Comparison of Growth Responses to Auxin 1-Naphthaleneacetic Acid and the Ethylene Precursor 1-Aminocyclopropane-1-Carboxilic Acid in Maize Seedling Root

Abstract

Application of 1-naphthaleneacetic acid (NAA) or 1-aminocyclopropane-1-carboxilic acid (ACC) to maize roots growing in hydroponic solution inhibited root elongation, and increased radial growth, but the responses to those treatments differed in degree. Auxin was more effective than ACC as an elongation inhibitor and root swelling promoter. Whereas NAA fully inhibited elongation and maintained swelling over 48 h, ACC inhibited elongation partially (50%) and only promoted swelling for 24 h. It is well-known that auxin, like ACC, promotes ethylene production, but similar levels of ethylene production reached by means of NAA or ACC treatments did not elicit the same response, the response being always stronger to NAA than to ACC. These results suggest that the effect of auxin on root growth is not mediated by ethylene. Elongation and swelling of roots appear to be inversely related: usually a reduction in elongation was accompanied by corresponding swelling. However, these two processes showed different sensitivities to growth regulators. After 24 h treatment with 0.5 μM NAA or 5 μM ACC, root elongation was inhibited by 90% and 53% respectively, but the same treatments promoted swelling by 187% and 140% respectively. Furthermore, 1 μM ACC was shown to promote inhibition of root elongation without affecting swelling. The ethylene antagonist STS (silver thiosulfate) did not affect elongation in control or NAAtreated roots, but increased ethylene production and swelling. These results indicate that longitudinal and radial expansion could be independently controlled.K Ke ey y w wo or rd ds s: : Maize, root, NAA, ACC, auxin, ethylene, STS, root swelling, root elongation.

The Role of Auxin-Ethylene Crosstalk in Orchestrating Primary Root Elongation in Sugar Beet

“…Although auxin is mostly described to inhibit root elongation (Rahman et al, 2007; Ruzicka et al, 2007; Stepanova et al, 2007; Swarup et al, 2007; Alarcón et al, 2012), our results showed that auxin can stimulate root elongation during seedling growth of sugar beet. Evans et al (1994) also found that low concentrations of auxin can stimulate root elongation in Arabidopsis .…”

“…Application of low concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) stimulates root growth while high concentrations inhibit root growth (Abts et al, 2014). It is also known that auxin can inhibit root elongation in many species (e.g., Arabidopsis, Brassica , maize, pea…; Eliasson et al, 1989; Rahman et al, 2007; Ruzicka et al, 2007; Stepanova et al, 2007; Swarup et al, 2007; Alarcón et al, 2012; Polit et al, 2014). In contradiction, it was also previously shown in Arabidopsis that low auxin levels could stimulate root elongation (Evans et al, 1994) which might suggest that auxins can also exert a biphasic response in root growth.…”

Alterations in Auxin Homeostasis Suppress Defects in Cell Wall Function

“…The growth of seedlings in the presence of auxin has been shown to lead to root swelling in a manner independent of ethylene biosynthesis [39] , [40] . This suggests that exogenous auxin decreases the integrity of the cell wall, leading to a loss of growth anisotropy.…”

The OsFBK1 E3 Ligase Subunit Affects Anther and Root Secondary Cell Wall Thickenings by Mediating Turnover of a Cinnamoyl-CoA Reductase

“…This experimental evidence suggests the developmental stages where OsFBK1 might function optimally and corroborate the microarray expression data based on which gene was selected for functional analysis. As auxin is known to play a role in the maintenance of root proliferation (Alarcón et al, 2012), the functions of OsFBK1 could be mediated by this hormone. Although OsFBK1 is a single-copy gene, it shares closest protein sequence homology (.50%) to OsFBK5/ OsEP3.…”