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J. WARREN WILSON, P. M. WARREN WILSON, E. S. WALKER, P. J. HALL, IAA Amino Acid Conjugates Induce Differentiation of Tracheary Strands in Lettuce Pith Explants, Annals of Botany, Volume 69, Issue 2, February 1992, Pages 135–144, https://doi.org/10.1093/oxfordjournals.aob.a088318
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Abstract
Each of four amino acid conjugates of IAA was able to replace the IAA requirement for xylogenesis in lettuce pith explants, when supplied at concentrations ten to 100 times those optimal for IAA. Tracheary development induced by these conjugates tended to be slightly slower and less in amount than with IAA, and the tracheary strands shorter and less regular. Responses differed somewhat among the four conjugates: IAA-D, L-aspartate gave development most like that with free IAA, and IAA-D, L-phenylalanine often yielded the weakest tracheary development, while responses to IAA-L-alanine and IAA-glycine were intermediate. The results are interpreted in terms of the ‘bound’ IAA conjugates diffusing into the pith explants and becoming xylogenic only on hydrolysis to ‘free’ IAA. As tracheary strand formation is believed to result from IAA fluxes, it seems that the free IAA also moved through the discs, presumably towards the surfaces where it degrades rapidly. Tracheary strand formation in these explants can be compared with vascular strand formation in the normal shoot tip, where IAA conjugates (auxin ‘precursors’) move acropetally and are hydrolysed to free IAA especially in the young leaf primordia, we suggest, yielding local sources of IAA which may contribute both to the phyllotactic spacing of primordia and, moving basipetally, to the definition of the auxin pathways that develop as procambial strands behind individual leaf primordia.
