Effects of fluridone and abscisic acid on lateral root initiation and root elongation of excised tomato roots cultured in vitro

Roots of tomato (Lycopersicon esculentum Mill. cv. Bonny Best) were excised and cultured in the presence of the abscisic acid synthesis inhibitor fluridone, and with concentrations of exogenous abscisic acid ranging from 10(-10) to 10(-4) M to determine the effects of abscisic acid and its synthesis inhibition on the development of lateral roots in in vitro cultured tomato roots. Exogenous abscisic acid inhibited lateral root initiation and emergence at concentrations of 10(-6) M and greater. Fluridone (10(-6) M) enhanced the formation of lateral roots even in the presence of abscisic acid, at all concentrations tested except 10(-4) M. Abscisic acid increased apical distance, and fluridone reduced it up to 10(-5) M abscisic acid. Both fluridone and abscisic acid reduced lateral and primary root lengths. It was concluded the endogenous abscisic acid is probably involved in the regulation of lateral root initiation and root apical dominance, and that abscisic acid may affect lateral root initiation differently than lateral root emergence.