Uptake and Fate of Ethephon ([2-Chloroethyl]phosphonic Acid) in Dormant Weed Seeds

Although ethephon ([2-chloroethyl]phosphonic acid) is often used as a form of liquid ethylene in studies of seed germination, it is not known if ethylene evolved from ethephon in the seed is sufficient to elicit the desired response and/or if ethephon has a regulatory action that alone accounts for the response. For these reasons we studied the uptake and fate of [1,2-(14)C]ethephon in dormant seeds of Avena fatua, Sinapis arvensis, Thlaspi arvense, and Chenopodium album. The radioactivity within the seeds was separated into a labile carbon-labeled ethephon/ethylene fraction (64-87%) and, following extraction in methanol-chloroform-water (12:5:3), into fractions associated with insoluble (12-29%) and soluble (3-8%) seed constituents. The radioactivity associated with seed constituents was reduced 5 to 75% by hot alkaline hydrolysis (2.5 n KOH, 70 degrees C for 1 hour). Although a small portion of the ethephon (or metabolite of ethephon/ethylene) taken up by the seeds is tightly bound to the tissues, our results indicate that, at the appropriate external concentrations of ethephon, the amount of ethylene evolved from ethephon within the seeds is sufficient to produce the desired ethylene mediated responses. However, factors affecting the decomposition of ethephon must be considered in the decision as to whether to use ethephon as a liquid supply of ethylene.