| The mechanism of flowering, an unresolved problem of life sciences, has become one of the hottest fields of plant developmental biology since 1990's. Floral development in higher plants normally requires several steps: floral induction, formation of floral meristems, initiation of floral organ primordia and floral organ development. Cucumber (Cucumis sativus L.) is an important horticultural crop and good experimental material for floral development research, because it is an autonomous-flowering plant, and floral bud in the axil of the first leaf can normally be observed. Used this material for their study, Pang et al (1993) established a system for study on the mechanism of the transition from vegetative shoot apical meristem to floral meristem, initiation of floral primordia and floral organ primordia and sex determination. In this paper, the effort of improving this experimental system, morphological changes of floral bud formation, physiological and biochemical analysis at early stage of floral bud differentiation, expression pattern of CFL gene and flowering genetic engineering were investigated, respectively. The main results are as follows:1. The effect of culture and preculture with different medium pH on floral bud formation on cucmber cotyledons was studied. When cotyledons were cultured continuously on inducing medium with pH 6.5, the percentage of floral formation was 55.0; When cotyledons were precultured on medium with pH 7.0 for two days, floral formation was 71.4 %, and the peak of floral bud formation was 20 days ahead of contiuate culture.Synergistic promotion of 2,3,5 - triiodobenzoic acid (TIBA) and paclobutrazol (PP333) to direct floral bud formation was found when cotyledonary nodes cultured in vitro were cut off half blade and full length of hypocotyle. In inducing medium supplemented with 1.0 ~ 1.5 mg / L TIBA and PP333, the highest frequency of floral bud formation was 90 %. Through these efforts, this experimental system has been improved and wide used for further study on floral development in cucumber, because of its simply operating, short period and well repeat.2. The morphological changes in the cotyledonary nodes of cucumber seedlings cultured on inducing floral bud medium (IFBM) and on inducing vegetative bud medium (IVBM) respectively, were studied during 0 to 7 days before decapitation and during 0 to 8 days after decapitation with light microscope. No latent bud was observed at the cotyledonary axils of 7-day-old seedlings. On the first day after decapitation, epidermal and / or subepidermal cells between cut region and base of cotyledonary petiole started to divide. On the second day after decapitation, these dividing cells resulted in globular protuberances. To the sixth day after decapitation, there appear an apparent differentiation between protuberances in seedlings in IFBM and in IVBM, and the former top become blunt and the latter top become tip. In addition, the rare floral bud formation in cut region were observed on the sixth day after decapitation. On the eighth day after decapitation, floral buds with sepal, petal and stamen primordia were formed on the flanks of cut in IFBM. The morphological changes in cotyledonary nodes were studied during 0 to the sixth day after decapitation with scanning electron microscope as well. The results showed that primordia were formed on the same place on the third day, and there appeared a whorl of secondary prominences on the surface of primordia on the fourth day. After further development for two days, the morphological differences between floral and vegetative buds were observed clearly.3. A calcium sensitive period during differentiation of cucumber cotyledonary node was found by exchanging calcium-free medium from medium supplemented with 6.0 mmol /L CaCh. Cotyledonary nodes of cucumber, which cultured on calcium-free medium for 0, 1, 2, 3,4, 5, 6 d respectively, were transferred to medium with 6.0 mmol / L CaCla for 24 h, then returned to calcium-free medium. Cotyledonary nodes cultured on calcium-fr...
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