Metabolic Changes in Indian Ricegrass Seeds in Relation to Coat‐imposed and Embryonal Dormancy1

Abstract

AbstractIndian ricegrass, Oryzopsis hymenoides (Roem & Shult.) Ricker, seeds are dormant at harvest and show a coat‐imposed as well as an embryo dormancy. In this investigation we report on the relationship of the two types of dormancy to changes in certain enzymes implicated in seed germination and seedling growth. Scarification with concentrated sulfuric acid followed by hormonal treatments released both types of dormancy. The removal of seed coat was essential for germination and for the induction of peroxidase, α‐amylase, and ribonuclease activities. Marked quantitative differences were found in cathodic isoperoxidases from intact and scarified seeds as early as 24 hours after imbibition suggesting their involvement in pregermination processes. Hormones had little effect on peroxidases. Inhibitor studies indicated that all isoperoxidases with the exception of one might be synthesized de novo. The enhancement of α‐amylase and ribonuclease by gibberellic acid and kinetin in scarified seeds occurred only after 24 hours. This result suggests, that gibberellin or cytokinin modulation of these enzymes might be post‐germination events and that seeds are presumably deficient in these hormones. Qualitative and quantitative changes were not detected in isoribonucleases of intact seeds. The differences in isoribonucleases between hormone treated and untreated scarified seeds appeared only after 24 hours. The enhancement of RNA polymerase activity by chilling in intact seeds at zero time and in scarified seeds at 24 hours may be due to gene derepression directly related to the release of embryonal dormancy.