Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Marc Alan Cohn

Abstract

Hydrated, dehulled, dormant seeds of red rice (Oryza sativa L.) were exposed to chemical treatments (nitrite, propionic acid, methyl propionate, propionaldehyde, and n-propanol) that saturate the dormancy-breaking response. Dormancy-breaking chemicals were (a) metabolized (n-propanol and propionate) by embryos in dormant seeds to weak acids; (b) decreased embryo pH; and (c) increased embryo (Fru 2,6-P$\sb2$) prior to dormancy-breaking. Embryo acidification, but not increased embryo (Fru 2,6-P$\sb2$), was associated with the chemical contact interval required for the onset of dormancy-breaking. During chemical contact, embryo (Fru 2,6-P$\sb2$) increased independent of dormancy-breaking and was inversely correlated with the elapsed time to 30% germination. On subsequent transfer to H$\sb2$O, further embryo acidification and increased embryo (Fru 2,6-P$\sb2$) were significantly correlated with visible germination irrespective of the dormancy-breaking chemical employed. These data suggest that dormancy-breaking chemicals lacking a dissociable proton are metabolized to weak acids, leading to embryo acidification that results in dormancy-breaking; increased embryo (Fru 2,6-P$\sb2$) is related to the subsequent germination rate. Embryo acidification may be analogous to that associated with the termination of developmental arrest in other multicellular systems (Brine shrimp and nematodes). In hydrating dormant and nondormant seeds, seed respiration, embryo pH and (Fru 2,6-P$\sb2$) were similar. In phase 2, these parameters diverge as nondormant seeds enter the germination phase. In dormant seeds, embryo (Fru 2,6-P$\sb2$) was transient in phase 2 suggesting the imposition of a block on the germination phase.

Pages

195

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