Elevation of leaf auxin (indole-3-acetic acid; IAA) levels in intact plants has been consistently found to inhibit leaf expansion whereas excised leaf strips grow faster when treated with IAA. Here we test two hypothetical explanations for this difference in growth sensitivity to IAA by expanding leaf tissues in vivo vs. in vitro. We asked if, in Arabidopsis, IAA - induced growth of excised leaf strips results from the wounding required to excise tissue and/or results from detachment from the plant and thus loss of some shoot or root derived growth controlling factors. We tested the effect of a range of exogenous IAA concentrations on the growth of intact attached, wounded attached, detached intact, detached wounded as well as excised leaf strips. After 24 h, the growth of intact attached, wounded attached and detached intact leaves was inhibited by IAA concentrations as little as 1 μM in some experiments. Growth of detached wounded leaves and leaf strips was induced by IAA concentrations as low as 10 μM. Stress, in the form of high light, increased the growth response to IAA by leaf strips and reduced growth inhibition response by intact detached leaves. Endogenous free IAA content of intact attached leaves and excised leaf strips was found not to change over the course of 24 h. Together these results indicate growth induction of Arabidopsis leaf blade tissue by IAA requires both substantial wounding as well as detachment from the plant and suggests in vivo that IAA induces parallel pathways leading to growth inhibition.
Bibliographical noteFunding Information:
Support for this project by National Institutes of Health (NIH, USA) Grant Number P20 RR016741 from the IDeA Network of Biomedical Research Excellence/Biomedical Research Infrastructure Network (INBRE/BRIN) Program of the National Center for Research Resources is gratefully acknowledged. Research at the University of Minnesota was supported by the National Science Foundation (grants MCB0725149 and IOSPGRP-0923960), the Minnesota Agricultural Experiment Station and the Gordon and Margaret Bailey Endowment for Environmental Horticulture. The publication contents are the responsibility of the authors and conclusions drawn should not be seen as official views of the funding sources.
- Leaf expansion
- Wound response