Comparative Effects of Ethylene and Cyanide on Respiration, Polysome Prevalence, and Gene Expression in Carrot Roots

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Abstract
Treatment of carrot roots (Daucus carota L.) with 10 microliters per liter ethylene in O2 evokes a three- to four-fold increase in polysome prevalence and associated poly(A)+ RNA. The increase in polysome prevalence is attended by a similar change in CO2 evolution. The increase in polysomal poly(A)+ mRNA constitutes primarily a generic increase in constitutive mRNAs as assayed by in vitro translation. However, changes in the relative abundance of several in vitro translatable ethylene specific mRNAs do occur. Cyanide, at concentrations which inhibit cytochrome oxidase, initiates a respiratory rise very similar in kinetics and magnitude to that evoked by ethylene. Moreover, the combined treatment with cyanide and ethylene evokes a respiratory response resembling that caused by ethylene or cyanide alone. Nevertheless, cyanide, in the presence of ethylene, significantly inhibits the increase in polysome prevalence and new gene expression associated with ethylene treatment of carrot roots. Separation of in vitro translation products by one-dimensional and two-dimensional gel electrophoresis shows that several new in vitro translation products appear in cyanide-treated carrots different from those evoked by ethylene. Engagement of the less energy efficient alternative electron transport path by cyanide may be responsible for inhibition of the normal ethylene associated increase in polysome prevalence and new gene expression. The implications of these results on regulation of respiratory metabolism are discussed and compared with the results for similar experiments with avocado fruit (Tucker and Laties 1984 Plant Physiol 74: 307-315) in which cyanide does not inhibit an ethylene educed increase in polysome prevalence and change in gene expression.