Transport of Indole-3-Butyric Acid and Indole-3-Acetic Acid in Arabidopsis Hypocotyls Using Stable Isotope Labeling      

Abstract

The polar transport of the natural auxins indole-3-butyric acid (IBA) and indole-3-acetic acid (IAA) has been described in Arabidopsis (Arabidopsis thaliana) hypocotyls using radioactive tracers. Because radioactive assays alone cannot distinguish IBA from its metabolites, the detected transport from applied [ ]IAA was found in the basal end. Our results demonstrate that the polar transport of IBA is much lower than IAA in Arabidopsis hypocotyls, and the transport mechanism is distinct from IAA transport. These experiments also establish a method for quantifying the movement of small molecules in plants using stable isotope labeling.Indole-3-acetic acid (IAA), the most abundant form of the plant hormone auxin, is critical for plant growth and development. IAA levels are regulated in plants by multiple means, including biosynthesis of IAA through both Trp-dependent and Trp-independent pathways, conjugation of IAA via ester or amide bonds that can be hydrolyzed to release free IAA, polar transport of IAA over long distances, and degradation of IAA (for review, see Woodward and Bartel, 2005;Seidel et al.,

A Critical View on ABC Transporters and Their Interacting Partners in Auxin Transport

“…Independent IAA and IBA transport catalysts are also supported by the finding that neither NPA nor the competitive auxin inhibitor, TIBA (2,3,5-triiodobenzoic acid), blocks IBA transport (Rashotte et al 2003, Liu et al 2012. Genetic approaches in Arabidopsis support the idea that IBA efflux from root cells is catalyzed by at least two members of the PLEIOTROPIC DRUG RESISTANCE (PDR) subclade of the ABCG family of ABC transporters (Borghi et al 2015): loss of ABCG36/PDR8/PEN3 Bartel 2009, Lu et al 2015) and ABCG37/PDR9/PIS1 , Ruzicka et al 2010 increases sensitivity to IBA, but not IAA.…”

“…Two independent studies support this concept (Rashotte et al 2003. Liu et al 2012; however, only one study verified the identity of the transported radiotracer as IBA (Liu et al 2012).…”

“…Two independent studies support this concept (Rashotte et al 2003. Liu et al 2012; however, only one study verified the identity of the transported radiotracer as IBA (Liu et al 2012). In contrast, Ruzicka et al (2010) came to the conclusion that most of the applied IBA was converted to IAA.…”

1,3-di(benzo[d]oxazol-5-yl)urea acts as either adventitious rooting adjuvant or xylogenesis enhancer in carob and pine microcuttings depending on the presence/absence of exogenous indole-3-butyric acid

“…The simultaneous presence of unusual chemicals, e.g., 5-BDPU or 6-BDPU, plus auxin, has been described to promote adventitious rooting, reducing the disadvantages of a treatment with auxin alone (Ricci et al 2006;Brunoni et al 2014). To enlarge the action spectrum of these urea derivatives to commercial and/or environmental important species, but also to extend the knowledge on their morphogenic roles, they were presently used in in vitro micropropagated cuttings of Ceratonia siliqua L. Indole-3-butyric acid, i.e., the endogenous precursor of IAA (Liu et al 2012, and references therein), is useful in many culture systems to improve AR formation when applied exogenously, alone or in combination of a little amount of cytokinin. By the use of this hormone, present results showed that the simultaneous supplementation of IBA with 5-BDPU enhanced carob adventitious rooting.…”

“…In this plant and culture system, the gene expression occurs in both AR initiating cells and xylogenesis initiating cells, and is independent of exogenous IBA (Liu et al 2012;Della Rovere et al 2015). There is no information about a possible enhancing effect of 5-BDPU, and other similar urea derivatives, on the expression/activity of this auxin influx carrier.…”