Sites of gibberellin biosynthesis in pea seedlings.

Potential sites of gibberellin biosynthesis in 10-day-old ;Alaska' pea (Pisum sativum L.) seedlings were investigated using a cell-free ezyme system capable of incorporating [(14)C]-mevalonic acid into ent-kaurene. In peas, ent-kaurene is assumed to be a committed intermediate in the gibberellin biosynthetic pathway. Comparative results from enzyme assays using extracts from shoot tips, leaf blades, internodes, and root tips indicate that the highest capacity for ent-kaurene (and presumably gibberellin) synthesis is in those tissues with the greatest potential for growth. The highest rates were obtained with extracts prepared from the fifth (youngest) internode, the fourth (youngest) expanded leaf, and the shoot tip itself. This report represents the first direct evidence that the enzymes responsible for early stages in gibberellin biosynthesis occur in internode tissues with potential for rapid elongation.