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Abstract

We studied the embryology of Withania somnifera (L.) Dunal by light microscopy in order to reveal specific embryological features of the genus, and compared the results with embryological data on other members of the family Solanaceae. The key embryological characters of W. somnifera include dicotyledonous-type anther wall formation, simultaneous cytokinesis in pollen mother cells, binucleate tapetal cells, 2-celled mature pollen, anatropous, tenuinucellate and unitegmic ovules, polygonum-type embryo sac formation, the presence of an endothelium, and cellular endosperm formation. We give the first report of the dicotyledonous mode of anther wall formation (previously described as basic type) for the species. Comparative study suggests that anther wall formation, number of nuclei in tapetal cells, number of cells in mature pollen, mode of embryo sac formation and endosperm development are the most variable embryological features in Solanaceae. Some of these embryological features of W. somnifera should be of value for comparative study of related species and their phylogenetic relationships within the family.
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Abstract

The embryology of two species, Deschampsia antarctica , a native species, and Poa annua , an alien species in the Antarctic we studied. Flowering buds of plants growing in their natural habitats on King George Island and generative tissues of both plant species grown in a greenhouse were analyzed. Adaptations to autogamy and anemogamy were observed in the flower anatomy of both species. The microsporangia of the evaluated grasses produce a small number of three−celled pollen grains. Numerous pollen grains do not leave the microsporangium and germinate in the thecae. Deschampsia antarctica and P. annua plants harvested in Antarctica developed a particularly small number of microspores in pollen chambers. In D. antarctica , male gametophytes were produced at a faster rate: generative cells in pollen did not become detached from the wall of the pollen grain, they were not embedded in the cytoplasm of vegetative cells, and they divided into two sperm cells situated close to the wall. The monosporous Polygonum type of embryo sac development was observed in the studied species. The egg apparatus had typical polarization, and the filiform apparatus did not develop in synergids. Large antipodals with polyploidal nuclei were formed in the embryo sacs of D. antarctica and P. annua . Poa annua was characterized by numerous antipodal cells which formed antipodal tissue in the chalazal region of the embryo sac. Three distinct antipodals with atypical, lateral position in the vicinity of the egg apparatus were observed in D. antarctica. The diaspores of the investigated grass species were characterized by small size, low weight and species−specific primary and secondary sculpture of the testa and caryopsis coat.
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