Over decades, the so-called growth regulator or auxin herbicides had resisted all efforts to elucidate their molecular interactions and the biochemical and physiological basis of their phytotoxicity.1-3 The identification and crystal structure analysis of receptors for auxin perception4-8 and the discovery of a new hormone interaction in signalling between auxin, ethylene and the up-regulation of 9-cis-epoxycarotenoid dioxygenase (NCED) in abscisic acid (ABA) biosynthesis,9 leading to ABA accumulation,3 are long steps towards understanding of auxin herbicide action in dicot plants.