Biosynthesis and conjugation of indole‐3‐acetic acid in tobacco crown gall

Abstract

The in vivo metabolism of [3H]‐tryptophan (TRP), [14C]‐indole‐3‐acetaldoxime (IAOX), and [14C]‐indole‐3‐acetic acid (IAA) has been studied in non‐transformed and Agrobacterium tumefaciens T 37 transformed cells of Nicotiana tabacum L. cv. White Burley. Metabolites were analyzed by thin‐layer chromatography (TLC) and high pressure liquid chromatography (HPLC). TRP was converted to IAOX and indole‐3‐ethanol (IEOH) in both cell types, while indole‐3‐acetamide (IAAM) occurred exclusively in transformed cells. The formation of IEOH was higher in transformed cells. IAOX was metabolized to IEOH and IAA in both tissues, whereas only in transformed cells some conversion to IAAM occurred. Furthermore, the conversion of the aldoxime to IAA was higher in transformed cells. Labelled IAA became rapidly conjugated to indole‐3‐acetylaspartic acid (IAAsp) in both cell types, the transformed cells showing a 100% increased uptake of IAA. In vitro incubations of [14C]‐IAOX with desalted extracts from transformed cells showed no significant enzymatic conversion to IAAM, whereas in the presence of flavin adenine dinucleotide (FAD) some chemical conversion was observed. The present results suggest that in an established line of transformed cells the integration of the T‐DNA leads to a permanent transcription of its own auxin genes. Furthermore, the in vivo studies suggest that the host cell's capacity for IAA biosynthesis and conjugation may be altered quantitatively. The potential role of IAOX in both transformed and non‐transformed cells is discussed.