Carbohydrate status in dormant and afterripened excised wild oat embryos

Germination and carbohydrate concentrations were determined in excised dormant and afterripened wild oat (Avena fatua L. line M73) embryos cultured on N6 medium with and without 88 mM fructose (Fru). Without Fru dormant embryos began to germinate after approximately 2 weeks, and the germination rate was greater at 12 than 16°C. With addition of Fru 80% of dormant embryos germinated in 3 days. More than 80% of afterripened embryos germinated within 1 day on N6 with or without additional sugars. Therefore, relative to afterripened embryos, true embryo dormancy exists in line M73. Concentrations of starch and soluble sugars were initially similar in dormant and afterripened embryos. Culturing dormant and afterripened embryos on medium with Fru resulted in concentrations of glucose (Glu), sucrose (Sue), Fru and maltose (Mal) that were the same or higher than the initial levels. The concentration of starch in embryos initially increased slightly then remained constant or declined, except in dormant embryos on Fru-amended medium, where starch accumulated to 34 μg Glu equivalents (mg fresh weight)^-1 at 52 h. Raffinose (Raf) and stachyose (Stach) concentrations declined over time in all embryos. Carbohydrate concentrations in afterripened embryos on medium without Fru decreased to nearly undetectable levels by 52 h. Soluble sugar concentrations in dormant embryos on medium without Fru also declined by 52 h, but changes were not as extensive as those in afterripened embryos without Fru. In 52 h Raf and Stach were nearly depleted in all afterripened embryos, and in dormant embryos cultured on Fru-containing medium but not in dormant embryos without Fru. The concentration of Stach in dormant embryos without Fru declined 60% at 12 to 18 days coinciding with the potential for germination. The results demonstrate that a decline in Stach concentration is associated with the potential for germination of dormant (D) excised embryos. The mechanism of dormancy-breaking associated with the Raf family oligosaccharides remains to be determined.