鎘離子對四季豆白化下胚軸乙烯生合成之影響

Effect of Cd[fec7] Treatment on Ethylene Biosynthesis in Etiolated Snap Bean Hypocotyls

本試驗以四季豆白化下胚軸為材料，探討鎘毒害對其乙烯生合成之影響。以硫酸鎘處理四季豆白化下胚軸，會誘發合成乙烯，乙烯釋放率隨處理濃度增加而上升，且在處理後10-15小時達到高峰。此種乙烯主要是由鎘離子所促成，而非硫酸根離子。鎘離子處理後，在下胚軸內l-aminocyclopropane-1-carboxylic acid（ACC）含量會增加，及添加aminoethoxyvinyl glycine（ACC合成酵素之抑制劑）及cycloheximide（蛋白質合成抑制劑）時則乙烯之合成受抑制，此結果顯示鎘離子促進下胚軸乙烯合成是誘發ACC合成酵素所致。另外，鎘離子會抑制ACC轉化為乙烯及乙烯形成酵素（ethylene-forming enzyme, EFE）活性。故鎘離子對四季豆下胚軸乙烯合成之影響為誘發ACC合成酵素，抑制EFE活性，整體而言則促進乙烯之合成。

The effect of cadmium toxcity on the production of ethylene in etiolated snap bean (Phaseo/us vu/garis L.) hypocotyls was investigated. Etiolated snap bean hypocotyls normally produced very little ethylene, but following a cadmium ion stress, an abrupt and temporal pattern of stress ethylene production was induced, and increasing concentration of cadmium ion from 0.048 to 0.384mM progressively enhanced the production of ethylene. Following incubation, the rate of ethylene production reached a maximum during 10-15 hr. The stress ethylene was induced by cadmium ion, not by sulfate. Direct evidences showed that cadmium ion induced formation ACC and on the other hand, reduced the activity of ethylene-forming enzyme (EFE). Cycloheximide (a protein synthesis inh血tor) effectively blocked the ethylene production,·suggesting that cadmium ion stress induced de nova synthesis of ACC synthesis. Meanwhile, amino-ethoxyvinylglycine (AVG) inh心ted the ethylene formation, also suggested ACC synthase as the limiting factor .