The plant hormone ethylene plays a pivotal role in virtually every aspect of plant development, including vegetative growth, fruit ripening, senescence, and abscission. Moreover, it acts as a primary defense signal during plant stress. Being a volatile, its immediate biosynthetic precursor, 1-aminocyclopropane-1-carboxylic acid, ACC, is generally employed as a tool to provoke ethylene responses. However, several reports propose a role for ACC in parallel or independently of ethylene signaling. In this study, pharmacological experiments with ethylene biosynthesis and signaling inhibitors, 2-aminoisobutyric acid and 1-methylcyclopropene, as well as mutant analyses demonstrate ACC-specific but ethylene-independent growth responses in both dark- and light-grown Arabidopsis seedlings. Detection of ethylene emanation in ethylene-deficient seedlings by means of laser-based photoacoustic spectroscopy further supports a signaling role for ACC. In view of these results, future studies employing ACC as a proxy for ethylene should consider ethylene-independent effects as well. The use of multiple knockout lines of ethylene biosynthesis genes will aid in the elucidation of the physiological roles of ACC as a signaling molecule in addition to its function as an ethylene precursor.
Keywords: 1-aminocyclopropane-1-carboxylic acid; ethylene signaling; root growth; rosette growth; triple response; vegetative growth.
Copyright © 2019 Vanderstraeten, Depaepe, Bertrand and Van Der Straeten.