N-(INDOL-3-YLACETYL)AMINO ACIDS AS SOURCES OF AUXIN IN PLANT-TISSUE CULTURE

N-(Indol-3-ylacetyl) derivatives (IAA conjugates) of aliphatic amino a cids with a two- to six-carbon backbone including alpha-L-amino acids, omega-amino acids, and the alpha,omega-diamino acids ornithine and ly sine were prepared, chemically characterized, and tested as sources of auxin in plant tissue culture. Stimulation of unorganized growth in S olanum nigrum L. callus and callus induction and developmental effects in tomato (Lycopersicon esculentum Mill. cv. Marglobe) hypocotyl expl ants were studied systematically. Relative auxin activities were estim ated by comparing physiologically equivalent concentrations, in the op timal and suboptimal range, of the individual IAA conjugates. While th e growth-promoting properties of some of the conjugates were species-d ependent, those containing straight-chain two- to four-carbon alpha-L- amino acid moieties were generally up to 100 times more active than th ose of their five- to six-carbon homologues. Branching of the amino ac id backbone at C-beta (norvaline vs. valine and norleucine vs. isoleuc ine) and C-gamma (norleucine vs. leucine) had a minor effect, but subs titution of H-alpha by a methyl group (alpha-amino-L-butyric vs. alpha -aminoisobutyric acids) almost completely blocked growth-promoting act ivity. IAA conjugates of omega-amino acids were, in most cases, nearly as active as those of their alpha-amino-L-isomers. Among the conjugat es of alpha,omega-diamino acids N(delta)-(IAA) ornithine was less acti ve than N(epsilon)-(IAA)lysine. The activity of N(alpha)-(IAA)lysine w as less than for the epsilon-(IAA) isomer, and that of N(alpha),N(epsi lon)-(IAA)2-lysine was different in tomato and Solanum nigrum. The L-a lanine and epsilon-lysine conjugates were also found to be useful for induction and development of Oenothera leaf callus and in tomato cell- suspension culture, two systems which require highly active sources of auxin.