The possible interaction of ammonium and auxin polar transport on root system architectures in the two ecotypes of Arabidopsis thaliana

Plant growth requires mineral nutrients from soil environment. It is important for plant to develop its root to import mineral nutrient from environment. Both inorganic nitrogen source and plant hormone auxin influence the root system architecture (RSA). Previous study indicated that polar auxin transport is partly involved in ammonium-inhibition of primary root in an Arabidopsis ecotype, Columbia 0 (Col-0); however, the effect of auxin in other ecotypes remains unclear. The purpose of this study is to describe and examine the effect of TIBA, an inhibitor for the auxin polar transport, in ammonium supply-dependent changes of root development. Two Arabidopsis ecotypes, Col-0 and Landsberg erecta 2 (Ler-2), were used due to their different response to ammonium supply. The changes of the RSA in response to ammonium supply on vertical agar medium containing three levels of TIBA and four levels of ammonium were determined in two ecotypes. The primary root length of Ler-2 was markedly shortened by increasing ammonium concentration in the medium, while that of Col-0 was relatively insensitive to ammonium. Conversely, the lateral root length of Ler-2 was increased by ammonium supply. Both primary and lateral root of Col-0 were more sensitive to TIBA than those of Ler-2. ANOVA indicated the significant interaction of TIBA and ammonium in Col-0; however, no interaction in Ler-2. These results suggested the genetic diversity in the interactive effect of auxin and ammonium.