Sporogenesis and Gametogenesis of Messerschmidia sibirica L.(Boraginaceae)and Their Taxonomic Implications
The systematic position of Messerschmidia L.has been problematic which was ever moved into Tournefortia L.or Heliotropium L.Sporogenesis and gametogenesis in Messerschmidia sibirica were observed using conventional paraffin sectioning and light microscopy to provide embryological data for a better understanding of the systematic position of Messerschmidia.The results were as follows:(1)The anther was tetra-sporangiate,the primarily matured anther wall comprised four layers:the epidermis,endothecium,a middle layer and tapetum,the development of the anther wall was of the Dicotyledonous type,the tapetum with two-nucleate cells was secretary,the epidermis was persistent and the endothecium was irregularly 2-layered with fibrous thickening;(2)Microsporocyte undergone a meiotic division with a simultaneous cytokinesis resulting in a tetrahedral microspore tetrad,the mature pollen grains were 2-celled;(3)The ovule was unitegmic,anatropous and crassinucellate with a long thin micropyle and weak integument tapetum,some of the nucellar tissue was persistent at the stage of mature embryo sac;(4)The development of the embryo sac was of a Polygonum type,the shape of the mature embryo sac was fusiform with polar nuclei fused before fertilization and antipodal cells already degenerated.The embryological characters of Messerschmidia sibirica might be very similar to those of Heliotropium.Considering the stability of embryological characters within genus,the results suggested that it might be suitable to classify Messerschmidia into Heliotropium based on the molecular phylogenies.
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万方数据
维普
