Study On Flower Bud Differentiation And Embryology Of Narcissus Tazetta L.Var.Chinensis

This study systematically researched floral bud differentiation and embryological development, and analyzed the dynamic changes of nutrient metabolism and endogenous phytohormones during flowering in single-lobe Narcissus tazetta L.var. chinensis. This paper aims to understanding the corresponding relationship between the bioclimatology and the feature of growth, development and reproductive biology; to reveal system evolution position of Narcissus in the taxonomy, and to improve plant embryo theory. The results are as follows:1. Narcissus tazetta L.var. chinensis floral organs starting differentiate in August during bulb storage period, and the whole process of differentiation took approximately45d with the former stages developing more slowly than the later stages. Floral organs undergo functional development after differentiated, and the duration lasted about120d.2. Using paraffin method and histochemical analysis observed micro-and megasporogenesis as well as male and female gametogenesis of Narcissus tazetta L.var. Chinensis. The results are as follows:The anther wall, whose development is of dicotyledonous type, consists of four layers:the epidermis, the endothecium, two or three middle layers, and the secretory tapetum. Fibrous thickenings are developed in the endothecium when shed. Successive cytokinesis during microsporogenesis results in a decussate tetrad of microspores. Mature pollen grains are2-celled when anthers dehisce. Most of pollen grains abortion occurs during the process of meiosis anaphase to mitosis. Ovary is inferior and trilocular, with axial placenta. The ovule is anatropous, bitegmic, and tenuinucellate. Embryo sac development have the monospore embryo sac (Polygonum type) and bispore embryo sac (Allium type) types. Histochemical analysis showed that the development of tapetum, pollen wall and ovule accompanied by vigorous carbohydrate, protein and lipid metabolism.The systematic significance of embryological characters indicated that Narcissus tazetta is the derived branch from original to evolution groups in Amaryllidaceae.3. The substance which storage in bulb has occurred significantly changes from vegetative stage to floral organs differentiation stage; the concentrations of starch and soluble sugar continuously decreased (mg-g-1·FW-1) and activity of amylase continuously increased. In the stem tips, starch contents maintained at very low levels (0.17mg·g-1·FW-1), lower610-fold than that of bulbs; however soluble sugar presented at high levels (mg·g-1FW-1), the concentration is higher2.02～3.15-fold than that of bulbs. Soluble protein concentrations continuously increased in both bulbs and stem tips during flowering, and mainly distribute in meristem. Narcissus tazetta L.var. chinensis need a mass of soluble sugar as nutrient foundation for flowering.4. Bioactive phytohormonrs GA1, GA3, GA4、IAA, ABA and zeatin (Z) were detected during flowering in Narcissus tazetta L.var. chinensis. Tatal GA concentration increased significantly in reproductive bud. GA1and GA3promote flowering transition, and GA4regulates floral bud development. GA, and GA4have obvious response for the low-temperature signal. Furthermore, IAA plays important roles in floral organ differentiation, microsporogenesis and ovule development, and not sensitive to low-temperature signal. Z and ZR were continuously decreased with developmental stages. ABA inhibited effect and negative regulation for flowering, and the concentrations were decreased significantly with low-temperature treatment.GA, IAA and Z are widely regarded as growth-promoting compounds that positively regulate processes such as seed germination, stem elongation, leaf expansion, pollen tube growth, flower and fruit development and floral transition. ABA, however, has historically and possibly unduly been considered to function as a growth inhibitor. High ratio of (GAs+IAA+CTKs)/cis-ABA play a decisive regulatory role in flowering transition. Low temperature can be eliminated inhibitory substances in the flower buds to promote flower bud development. GA and ABA are major regulatory factors for flower bud differentiation, and high ratio of GA/cis-ABA promotes the transition of vegetative growth to reproductive growth in Narcissus tazetta L.var. chinensis.