QUANTITATIVE STRUCTURE-ACTIVITY-RELATIONSHIPS FOR N-(INDOL-3-YLACETYL)AMINO ACIDS USED AS SOURCES OF AUXIN IN PLANT-TISSUE CULTURE

The methods of quantitative structure-activity relationship (QSAR) ana lysis were applied to two sets of N-(indol-3-ylacetyl)amino acids test ed in vitro as promoters of unorganized callus growth in cultures deri ved from Solanum nigrum L. and from soybean (Glycine max L.). Two type s of statistical models were developed describing molecular structure: (a) by molecular connectivity indices or (b) by experimentally determ ined biochemical constants. The parameter structure of those models in dicated that the mode of action of the indole-3-acetic acid (IAA) conj ugates is similar in both plant systems. Growth-promoting activities d ecreased with molecular size and with increasing involvement of the am ino acid C-alpha and C-beta in branched or cyclic structures. This was more clearly visible when molecular connectivity indices were employe d as descriptor variables. The biochemical constants which most accura tely describe the auxin-like effect of N-(IAA)amino acids are lipophil icity and resistance to degradation by peroxidase. This suggests that biological activity mostly depends on uptake and metabolic stability. The latter includes hydrolysis to free IAA, but the models do not supp ort the popular hypothesis that this is the only rate-determining step .