AUXIN CONTROL OF PHOTOASSIMILATE TRANSPORT TO AND WITHIN DEVELOPING GRAINS OF WHEAT

Rates of C-14-labelled photoassimilate and dry matter import into deve loping grains of wheat (Triticum turgidum cv. Franshawi) were enhanced by indolyl-3-acetic acid (IAA) applied in an agar gel infused into th e flag internodal lacunae of intact plants or as an aqueous solution t o detached, aseptically-cultured ears. Enhancement of assimilate impor t occurred in the absence of any changes in the net rates of flag leaf and ear photosynthesis and the relative rates of C-14-labelled photoa ssimilate export from the flag leaves, Sucrose concentrations and osmo lalities of saps collected from the rachis phloem and bulk maternal ti ssues of the grain crease region also were unaffected. However, both t he sucrose concentration and osmolality of the endosperm cavity sap wa s elevated by IAA. The sucrose concentration of the bulk filial sap in creased without any detectable change in sap osmolality. Auxin stimula ted accumulation rates of [C-14]sucrose from the endosperm cavity of d etached intact grain and by filial tissue slices enriched in the cells of the modified aleurone/subaleurone layers. Auxin-enhanced [C-14]suc rose accumulation was abolished by para-chloromercuribenzenesulfonic a cid and erythrosin B. We conclude that IAA stimulates photoassimilate transport to and within developing wheat grains by a primary action on the membrane exchange of solutes to and from the endosperm cavity.