Carbohydrate concentrations and interactions in afterripening-responsive dormant Avena fatua caryopses induced to germinate by gibberellic acid

It has been proposed that gibberellic acid (GA3) promotes germination by overcoming restrictions in sugar production and utilization in afterripening-responsive dormant caryopses. While their germination rates were similar, germination commenced sooner in afterripened wild oat (Avena fatua L.) caryopses than in dormant caryopses treated with GA3 and dormant excised embryos treated with GA3 plus fructose (Fru). Limited germination occurred in dormant excised embryos cultured with GA3 alone. Carbohydrate concentrations were measured over time in dormant caryopses and excised embryos whose germination was induced with GA3 and GA3 plus Fru. The concentration of sucrose (Suc) in the endosperm declined prior to germination of dormant GA3-treated caryopses. Raffinose (Raf) family oligosaccharides in the embryos of dormant GA-treated caryopses remained relatively constant prior to and shortly after the onset of germination. In contrast, Raf family oligosaccharides in the embryos of afterripened caryopses declined prior to germination. Together this suggests Raf family oligosaccharide utilization is not associated with germination per se. Increased starch levels, which occurred in dormant excised embryos treated with Fru and GA3 plus Fru, were associated with dormancy because similar effects were not apparent in afterripened embryos cultured with Fru. An initial decline in the concentration of Raf family oligosaccharides in dormant embryos cultured with GA3 or GA3 plus Fru seems to be a result of the excision process. GA3 appears to stimulate the germination of dormant embryos by enhancing the uptake or utilization of Fru. It appears that GA3 and afterripening-induced changes in carbohydrate utilization in dormant caryopses are different.