Nonstructural carbohydrates in dormant and afterripened wild oat caryopses

Abstract

Nonstructural carbohydrates were determined in both embryo and endosperm of dormant (nongerminating) and afterripened (germinating) intact caryopses of wild oat ( Avena fatua L.). No changes in endosperm starch or soluble sugar were observed at the onset of germination (18 h). No changes in glucose, fructose, sucrose or starch within dormant or afterripened embryos correlated with onset of visual germination. In afterripened embryos, depletion of raffinose (18 h), stachyose (18 h) and galactose (24 h) was correlated with germination. In contrast, raffinose‐family oligosaccharide levels in dormant embryos remained constant for 7 days following imbibition. Germination of isolated dormant embryos on 88 m M galactose‐containing media was accompanied by decreased endogenous levels of raffinose and stachyose. Isolated embryos from dormant caryopses incorporated 14 C from 14 C‐fructose into both raffinose and stachyose during 24 h of imbibition. In contrast, no 14 C incorporation into stachyose was observed in embryos from afterripened caryopses. No 14 C incorporation into raffinose was observed at 18 and 24 h. When in vitro activities of α galactosidase were measured, no temporal differences between dormant or afterripened caryopses were detected in either embryo or endosperm tissue. Although the mechanism associated with differences in utilization of raffinose and stachyose is yet unidentified, alterations in raffinose‐family oligosaccharide metabolism in the embryo appear to be a unique prerequisite for afterripening‐induced germination.