Effects of Trifluralin on the IAA and ABA Levels in Growing Maize Roots

Abstract

The action of the herbicide trifluralin (TF = α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) on the growth of roots of Zea mays cv. LG 11 was investigated. Elongation, radial extension, and free levels of IAA and ABA were measured for roots treated with TF (5 μM :1 min immersion). After TF application, elongation of fast growing (FG) roots was slowed down rapidly and their diameter strongly increased. However, the elongation rate of slow growing (SG) roots was unaffected over 12 hours by TF. Such difference in reactivity to TF seemed not to be linked to its uptake by the roots since amounts of 14C-TF in the elongation zone were similar for the two growth classes of roots. GC-MS quantification of free ABA and IAA in treated roots indicated that the ABA level rapidly increases (within 2 h) after TF treatment whereas the IAA level changes slightly a few hours later. Such modifications are larger in FG than in SG roots. Eight hours after TF application, IAA and ABA levels recover to their initial ratio. Possible implications of these two hormones in TF action are discussed.