F. Bidentis Reproductive Biology

The formation of scorpioid cyme, capitulum and floret of Flaveria bidentis (L.) Kuntze was observed under scanning electron microscopy. The inflorescence of F. bidentis was composed of the main axis with three orders branches in a decussate arrangement. Scorpioid cymes (3-6) were developed at the apex of the main inflorescence axis as well as lateral axes. Each scorpioid cyme had 5-15 capitulums which was consist of 4-11 florets. For the floral development process, petal primordia arose firstly, then stamen primordia appeared, followed by two carpel primordia. In 2007, florescence of bidentis was from late July to late September in Tianjin. In Mid July, the inflorescence primordia and floret primordia were formed and differentiated continually, and approximately 15 days after the initiation of flower bud differentiation, individual floret was well formed.Microsporogenesis, the development of male gametophyte of F. bidentis were observed by using method of traditional paraffin sections. The results showed that anther was tetrasporangiate, and the development of anther wall was the Basic type, which included an epidermis, an endothelium, a middle layer and a tapetum. The tapetum belonged to amoeboid type and its cells were binucleate. From appearance of archesporial cells to 2-celled polen stage, the development of tetrasporangiate was asynchronous. The archesporial cells differentiated from single archesporium, the meiosis of microspore mother cells (MMC) were continuous type and tetrads were tetrahedral. Mature pollen grains were 2-celled with 3 aperture, and obvious spines on thick extine. Huge pollens were observed occasionally. At the MMC stage, the tapetum membrane was formed from the middle layer neighboring tapetal cells, which surrounded tapetum and MMC.Megasporogenesis, megagametogenesis and embryogenesis of F. bidentis were as following:the ovary was bicarpellate, unilocular, one ovules and basal placenta; the ovule was unitegmic, tenuinucellate, anatropous and with developed endothelium; archesporial cell of megaspore differentiates immediately below the nucellar epidermis and functions as megasporocyte after development, and then, the megasporocyte undergoes meitotic to form a linear tetrad, one micropyle megaspore in linear tetrad becomed the functional megaspore; the embryo sac was of the Monosporic Type; the mononucleate embryo sac underwent three successive divisioned to form a mature embryo sac with seven cells. The mature embryo sac had an egg and two synergids near the micropyle and a central cell in the center, three antipodal cell in the chalazal.The embryo underwent the stages of globular embryo, heart embryo, and torpedo embryo to develop into mature cotyledon embryo. The development type of the endosperm was Cell Type, and the embryogeny belonged to the Asterad Type.