O genero Dahlstedtia Malme : embriologia, sistema reprodutivo e biossistematica

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

Flowers, fruits and seed abortion was studied in two Brazilian species: Dahlstedtia pinnata e D. pentaphy/la (Leguminosae, Papilionoideae). Such a study was developed through investigations of: 1. floral development, microsporogenesis, ovule and early seed development following open, self- and cross-pollination, in order to compare the results to other papilionoids and to verify the occurrence of abnormalities in the process; 2. chromosome number, meiotic behavior and meiotic index, in order to verify if pollen grains can limit the fertilization events; 3. fruiting pattern related with position within the inflorescence and ovule degeneration and seed development related with position within ovaries and fruits; 4. geographical distribution, flowering and fruiting, gene flow possibility and their eftects in the reproductive process and delimitation of the species. Buds, fertilized and unfertilized flowers, fruits and seeds in several developmental stages were utilized in histological studies and in tests of the reproductive strategies adopted by plants. D. pinnata and D. pentaphylla shared common developmental pathways in flower formation of other papilionoids. Anomalies and suppression of floral organs were not found. Differences in characters expressed in early stages of ontogeny in infrageneric taxa are scarce; however, species differed in the distribution of secretory cavities on floral organs. Both species have n = 11 and such a chromosome number has not been reported before. The basic number is also 11, because cytological observations included ali species in Dahlstedtia. Plants of D. pentaphy/la are meiotically stable and pollen grains do not limit fertilization. D. pinnata showed lower meiotic index, and a high number of adventitious shoots, which can indicate that vegetative propagation has a great importance in that species. Embryo sac development is of the «polygonum» type and endosperm development follows the «Nuclear» type. No differences were observed between cross- and self-pollination in pollen germination, pollen tube growth, megagametogenesis, double fertilization and embryogenesis. In ali treatments premature thickening and retraction of cell walls were observed in the integuments and placenta, followed by embryo sac collapse (ovule) or endosperm and zygote failures (seed). Species are self-compatible, with no occurrence of pre- or post-zygotic mechanisms as barriers to selfing. In D. pentaphylla no differences were found in flower pollination and in fruit production according to the region in the inflorescence; or in degenerating ovule and developing seed according to their position within ovary and fruit. Seed abortion is mostly related to the limited maternal resource at fruit and embryo levels rather than the high degree of self-pollination, which can be confirmed by the occurrence of abortive characteristics first in maternal tissues and later in the offspring. 80th species present distribution restrict to Atlantic Forest, but are geographically isolated in State of São Paulo. There are reports for D. pinnata plants in State of Rio de Janeiro and São Paulo, and for D. pentaphy//a in State of São Paulo, Paraná and Santa Catarina. No embryos were observed after interspecific crossing. Fertilization in D. pinnata was avoided by a dense secretion occupying ali micropilar cavity, obstructing the pollen tube enter. Species are not sazonally isolated, but geographically, and it seems that there is not gene flow between species

ASSUNTO(S)

leguminosa anatomia reprodução embriologia

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