A Role for Reactive Oxygen Species in Endosperm Weakening

摘要

In many seeds, including the established model species Arabidopsis (Arabidopsis thaliana (L.) Heynh.) and the emerging Brassicaceae model system garden cress (Lepidium sativum L.), the process of germination features testa rupture and endosperm rupture as 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. We have established such measurements for L. sativum and have shown that endosperm weakening takes place prior to endosperm rupture. Various mechanisms have been proposed to promote endosperm weakening. A novel mechanism proposed by us involves the cleavage of cell wall polymers in the endosperm by reactive oxygen species, or more specifically, by apoplastic hydroxyl radicals (OH) formed when superoxide (O_2~-) and hydrogen peroxide (H_2O_2) undergo a Fenton reaction in the presence of peroxidases.