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

The biosynthesis of C-14-IAA from C-14-tryptophan applied to abraded l eaves of Ricinus communis and its subsequent export through the phloem were studied. Phloem sap was collected at intervals from incisions ma de in the stem below the IAA fed leaf. Any upward movement of label th rough the phloem or downward movement of phloem mobile compounds from leaves above the treated one were restricted by bark-ringing the plant s. TLC and HPLC analyses of the collected sap indicate that some conve rsion of C-14-tryptophan to C-14-IAA had occurred. Subsequent GC-MS an alysis of the HPLC purified samples of phloem sap revealed high levels of endogenous IAA transported from the fed leaf. The high ratio of un labelled/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 an d exported to developing sink tissues with the flow of photoassimilate s in the phloem.