Abstract
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.
Highlights
The gaseous plant hormone ethylene has been shown to regulate a myriad of physiological and developmental processes including germination, root growth and root hair formation, leaf expansion, leaf and flower senescence, abscission, fruit ripening, nodulation, and the response to numerous stresses (Burg and Burg, 1962; Abeles et al, 1992; Vandenbussche et al, 2012)
A small-scale experiment was carried out to determine whether the inhibitory effect of ACC on rosette growth is influenced by the presence of sucrose (Figure S1)
Since the discovery of ACC as a biosynthetic precursor of the plant hormone ethylene about 4 decades ago (Adams and Yang, 1979), most studies were focused on identifying the mechanisms controlling ethylene synthesis and its subsequent in vivo responses
Summary
The gaseous plant hormone ethylene has been shown to regulate a myriad of physiological and developmental processes including germination, root growth and root hair formation, leaf expansion, leaf and flower senescence, abscission, fruit ripening, nodulation, and the response to numerous stresses (Burg and Burg, 1962; Abeles et al, 1992; Vandenbussche et al, 2012). The rate-limiting step in the biosynthesis of ethylene is the conversion of SAM to ACC, catalyzed by the enzyme ACC synthase (ACS) (Boller et al, 1979; Yang and Hoffman, 1984). The transcription of ACS genes is highly regulated during plant development and in response to a wide variety of developmental, hormonal, and environmental stimuli (Liang et al, 1992; Van Der Straeten et al, 1992; Tsuchisaka and Theologis, 2004). ACS is the major rate-limiting enzyme in ACC-Specific Regulation of Vegetative Growth ethylene biosynthesis, under certain conditions, for example, during fruit ripening, ACO can become rate-limiting (Barry et al, 1996; Van De Poel et al, 2012). The levels of ACC are regulated at the level of ACS and ACO activity, but are dependent on conjugation and deamination of ACC (Amrhein et al, 1981; Martin et al, 1995; Glick et al, 1998; Mcdonnell et al, 2009)
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