Sporogenesis and Gametogenesis of Catalpa bungei(Bignoniaceae)

The microsporogenesis,megasporogenesis and development of female and male gametophytes of Catalpa bungei were studied by paraffin-embedded sectioning technique and whole stain-clearing technique.The results showed that there were two fertile stamens,anthers with four locules.The development of anther walls was classified as dicotyledonous,and the tapetum was of glandular heterotypic.Meiotic divisions in microspore mother cells were followed by smiultaneous cytokinesis and resulted in tetrahedral tetrad,sometimes isobilateral tetrad or decussate tetrad.The all four single nucleus pollen grains were nondisjunction and formed permanent pollen tetrads.The mature pollen grains were 2-celled and nonaperturate.The species showed superior ovary,2-locules,and axial placenta with many ovules.The ovule was anatropous,unitegmic and tenuinucellatae with the endothelium.The single archesporial cell functioned directly as megaspore mother cell.The meiosis of megaspore mother cell formed a linear tetrad,and the chalazal megaspore was the functional one.The development of embryo sac was of polygonum type.The development of stamen was earlier than that of pistil,they synchronized after blossom.It was considered that the barrenness of Catalpa bungei was not due to male or female sterility,although some proportional abortion exist in the development of pistil and stamen.Maybe it was related to pollination,fertilization and post embryonic development.