Regulation of Internodal Extension in Avena Shoots by the Inflorescence, Nodes, Leaves, and Intercalary Meristem

It has been found in recent studies that the inflorescence and nodes (node‐pulvini) are the primary sources for native gibberellins in the Avena shoot, and that GA 3 is the predominant gibberellin in the inflorescence. In the present work, linear growth of next‐to‐last internode is drastically reduced by removal of the inflorescence and last leaf. This growth is completely abolished when the nodes are also excised. It is restored fully by the addition of GA 3 when the nodes are present, and restored only partially when the nodes are deleted. Internodal growth in Avena stem segments with basal node present is also restored by native GA 3 ‐like substances extracted from Avena inflorescences and partially purified by silica gel partition column chromatography. Evidence from these studies, taken in toto , indicates that the inflorescence, nodes, and leaves supply gibberellins, leaves supply substrate, and nodes modulate the gibberellin growth response in next‐to‐last Avena internodes.