PLANT PHYSIOLOGY , Vol 102, Issue 2 417-423, Copyright © 1993 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Ethylene-Mediated Posttranscriptional Regulation in Ripening Avocado (Persea americana) Mesocarp Discs
E. L. Buse and G. G. Laties
Department of Biology, University of California, Los Angeles, Los Angeles, California 90024
Discs of avocado (Persea americana) fruit (15 x 3 mm thick) kept in a
stream of moist air ripen within 72 h. Following cutting, a modest
evolution of wound ethylene that dissipates in 24 h is followed by a burst
of autocatalytic ethylene production associated with a respiratory
climacteric, much as in the intact fruit. Aminoethoxyvinylglycine (AVG), an
inhibitor of ethylene synthesis, and 2,5-norbornadiene (NBD) and Ag+,
inhibitors of ethylene action, inhibit disc ripening, as does
2,4-dichlorophenoxyacetic acid (2,4-D), a synthetic auxin. On the other
hand, none of the foregoing agents except Ag+, at concentrations that delay
or prevent ripening, suppress the induction of four ripening-related genes
encoding cellulase, polygalacturonase (PG), cytochrome P-450 oxidase
(P-450), and ethylene-forming enzyme (EFE, or 1-aminopropane-1-carboxylic
acid oxidase), respectively. Whereas Ag+ fully inhibits the production of
cellulase and PG mRNAs, it has little effect on the induction of EFE and
P-450 mRNAs. Cellulase and PG enzyme activities are absent in extracts of
discs treated with AVG, NBD, or 2,4-D, as are antigenically detectable
cellulase and PG proteins. The strong appearance of ripening-related mRNAs
in discs inhibited from softening by ethylene antagonists suggests
posttranscriptional control by ethylene. Similarly, inhibition of ripening
by 2,4-D without suppression of mRNA induction suggests translational
control. Whether ethylene inhibits transcription or postttranscriptional
events or both depends on its concentration.
