| The phytohormone ethylene regulates many aspects of plant growth, development, and environmental responses. It's very import to study the biosynthesis of endogenesis of ethylene and ethylene signaling pathway. Our knowledge on the regulation of ethylene synthesis during development of tomato is quite advanced. Much less is known about the regulation of ethylene perception and transduction. Although arabidopsis is clearly the ideal model for analysis of ethylene signal transduction, it can not be the model of choice for climatic fruits.Based on cloning of the partial DNA sequences of LeETRl and LeETR2 ,we transformed tomatoes with antisense LeETRl ~2 .Studying the phenotype of the transgenic plants will help in understanding the physiological function of the receptor gene LeETRl-2 in tomato ethylene signal transduction system. The main results in this paper are as follows:1. A simply and quickly method form screening positive plants from a great number of transgenic tomatoes was developed based on the examination of GUS gene expression in roots.2. Pure transgenic tomato lines were identified by examining GUS expression in pollens. Homozygous line showed all pollens expressed GUS and produced blue color when incubated at 37 "C for 5 h. Heterozygous line showed the segregation ratio of 1:1.Controls plants had no GUS expression in pollens and pollen tubes incubated at 37 C for 5 h and 10 h.3. Northern blot analysis indicated that LeETRl and LeETRl mRNA abundance was decreased in antisense tomato plants.4. Seedlings of both antisense LeETRl transgenic and wild-type plants exposed to ethylene displayed the normal triple response, However, root elongation was strongly inhibited by ethylene, and root hair formation was completely inhibited in transgenic plants. In the absence of ethylene, Hypocotyl and root lengths of the transgenic seedlings were significantly shorter than that of wild type, suggesting a weak constitutive ethylene response in seedlings of antisense LeETRl tomato.5. When exposed to 25 u 1/1 ethylene leaves of WT showed much stronger epinasty than that of antisense LeETRl plants. We arrived a conclusion that transgenic plants were less sensitive to ethylene than WT plants.6. To assess the sensitivity of abscission tissue to ethylene, petiole explants prepared from transgenic lines and WT were exposed to 25 P 1/1 ethylene for 6 d. The time needed for 50% abscission by transgenic(Le?7?2) explants were more than twice the time needed bywild-type.. A similar experiment was performed with flower petiole explants. The delay in flower abscission closely paralleled the results for petiole abscission According to the negative regulation model, decreased LeETRl mRNA abundance should lead to accelerated abscission. We thus infer that the action of ethylene receptors does not always comply with negative regulation model.7. Cellulase is the enzyme typically induced by ethylene. Less cellulase activity were observed in the abscission zones of antisense LeETR2 plants suggesting that signal perception pathway for cellulase expression was also impared in antisense LeETR2 plants.8. The post-harvest physiology of antisense LeETRl and LeETR2 tomato fruits were studied. In antisense LeETRl fruits, Respiratory rate was significantly lower than control. Ethylene production peak appeared lOd after control. Chlorophyll degradation and lycopene biosynthesis was inhibited in transgenic fruits. After 30 days in normal room, transgenic tomatoes eventually developed an orange color but never turned red. During the course of ripening, cellulase and polygalacturonase activity of transgenic fruits were significantly lower than control and the firmness of transgenic fruits declined more slowly. Antisense LeETRl tomato fruits did not show any differences during ripening from control fruits. These results suggest that LeETRl and antisense LeETRl have different function during the ripening of tomato fruits.9. This paper described effect of 1-MCP on the ripening of tomato and expression of ethylene r... |
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