Review on positive role of Reactive Oxygen Species (ROS) in seed germination

In many seeds, the process of germination features testa rupture and endosperm rupture are two separate events. Endosperm rupture requires cell wall weakening in the endosperm layer. Puncture force measurements are a useful tool for quantifying this endosperm weakening. Various mechanisms have been proposed to promote endosperm weakening. Endosperm weakening requires cell wall weakening. This process involves cleavage of cell wall polymers or loosening of bonds between the polymers. Several molecular mechanisms have been proposed for endosperm weakening. Most prominent among them is, cleavage of cell wall polymers in the endosperm by reactive oxygen species, or more specifically, by apoplastic hydroxyl radicals (•OH) formed when superoxide (O2−•) and hydrogen peroxide (H2O2) undergo a Fenton reaction in the presence of peroxidases. Regulation of seed germination is quite complex and is further complicated by interaction of hormones like Gibberellin (GA), Abscisic Acid (ABA) and ethylene. Moreover, the involvement of reactive oxygen species (ROS) in hormone signaling for such regulation is still less understood. Positive interactive role of ROS with GA, ABA and ethylene was observed in seed germination of Vignaradiata. ROS production is essential for lignification and cross-linking of cell wall polymers in vascular tissue. Oxidation of the germination inhibitor(s) present in the pericarp by H2O2 promotes seed germination. Antioxidants which are derivatives of well-known germination inhibitors suppressed seed germination in a dose-dependent manner. To initiate seed germination, the germination inhibitor(s) should be decomposed by an oxidant such as H2O2 .