| The sales volume of cut chrysanthemum has been over 60% in the world market of cut flowers since 1950s, and the demands of the cut chrysanthemum have increased drastically all over the world. Therefore, the annual supply and circulation of the cut chrysanthemum are of great importance. A.K.Kader, an expert in post-harvest technology in California State University, stated that the loss of the horticulture crops during the post-harvest process was 5%-25% in developed countries other than 20%-50% in developing countries. As this may be considered, the researches on quality preserving and senescence-preventing technologies have been caused widely spread recognition. The wilting of the leaves and flowers, the fading and yellowing of the leaves, unfolding of the flowers, and shortening vase life are the crucial problems during the post-harvest period of the cut chrysanthemum, but the occurrence of early senescence is the most important factor which affects the quality of the cut chrysanthemum. The ordinary freshness-preserving technology of cut flowers is to alter the phytohormone levels in the flowers by the use of exogenous hormone. Applying exogenous 6-BA, Guo Weiming et al. maintained the water content of the cut chrysanthemum effectively, and enhanced the synthesis of the chlorophyll and the soluble proteins in it. The quality and the life span of the cut chrysanthemum were improved remarkably, but the early senescence was still unresolved to a more extensive extent. Therefore, the post-harvest technologies and the improvment of the genetic natures should be considered as the most important quality-preserving measures of the cut flowers. Researches on improving the post-harvest quality of cut flowers focused mostly on the traditional breeding, domesticating, and managing ofthe growth. However, researches on using of the biotechnology to control the post-harvest characteristics are very limited contrasting the increasingly higher quality standards in the world market of cut flowers. There are several difficulties in the traditional breeding methods, such as the great uncertainty, the highly difficult hybridization, and the longer breeding periods. The transgenic methods have the advantages of overcoming the disturbance of heredity, oriented transferring of fine target genes, stabilizing the natures of the progenies, and shortening the breeding periods. Consequently, it is necessary and reasonable to reconstruct novel cut chrysanthemum plants with foreign genes by the genetic engineering methods.The results of Guo Weiming et al. indicated that the rising of endogenous ABA and IAA in the aging leaves of the cut chrysanthemum probably induced the production of ethylene in the leaves, which might be the possible reason of the early wilt. The chrysanthemum leaves treated with ABA enhanced the amount of ethylene 8-fold, however, treatments with ABA and then with 6-BA resulted in the antagonism of ethylene producing, and high level of endogenous CTK prevented the senescence of the cut chrysanthemum. Transferring the SAG n -ipt, the autoregulated gene of inhibiting leaf senescence, into the plants is the possible way of resolving the problems of early senescence of the cut chrysanthemum. The autoregulator was controlled by the senescence-induced promoter of SAG 12 , and it caused the excessive and specific expression of CTK in a short aging time and postponed the aging process of the leaves. Gan et al. transfered this autoregulator into the tobacco plants and caused the delayed of the senescence and the pohtosynthetis deterioration in the leaves, but the abnormal development of the leaves did not occur.By activating the ACC synthase, free IAA induces the producing of ETH which is involved in the process of coordinating senescence. Saradhi discovered that IAA could reverse the delayed senescence of the cut chrysanthemum caused by Coda, and the effect of BA could be inhibited by IAA. The iaaL gene is from Pseudomonas.syringae subsp. Savastanoi and encodes the iaaL synthase. IaaL synthase catalyses the conjugatio... |
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