Endogenous Indole-3-Acetic Acid in the Stem of Tobacco in Relation to Flower Neoformation as Measured by Mass Spectroscopic Assay

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Abstract
The contents of free indole-3-acetic acid (IAA) and alkali-labile, conjugated IAA were measured in relation to a `floral gradient9 present in epidermis and subepidermis tissues of flowering plants of Nicotiana tabacum by capillary gas-chromatographic spectrometric analysis by selected ion monitoring (GC-SIM-MS) using 2,4,5,6,7-penta deutero IA (2H5-IAA) as an internal standard. In floral axes, floral branches and stems with floral branches, free IAA levels (dry weight) were 387, 253, and 417 nanograms, and bound IAA levels were 99, 1089, and 268 nanograms. In vegetative tissue of the first plus second internodes (measured from top), and of the 11th to 13th internodes, free IAA levels were 826 and 500 nanograms, and bound IAA levels were 1421 and 286 nanograms, respectively. Since flower-forming ability of excised cells from the epidermis and subepidermis shows a gradient in an in vitro system, but levels of IAA in these tissues do not, there thus appears to be no correlation between flower-forming ability (in vitro) and endogenous IAA levels (at the time of excision) in tobacco stem tissues.