Supporting Table 1 ROS detoxification

Antioxidant / Typical reaction / General references / Examples for seed studies / Seed-related references
Enzymatic
Superoxide dismutase (SOD) / 2O2˙¯ + 2H+ → H2O2 + 3O2 / Halliwell, 2006 / No change during germination in sunflower
High constitutive expression during embryogenesis in horse chestnut seeds
MnSOD expression increases during early embryo development in Arabidopsis / Bailly et al., 2004
Bagnoli et al., 1998
Otegui et al., 2002
Ascorbate peroxidase (APX) / H2O2 + 2As → DHA + 2H2O / Mittler et al., 2004 / Gibberellins repress transcription of APX in barley aleurone layer, facilitating ROS accumulation / Fath et al., 2002
Glutathione peroxidase (GPX) / H2O2 + 2GSH → GSSG + 2H2O / Mittler et al., 2004 / During drying, GPX activity is much higher in an orthodox Acer species than in a recalcitrant Acer species / Pukacka & Ratajczak, 2007a
1Peroxidase (POX) / H2O2 scavenging:
2RH + H2O2 → 2R˙ + 2H2O
ROS production
H2O2 production:
CoIII + RH2 → Fe(III) + R− + H2O2
O2˙¯ production:
CoIII → Fe(III) + O2˙¯
˙OH production:
O2˙¯ + Fe(III) → O2 + Fe(II)
2O2˙¯ + 2H+ → H2O2 + 3O2
Fe(II) + H2O2 → Fe(III) + ˙OH + OH¯ / Almagro et al., 2008
Almagro et al., 2008 / Upregulation during imbibition of cress and tomato seeds
Increased activity during pea seed imbibition
POX-mediated O2˙¯ formation during radish seed germination / Linkies et al., 2010
Morohashi, 2002
Kranner et al., 2010a
Schopfer et al., 2001
Catalase (CAT) / 2H2O2 → 2H2O + O2 / Halliwell, 2006 / Increased activity and differential expression of isoforms during seed maturation drying / Bailly et al., 2004
Peroxiredoxin (Prx) / H2O2 + Cys-SH → 2H2O + Cys-SO2H / Pulido et al., 2009 / Controls the level of H2O2 in the nucleus of germinating wheat seeds / Pulido et al., 2009
Non-enzymatic
Flavonoids / Detoxify many radicals unspecifically / Rice Evans et al., 1997 / Many seeds are rich in flavonoids, e.g. Arabidopsis and pea / Pourcel et al., 2007
2Carotenoids / Quench peroxyl radicals and 1O2 / Iannone et al., 1998 / Decline during storage in wheat seeds
Decline during storage in Araucaria seeds / Calucci et al., 2004
Hidalgo & Brandolini, 2008
Francini et al., 2006
Tocopherols / Quench lipid peroxyl radicals / Falk & Munné-Bosch, 2010 / Control of lipid peroxidation during seed germination and early seedling growth
Decline in α-tocopherol during storage of Suaeda maritima seeds / Sattler et al., 2004
Seal et al., 2010
3Glutathione (GSH) / R˙ + 2GSH → GSSG + R
GSSG + 2PSH → 2GSH + PSSG / Kranner & Birtić, 2005
Kranner et al., 2008
Colville & Kranner, 2010 / GSH conversion to GSSG during seed maturation and rapid reduction of GSSG in germinating seeds
Seed ageing induces oxidation of the remaining GSH and ability to regenerate GSH correlates with viability
GSSG accumulation correlates with embryonic axes viability loss in sweet chestnut seeds
GSH is essential for embryo development and seed maturation. Sulphur malnutrition of developing seeds results in lower GSH levels and repression of embryo development. / Tommasi et al., 2001
Kranner et al., 2006
Roach et al., 2010
Cairns et al., 2006
3Ascorbate (Asc) / H2O2 + 2As → DHA + 2H2O / De Gara et al., 2003 / Synthesis of Asc is down-regulated during seed maturation in orthodox seeds, and only trace amounts are detectable in mature seeds, because Asc stimulates cell cycle activity, which is unwanted in quiescent, orthodox seeds
Asc synthesis commences with germination
Breakdown of Asc in recalcitrant seeds correlates with desiccation-induced viability loss / Tommasi et al., 2001
Pukacka & Ratajczak, 2007a

1Peroxidases can break down H2O2 and also produce H2O2, O2˙¯ and ˙OH.

2Carotenoids are also precursors of ABA.

3ROS and antioxidants work together in the GSH-Asc cycle (Foyer & Noctor, 2005).

References

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Bailly C, Leymarie J, Lehner A, Rousseau S, Come D, Corbineau F. 2004. Catalase activity and expression in developing sunflower seeds as related to drying. Journal of Experimental Botany 55: 475-483.

Cairns NG, Pasternak M, Wachter A, Cobbett CS, Meyer AJ. 2006. Maturation of Arabidopsis seeds is dependent on glutathione biosynthesis within the embryo. Plant Physiology 141: 446-455.

Calucci L, Capochhi A, Galleschi L, Ghiringhelli S, Pinzino C, Saviozzi F, Zandomenghi M. 2004. Antioxidants, free radicals, storage proteins, puroindolines and proteolytic activities in bread wheat (Triticum aestivum) seeds during accelerated aging. Journal of Agriculture and Food Chemistry 52: 4274−4281.

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Otegui MS, Capp R, Staehelin LA. 2002. Developing seeds of Arabidopsis store different minerals in two types of vacuoles and in the endoplasmic reticulum. Plant Cell 14: 1311–1327.

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