Endogenous hormones in afterripening wild oat (Avena fatua) seed

Levels of gibberellins and cytokinins in dormant Avena fatua L. seeds were measured by bioassay during the afterripening process. Little change in the level of either hormone was detected in the dry seed. Following imbibition of fully afterripened seed, however, gibberellin levels increased while cytokinin levels declined. Seed strains varying in their degree of dormancy were also analysed for hormone levels; a significantly higher level of cytokinin activity was found in the most dormant strain compared with the least dormant strain. Low levels of bound hormones, including cytokinin ribotides and gibberellin glucose conjugates, were detected following enzyme hydrolysis but neither class of compounds varied greatly in level during afterripening.The major cytokinins detected in Avena fatua seeds cochromatographed with zeatin-9-glucoside, zeatin riboside, and zeatin on both HPLC columns and chromatography paper. The major gibberellin activity cochromatographed with GA4/GA7 on silica gel partition columns and thin-layer plates.Germination studies demonstrated that GA4/7 is significantly more active than GA3 in promoting the germination of dormant Avena fatua seeds. External applications of cytokinins were not found to affect the germination of dormant seed, but did promote germination in partially afterripened material.