Effects of IAA and four IAA conjugates on morphogenesis and callus growth from tomato leaf discs

Abstract

The effects of indole-3-acetic acid (IAA) and four IAA conjugates, indoleacetylalanine (IAAla), indoleacetylaspartic acid (IAAsp), indoleacetylglycine (IAGly), and indoleacetylphenylalanine (IAPhe), on growth and morphogenesis in tomato leaf discs in vitro were examined. Free IAA stimulated root initiation in the absence of cytokinin and stimulated callus growth in the presence of 0.89 μM benzylaminopurine (BAP). Free IAA also inhibited shoot initiation obtained with 8.9 μM BAP. The activities of the IAA conjugates depended on the conjugating amino acid, the concentration of the conjugate, and the response being measured. IAAsp had little or no activity in promoting root initiation or callus growth or in inhibiting shoots, while IAPhe was similarly inactive except at the highest concentration tested (100 μM). IAAla and IAGly were both very active in inhibiting shoots and promoting callus growth, but were much less active in stimulating rooting, except at 100 μM, at which concentration they were as effective as free IAA. Thin-layer chromatography of the IAA conjugates revealed that IAAla, IAGly and IAPhe were largely stable to autoclaving, but that IAAsp underwent some hydrolysis to products identical with free IAA and aspartic acid. Pretreatment of seedlings with IAA, IAAla or IAGly altered the subsequent shoot initiation response from leaf discs on media with and without IAA.