Effects of IAA on oxygen-sensitive growth and on hydroxyproline protein level in cell wall

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Abstract
Indole-3-asscetic acid (IAA) accelerated the incorporation of radioactivity derived from 14C-proline into the SLS-insoluble cell wall fraction only when the sections were exposed to low oxygen concentrations. However, IAA showed no effect on the ratio of hydroxyproline to proline incorporated into the SLS-insoluble fraction in both 20% and 8% O2-treated sections. The amount of hydroxyproline rigidly bound to the cell wall increased with increasing IAA concentration in 8% O2-treated sections, while that of the 20% O2-treated ones decreased with IAA treatment. On the other hand, IAA increased the amount of 14C-labeled hydroxyproline incorporated into the SLS-insoluble fraction of sections treated with cycloheximide, and their elongation was greatly inhibited. Based on the results that O2 and IAA affect the auxin-induced and the oxygen- sensitive growth differently, we suggest that both types of growth may antagonize each other in response to changes in O2 and IAA concentrations, resulting in balanced growth in the cell.