricted to the number of cells observed in the pre-anthesis anthers, which was about 50 percent up in the Atlantic Forest vegetation in relation to the Cerrado one. The ovule and embryo sac ontogeny was similar to that observed in another species of the genus, except for the division of the arquesporic cell and the suppression of the meiotic division during the gametogenesis, both observed only in M. albicans. The agamospermous embryos were originated in the embryo sac from the egg cell or one of two synergids. Evidence suggested that the nuclear autonomous endosperm was originated from expansions in both nucleus of the central cell, and not from the fusion of both. The percentage of ovule abortion was about 50 percent and the mature seeds showed a variable germination percentage probably due to fungi incidence which occurred in the seeds from both environments. The ontogenetic characteristics observed in fruits from both floral buds and flowers were similar, as well as the seeds viability

ASSUNTO(S)

esporogenese gametogenesis apomixis apomixia melastomataceae gametogenese melastomataceae agamospermia agamospermy sporogenesis

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