Morphological, Cytological And Ultrastructure Observation On Flower Development Of Brassica Campestris Ssp. Chinensis

Molecular mechanism of flower development has been the focus of several study fields. Speculating the function and expression model of a gene through observing the behaviors of its mutants during flower development is general applied and effective .Cloning and function analysis allow us to confer the action mechanism and function of a gene. Addition to the phenotype of the gene mutants, we can find out the sense of the fine structures and phenomena that are abnormal in the mutants to flower development. The study of flower development and study of correlative genes are two processes that supplement each other and bring out the best in each other. So, in order to find out the abnormal phenotype of mutants, it is necessary to study the flower development in detail.In this paper, morphological, cytological, and ultrastructural characters of Chinese cabbage-pak-choi (Brassica campestris L. ssp. chinensis Makino, syn. Brassica rapa ssp. chinensis) flower development is described from initiation until the opening of the bud. Studies and results are as follow:(1) Because buds of the same whorl in a inflorescence are almost of the same size, buds of a inflorescence are belong to 21 stages according to their whorl sequence. In term of flower organ primordia, lenth of flower buds, and pollen and anther development, the flower development of Chinese cabbage-pak-choi are divided into 21 stages.(2) Length of flower buds and organs at stages 7 to 21 has been measured with stereo microscope. The morphogenesis, growth rate, and surface structrure of floral organs at all the 21 stages have been observed with environmental scanning electron microscope. The early stages we divided are almost the same as that of Arabidopsis divided by David in 1990. We have more late stages than Arabidopsis, in that the develoqment process is much more exactly described. This is designed to accord with the development of pollen and anther. As for the floral organ initiation, the order is sepal, petal/stamen, gynoecium The lateral sepals arise earlier than the adxial sepal. The long stamens arise earlier than short stamens. There is a delay in petal development at the early stages and the petal begins to grow rapidly at stage 15. The filament begins to growth at stage 17. The height diference of long and short stamen is caused by the high and low location on the floral primordium at early stages and diference length of long and short filament at late stages. The early gynoecium was an oval, hollow tube. At later stages, the hollow tube closed and a swallow groove left so that the mature stigma is bifid. On the outer surface of the sepal and the surface of the nectary, many stomata are dispersed. On the abaxial surface of the stamen, near to the midrid, there are some stomata as well. The surface cells of the sepal and the stamen have cuticurlar thickenings. The midrid cells of the abaxial surface of the anther are strikingly larger than the adjacent cells.(3) Semithin sections of flower buds at stages 8 to 21 are made Pollen and anther development process and charaters are studied with light microscope. The anther development is of the dicotyledonous type. The tapetum is glandular. Deep-stained grains appear in the connective tissue and anther wall tissue from sporogenous stage to tetrad stage. Probably, they are strarch grains. During the vacuolating stages, the microspores contract badly and are irregular shaped. At the late uninucleate microspore stage, the tapetum is deformed and some of the microspores somewhat slump into the tapetum.(4) Ultrathin sections of flower buds at stages 8 to 21 are made. Ultrastructure of microspore, male gametophyte and tapetum development at these stages has been studied with transmission electron microscope. During the microspore and male gametophyte development, cytoplasmic reorganization happens two times. The first cytoplasmic reorganization occurs at meiosis stage I and the second occurs at middle and late uninucleate microspore stage. After the microspores are released, sporopollenin and fibrillar layer deposit probably through fibillar material-beared vecules in the tapetum cell fuse with the cytomembrane and release their content to the anther locule. Ubisch bodies are not found during tapetum development. The inner tangential wall and radial walls degenerate at meiosis prophose I and new low electron-dense walls form at anaphase I /telophase I . The new radial walls degenerate at the early uninucleate stage and the inner tangential wall retains until the early two-cell stage. At the late stages, the tapetum cells are occupied by tapetosomes and elaioplasts. Mature pollen grains are enveloped by a tryphine. The tapetum breaks up , tapetosomes and elaioplasts flow into the locule and deposit onto the pollen wall to form the tryphine.(5) The flower development stages 8 to 21 of Chinese cabbage-pak-choi are respectively corresponding to sporogenous stage, early microspore mother cell stage, stage just before meiosis, meiosis pachytene/diplotene, meiosis anaphase I /talophase I , tetrad stage, early uninucleate stage, middle uninucleate stage, late uninucleate stage, early two-cell stage, middle two-cell stage, late two-cell stage, early three-cell stage, and mature pollen stage.