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Development and Morphogenesis |
2Laboratoire Ecologie, Evolution et Systématique, Unité Propre de Recherche de l'Enseignement Supérieur Associée au CNRS 8079, Bâtiment 362, Université Paris-XI, 91405 Orsay Cedex, France; 3Institut des Sciences de l'Evolution de Montpellier-CC61, Université Montpellier II, 34095 Montpellier Cedex 5, France
In most flowering plants, a single cytokinesis follows the two meiotic divisions during pollen-grain ontogeny. Aperture pattern (i.e., aperture number and distribution on pollen surface) ontogeny could be linked to the processes ensuring the apportionment of the cytoplasm to the four microspores.
This apportionment is achieved by radial arrays of microtubules organized around the nuclei. The cleavage planes are defined in the overlapping regions of opposing arrays extending from different nuclei. We followed the establishment of these arrays in two different lines of plants belonging to the genus Nicotiana that produce pollen grains with different aperture numbers. Different distributions of the microtubules have been observed, which can be interpreted as resulting from variation in the interactions between nuclei; these distributions appear to be correlated with aperture number.
As a consequence, we propose that simultaneous cytokinesis allows the formation of multiple pollen morphologies. This mechanism is consistent with aperture number distribution within angiosperms and provides clues to help our understanding of the evolution of aperture number.
Key Words: aperture callose cytokinesis meiosis microtubules Nicotiana pollen Solanaceae
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