THE BIOSYNTHESIS AND TRANSLOCATION OF C-14 IAA IN RICINUS-COMMUNIS

The biosynthesis of C-14-IAA from C-14-tryptophan applied to abraded leaves of Ricinus communis and its subsequent export through the phloem were studied. Phloem sap was collected at intervals from incisions made in the stem below the IAA fed leaf. Any upward movement of label through the phloem or downward movement of phloem mobile compounds from leaves above the treated one were restricted by bark-ringing the plants. TLC and HPLC analyses of the collected sap indicate that some conversion of C-14-tryptophan to C-14-IAA had occurred. Subsequent GC-MS analysis of the HPLC purified samples of phloem sap revealed high levels of endogenous IAA transported from the fed leaf. The high ratio of unlabelled/labelled IAA in the phloem sap makes unequivocal confirmation by GC-MS of the predicted biosynthesis of C-14-IAA impossible. It is postulated that IAA is synthesised from tryptophan in mature leaves and exported to developing sink tissues with the flow of photoassimilates in the phloem.