title: Dark-mediated dormancy release in stratified Lolium rigidum seeds is associated with higher activities of cell wall-modifying enzymes and an apparent increase in gibberellin sensitivity.
abstract: Dormancy release in freshly matured, imbibed annual ryegrass (Lolium rigidum) seeds is inhibited by light and involves a decrease in seed sensitivity to abscisic acid. Other processes involved in dormancy release in the dark were investigated by measuring seed storage compound mobilisation and the activity of cell wall-degrading enzymes. Activities of endo-β-mannanase and total peroxidase were higher in dark-stratified compared to light-stratified seeds, indicating that weakening of the structures constraining the embryo was accelerated in the dark. A dramatic degradation of storage proteins in light-stratified seeds, accompanied by induction of a high molecular mass protease, suggests that maintenance of storage(-like) proteins is also important in dark-mediated dormancy release. α-Amylase activity was induced in dark-stratified seeds at least 48 h prior to radicle emergence upon transfer to conditions permitting germination, or in light-stratified seeds supplied with exogenous gibberellin A(4). This suggests that (a) α-amylase is involved in stimulation of germination of non-dormant L. rigidum seeds, and (b) dark-stratified seeds have an increased sensitivity to gibberellins which permits the rapid induction of α-amylase activity upon exposure to germination conditions. Overall, it appears that a number of processes, although possibly minor in themselves, occur in concert during dark-stratification to contribute to dormancy release.
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology (M086), University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia. danica@plants.uwa.edu.au
authors.forename: Danica E
authors.initials: DE
authors.lastname: Goggin
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Powles
authors.forename: Peter E
authors.initials: PE
authors.lastname: Toorop
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Steadman
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D002473:Cell Wall / Q000378:metabolism*; D003624:Darkness; D018525:Germination / Q000528:radiation effects; D005875:Gibberellins / Q000378:metabolism*; D050356:Lipid Metabolism; D008129:Lolium / Q000166:cytology / Q000201:enzymology / Q000502:physiology* / Q000528:radiation effects; D009195:Peroxidase / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism*; D055314:Seed Storage Proteins / Q000378:metabolism*; D012639:Seeds / Q000502:physiology / Q000528:radiation effects; D000516:alpha-Amylases / Q000378:metabolism; D044902:beta-Mannosidase / Q000378:metabolism
chemical_list: D005875:Gibberellins; D010937:Plant Growth Regulators; D055314:Seed Storage Proteins; D000040:Abscisic Acid; D009195:Peroxidase; D000516:alpha-Amylases; D044902:beta-Mannosidase