Abstract
At harvest, beechnuts have a very deep dormancy whichlies both in the structures surrounding the embryo andwithin the embryo itself. Covering structures preventembryo germination by interfering with water uptakeand gaseous exchange. To understand the role of thecovering structures and oxygen availability on ABAcatabolism, (+)-[3H] ABA metabolism was studied in isolated embryos as well as in intact seeds. ABAdegradation resulted essentially in oxidative products(PA, DPA). These products were more abundant inisolated embryos than in intact seeds. Theyaccumulated mainly as alkali-nonhydrolyzableconjugates of DPA. A small amount of free andesterified forms were oftenobserved. In isolated embryos a decrease in oxidativeproducts was observed either by lowering the oxygenavailability or by feeding embryos with tetcyclasis(an inhibitor of monooxygenase). In the presence of the covering structures, these oxidative products werereduced in the same manner, indicating that coveringstructures were probably responsible for limiting theoxygen supply to the embryo and for the lowgermination percentage observed in the case of intactseeds.
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