Presence of indole-3-acetic acid in chloroplasts ofNicotiana tabacum andPinus sylvestris

Abstract

The compartmentation and metabolism of indole-3-acetic acid (IAA) was examined in protoplasts derived from needles ofPinus sylvestris L., leaves of normal plants ofNicotiana tabacum L., leaves ofN. tabacum plants carrying the T-DNA gene 1 (rG1 plants) and leaves ofN. tabacum plants carrying the T-DNA gene 2 (rG2 plants) by using a rapid cell-fractionation method. In all tissues, 30%–40% of the IAA pool was located in the chloroplast, while the remainder was found in the cytosol. Quantitative analysis of indole-3-ethanol (IEt) showed that in bothPinus andNicotiana the IEt pool was located exclusively in the cytosol. The only plant that contained endogenous indoleacetamide (IAAm) was therG1-mutant ofN. tabacum, expressing theAgrobacterium tumefaciens T-DNA gene 1. Cellular fractionation of protoplasts from this transgenic plant showed that the entire IAAm pool was located in the cytosol. Feeding experiments utilizing [5-³H]tryptophan, [5-³H]IEt, [1′-¹⁴C] and [2′-¹⁴C]IAA demonstrated that the biosynthesis and catabolism of IAA occurred in the cytosol in bothPinus and in the wild type and the different mutants ofNicotiana. Furthermore, the biosynthesis of IAAm in therG1 plants was also shown to be localized in the cytosol.