Dormancy Regulation Of Chongming Narcissus(Narcissus Tazetta Var. Chinensis)

Dormancy has been extensively studied in plants which experience severe winter conditions but much less so in perennial herbaceous plants that must survive summer drought. There is a5-month summer dormancy stage in the life cycle of Chinese Narcissus (Narcissus tazetta var. chinensis). Understand the mechanism of dormancy could help people regulate its growth and development. Here we analyzed the biological progression of the dormancy and the effects of environmental factors on dormancy relaxation of Chinese Narcissus. The molecular bases of the dormancy release and flower initiation were also studied preliminarily.(1) In the life cycle of Narcissus, we observed its apical meristem (AM) using transmission electron micrograph.The structure of plasmodesmatas (PDs) were various and PDs showed dynamic change. In the natural condition, the most common plasmodesmata (PDs) possessed electron-dense deposits in June and July and the number of such PDs reduced gradually from August. In the active stage, plasmodesmal sphincters are no longer apparent. Simultaneously, amyloplasts also showed dynamic change. The amyloplasts in the bulb apical meristem cells became more and bigger with the dormancy transition from active growth (i.e. from March to late May before harvest). And the largest number and size of amyloplasts appeared during June and July. Amyloplasts began to become fewer and smaller beginning with August. According to the physiological indexes of metabolism and the change of ethylene, we supposed that the endo-dormancy of Chinese Narcissus ended in early August in natural conditions.(2) High-temperature was necessary for bulbs dormant release during storage. Heat accumulation advanced the endo-dormancy ending and it is also benefit for leaf differentiation. After endormancy, low-temperature and ethylene can break eco-dormancy easily and speeded the sprouting.(3) Ethylene treatment advanced dormancy release and leaf differentiation, while1-MCP had the opposite effect. However its negative effect could be reversed by high temperature. Different photoperiod during storage time had little effect on dormancy release.(4) Floral initiation and development occurred during the dormancy stage of Chinese Narcissus showed by the scanning electron microscopic analysis. Two-year bulbs were sampled on different temperature regimes during the storage and planted in the controlled greenhouse. The results showed that high temperature was not only necessary for florescence differentiation in3-year bulbs but also induced2-year bulbs flowering. Enough high-temperature treatment can accelerate floral development and enhance the rate of bolting. Different photoperiod during storage time had little effect on bolting of most bulbs except for some photoperiod sensitive bulbs. Ethylene treatment at different stages had different effects, with accelerating bolting when treated during endodormancy, while less effect on bolting when treated at other stage. The growing span of Chinese Narcissus is usually about six mouths. Ethylene and low temperature treatment during endodormancy could extend the growing stage of Chinese Narcissus.(5) FT gene is the key regulator on both dormancy and flowering. We isolated and characterized NFT1gene, an FT homolog from Chinese Narcissus. The phylogenetic analysis indicated that it belonged to FT-TFL family, FT subfamilies. NFT1had close genetic relationship with FT-like gene in monocotyledonous species such as Triticum aestivum L. Oryza sativa and Phyllostachys meyeri. In vegetative stage the expression of NFT1gene was higher in3years old bulbs than in1or2years old bulbs. In senescence phase, it expressed higher in leaf than in other tissues. During dormancy, NFT gene was up-regulated by high temperature, which implied the expression of NFT1regulated by temperature may be the molecular base for florescence differentiation and endormancy release.(6) In addition, the function of NATG1gene, an AGAMOUS homolog from Chinese Narcissus varieties was also studied. Sequence and expression pattern of NATG1gene exhibited the same in both tested varieties. It expresses only in the reproductive organs. Furthermore, functional analysis by using ectopic tests in Arabidopsis showed that NATGl might be involved in the carpel identity and floral transition The effects of ectopic expression of NATG1mainly include dwarfing, early flowering, losing inflorescence indeterminacy, branch number increasing, and advancing senescence, whereas some of homeotic phenotypes gradually disappeared in higher generation of transgenic plants.In conclusion, we propose our model of dormancy of Chinese Narcissus in nature. The endo-dormancy went through June and July and ended in early August followed by eco-dormancy. The two dormancy stages were defined by an alteration of the symplasm interconnections in meristem cells. The endo-dormancy completion required heating, and eco-dormancy could be released by low temperature or phytohormones easily. Additionally, high temperature accumulation also induced2-year old bulbs flowering. That the expression of NFT1was up-regulated by high temperature suggested that NFT1may be the molecular base for florescence differentiation and endo-dormancy release regulated by temperature.