Increased participation of pentose phosphate pathway in response to afterripening and gibberellic acid treatment in caryopses of Avena fatua

The rates of oxygen consumption of dormant and non-dormant excised embryos of Avena fatua L. before germination are similar. Gibberellic acid (GA) treatment stimulates germination of dormant embryos without affecting oxygen consumption. Thus dormancy is not the result of restricted oxygen uptake. The fat content of dormant and non-dormant caryopses remains constant during germination. Dormant and non-dormant embryos have respiratory quotients near unity supporting the hypothesis that starch degradation occurs before germination. 6-Phosphogluconate dehydrogenase, a key enzyme of the pentose phosphate pathway, is present in dormant and non-dormant dry embryos but the pre-germination C6/C1 ratio of non-dormant embryos is markedly lower than that of dormant embryos, indicating a greater participation of the pentose phosphate pathway in the respiratory metabolism of non-dormant embryos. Release from dormancy is associated with a shift in metabolism from the glycolytic pathway to the pentose phosphate pathway. GA treatment, which stimulates germination of dormant embryos, causes a similar qualitative change in the oxidative metabolism of dormant embryos. Thus the action of GA is to cause the increased degradation of glucose via the pentose phosphate pathway, which is an essential step in the preparation for germination.