Study On Floral Organogenesis And Embryonic Development Of Clematis ‘Ernest Markham'

There are more than 300 kinds of native species and more than 3000 kinds of varieties in the genus of Clematis(Ranunculaceae),which have the important value of garden applications.According to cultivation characteristics and maintenance requirements,Clematis can be divided into three categories.C.‘Ernest Markham' belonging to Late-flowering Clematis was chosen as the experimental material.Floral buds differentiation,megasporogenesis,microsporogenesis,male and female gametophyte development and double fertilization were observed by traditional paraffin section technique,and the main results were as follow.(1)Anatomy of floral buds differentiation.There were sepals,stamens and pistils from outer to inner in the mature floral organs' structure of C.‘Ernest Markham'.The differentiation of floral organs could mainly be divided into 3 stages.They consisted of floret primordia differentiation,stamen primordia differentiation and pistil primordia differentiation,which took approximately 25 days during the total process of floral bud differentiation.Among the three developmental stages,the stage of floret primordia differentiation developed a little slowly.The floral organ development pattern of C.‘Ernest Markham' was similar to the ABC model of Santalales and Caryophyllales plants.It was the single-wheel and centripetal developmental model.(2)Megasporogenesis,microsporogenesis,male and female gametophyte development and double fertilization.The structure of anther wall was the monocotyledonous type,which was composed of epidermis,endothecium,one or two middle layers and tapetum.Fibrous thickenings were generated in the endothecium when the anthers were mature.Tapetum was secreted type.Simultaneous cytokinesis in the microsporogenesis developed into a decussate tetrad of microspores.Mature pollen grains were 2-celled and spheroidal when they dehisced;with tricolpate germinal furrow;the ornamentation of pollen's surface was granular;the contour line of pollen exine was wavy and smooth.The ovule was anatropous and tenuinucellate.In general,simultaneous cytokinesis in the megasporocyte developed into a T-shape tetrad;the megaspore near chalaza gradually developed into the functional megaspore,the other three megaspores gradually degenerated and died;the megaspore near chalaza of the tetrad produced a Polygonum-type embryo sac.The pattern of fertilization was micropyle fertilization.The pollen tube went into the embryo sac and released two sperm 4~6 h after pollination.Double fertilization occured in the embryo sac approximately 40 h after pollination.The sperm and the egg cell fused with each other,creating the zygote.The zygote began division 6~7 days after pollination.Histological observation could be seen that it had a good deal of starch grains and protein during the meiosis of microspore.It also had a mass of polysaccharide,protein and lipid in the tapetum and pollen wall,which provided basis to explore the energy metabolism in the process of embryonic development of Clematis ‘Ernest Markham'.The above observations firstly revealed characteristics of embryonic development of C.‘Ernest Markham'.It provided valuable experimental data for the study on the embryological features of ornamental-type Clematis plants.In addition to this,it established the theoretical basis for the study on the cross breeding and new varieties cultivation of Clematis plants.