FIGURE 1.

Illustration of H₂O₂ functions during seed germination. Water uptake by seeds is fundamental for the reactivation of metabolism processes, for breaking dormancy and for seed germination. During imbibition, H₂O₂ production occurs through respiratory activities of mitochondria, through activities of β-oxidation pathways and through enzymes such as NADPH oxidases, extracellular peroxidases, and oxalate oxidases. H₂O₂ levels are also precisely controlled via antioxidative mechanisms. Signaling functions of H₂O₂ and crosstalk with other molecules and phytohormones and the selective oxidation of proteins and mRNA play key roles in germination regulation. H₂O₂ directly interrupts dormancy, weakens endosperm, induces PCD in aleurone cells and can present antimicrobial properties.