ABSCISIC-ACID BIOSYNTHESIS IN ZEA-MAYS EMBRYOS - INFLUENCE OF TETCYCLACIS AND REGULATION BY OSMOTIC POTENTIAL

Abscisic acid (ABA) accumulation by isolated sweet corn (Zea mays L.) embryos increased when tetcylacis, an inhibitor of ABA catabolism to phaseic acid (PA), was added to the medium (0.1 M Tris, pH 7.0). The induction of plasmolysis by the addition of mannitol also increased the amount of ABA produced. ABA production was not increased by cytorrhysis, which was induced by the non-penetrating osmoticum Aquacide III, or by penetrating solutes, such as ethylene glycol or thiourea. We conclude that ABA production by isolated embryos may be increased only when the osmotic potential of embryos is decreased by plasmolysis and not by cytorrhysis or by penetrating solutes. Osmotic potentials of developing Tx5855 corn embryos were more positive than those of the endosperm from 11 through 19 days after pollination (DAP), but were more negative after 20 DAP. The water potential gradient between the embryo and endosperm in kernels less than 19 DAP may be one factor in controlling embryo production of ABA. The different seed parts were compared for differences in ABA content and biosynthetic capacities with and without tetcyclacis.