Pea (Pisum sativum L.) fruit naturally contain the auxins, indole-3-acetic
acid (IAA) and 4-chloroindole-3-acetic acid (4-Cl-IAA). However, only 4-Cl-
IAA can substitute for the seeds in maintaining pea fruit growth in planta.
The importance of the substituent at the 4-position of the indole ring was
tested by comparing the molecular properties of 4-X-IAA (X = H, Me, Et, F,
or Cl) and their effect on the elongation of pea pericarps in planta. Stru
cture-activity is discussed in terms of structural data derived from X-ray
analysis, computed conformations in solution, semiempirical shape and bulk
parameters, and experimentally determined lipophilicities and NH acidities.
The size of the 4-substituent, and its lipophilicity are associated with g
rowth promoting activity of pea pericarp, while there was no obvious relati
onship with electromeric effects.