SEED DORMANCY IN RED RICE .10. A C-13-NMR STUDY OF THE METABOLISM OF DORMANCY-BREAKING CHEMICALS

The metabolism of organic dormancy-breaking chemicals is poorly define d and may provide clues to their mode of action. Therefore, hydrated, dormant seeds of red rice (Oryza sativa L.) were exposed to dormancy-b reaking treatments of propionate-2-C-13 (22 mM) or propanol-1-C-13 (75 mM) for 24 h at 30 degrees C. Embryo extracts were analyzed by C-13-n uclear magnetic resonance spectroscopy. Metabolism of propionate and p ropanol to 3-hydroxypropionate, an intermediate of the modified beta-o xidation pathway, was detected after 2 and 4 h, respectively. This occ urred prior to the onset of dormancy-breaking which required 12 h of c hemical exposure. Accumulation of 3-hydroxypropionate was rapid and li near in the embryos of propionate-treated seeds. In the embryos of pro panol-treated seeds, the level of 3-hydroxypropionate reached a platea u at 4 h. Following 24 h of contact with propionate, labeled citrate w as detected in the embryos. The decrease in tissue pH associated with the dormancy-breaking process was Fully accounted for by direct acid u ptake and metabolic production of 3-hydroxypropionate.