Root growth in Arabidopsis requires gibberellin/DELLA signalling in the endodermis
Gibberellins (GAs) are key regulators of plant growth and development. They promote growth by targeting the degradation of DELLA repressor proteins; however, their site of action at the cellular, tissue or organ levels remains unknown. To map the site of GA action in regulating root growth, we expressed gai, a non-degradable, mutant DELLA protein, in selected root tissues. Root growth was retarded specifically when gai was expressed in endodermal cells. Our results demonstrate that the endodermis represents the primary GA-responsive tissue regulating organ growth and that endodermal cell expansion is rate-limiting for elongation of other tissues and therefore of the root as a whole.
Democrat Barack Obama's appeal to  centrist voters has further opened the door to Republican claims his message of change only applies to the positions he has taken in the past.
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