ABSTRACT
Abscisic acid (ABA) is a carotenoid-derived molecule that was rst isolated from cotton plants and named abscisin (Liu and Carnsdagger 1961; Ohkuma et al. 1963) and from birch leaves and named dormin (Eagles and Wareing 1963). e name of this endogenous growth inhibitor in plants later became ABA (Addicott et al. 1968), derived from its initially assumed role in abscission of fruit and leaves. But this phytohormone also plays a major role in the response to stress and in netuning growth and development (Lumba et al. 2010). ABA controls stomatal aperture, and based on its involvement in germination, bud growth, and lateral root outgrowth, it is also regarded as a dormancy hormone (Rohde et al. 2002; De Smet et al. 2006; Holdsworth et al. 2008). ABA does not appear to play a major role in organ development but rather in regulating the transitions between developmental stages, interacting with various other hormones to regulate plant growth and development (De Smet et al. 2003; Achard et al. 2006; Zhang et al. 2009, 2010). Here, we will describe the physiology and functions of ABA in roots, with a particular emphasis on its role in root growth, root branching, and root-shoot communication.
