Myo-Inositol Esters of Indole-3-acetic Acid as Seed Auxin Precursors of Zea mays L.

Abstract

Indole-3-acetyl-myo-inositol esters constitute 30% of the low molecular weight derivatives of IAA in seeds of Z. mays. [14C]Indole-3-acetyl-myo-inositol was applied to a cut in the endosperm of the seed and found to be transported from endosperm to shoot at 400 times the rate of transport of free IAA. The rate of transport of indole-3-acetyl-myo-inositol from endosperm to shoot was 6.3 pmol/shoot per h and thus adequate to serve as the seed auxin precursor for the free IAA diffusing downward from the shoot tip. Indole-3-acetyl-myo-inositol is the 1st seed auxin precursor to be identified. Application of either [14C]IAA or 14C-indole-3-acetyl-myo-inositol ester to the endosperm results in both free and esterified [14C]IAA in the seedling shoot. Esterification of free IAA and hydrolysis of indole-3-acetyl-myo-inositol occurred in the shoot and not the endosperm yielding ratios of ester to free IAA which approximate the ratios of ester to free IAA normally found in corn shoot tissue. Esterified IAA and free IAA were interconvertible in the growing shoot. Since free IAA may be limiting for plant growth, knowledge that the free hormone is in equilibrium with its conjugates suggests new methods for the control of plant growth.