Movement of Indole-3-acetic Acid and Tryptophan-derived Indole-3-acetic Acid from the Endosperm to the Shoot of Zea mays L.

The structures and the concentrations of all of the indolylic compounds that occur in the endosperm of the seeds of corn (Zea mays L.) are known. Thus, it should be possible to determine which, if any, of the indolylic compounds of the endosperm can be transported to the seedling in significant amounts and thus help identify the seed-auxin precursor of Cholodny (1935. Planta 23:289-312) and Skoog (1937. J. Gen. Physiol. 20:311-334). Of interest is the transport of tryptophan, indole-3-acetic acid (IAA), and the esters of IAA, which comprise 95% of the IAA compounds of the seed. We have shown that: (a) IAA can move from the endosperm to the shoot; (b) the rate of movement of IAA from endosperm to shoot is that of simple diffusion; (c) 98% of the transported IAA is converted into compounds other than IAA, or IAA esters, en route; (d) some of the IAA that has moved into the shoot has been esterified; (e) labeled tryptophan applied to the endosperm can be found as labeled IAA in the shoot; and (f) with certain assumptions concerning IAA turnover, the rate of movement of IAA and tryptophan-derived IAA from the endosperm to shoot is inadequate for shoot growth or to maintain IAA levels in the shoot.