MUTATIONS IN ARABIDOPSIS-THALIANA GENES INVOLVED IN THE TRYPTOPHAN BIOSYNTHESIS PATHWAY AFFECT ROOT WAVING ON TILTED AGAR SURFACES

Arabidopsis thaliana roots grow in a wavy pattern upon a slanted surfa ce. A novel mutation in the anthranilate synthase alpha 1 (ASA1) gene, named trp5-2(wvc1), and mutations in the tryptophan synthase alpha an d beta 1 genes (trp3-1 and trp2-1, respectively) confer a compressed r oot wave phenotype on tilted agar surfaces. When trp5-2(wvc1) seedling s are grown on media supplemented with anthranilate metabolites, their roots wave like wild type. Genetic and pharmacological experiments ar gue that the compressed root wave phenotypes of trp5-2(wvc1), trp2-1 a nd trp3-1 seedlings are not due to reduced IAA biosynthetic potential, but rather to a deficiency in L-tryptophan (L-Trp), or in a L-Trp der ivative. Although the roots of 7-day-old seedlings possess higher conc entrations of free L-Trp than the shoot as a whole, trp5-2(wvc1) mutan ts show no detectable alteration in L-Trp levels in either tissue type , suggesting that a very localized shortage of L-Trp, or of a L-Trp-de rived compound, is responsible for the observed phenotype.