Wheat seed ageing viewed through the cellular redox environment and changes in pH

Abstract

To elucidate biochemical mechanisms leading to seed deterioration, we studied 23 wheat genotypes after exposure to seed bank storage for 6–16 years compared to controlled deterioration (CD) at 45 °C and 14 (CD14) and 18% (CD18) moisture content (MC) for up to 32 days. Under two seed bank storage conditions, seed viability was maintained in cold storage (CS) at 0 °C and 9% seed MC, but significantly decreased in ambient storage (AS) at 20 °C and 9% MC. Under AS and CS, organic free radicals, most likely semiquinones, accumulated, detected by electron paramagnetic resonance, while the antioxidant glutathione (GSH) was partly lost and partly converted to glutathione disulphide (GSSG), detected by HPLC. Under AS the glutathione half-cell reduction potential (E_GSSG/2GSH) shifted towards more oxidising conditions, from −186 to −141 mV. In seeds exposed to CD14 or CD18, no accumulation of organic free radicals was observed, GSH and seed viability declined within 32 and 7 days, respectively, GSSG hardly changed (CD14) or decreased (CD18) and E_GSSG/2GSH shifted to −116 mV. The pH of extracts prepared from seeds subjected to CS, AS and CD14 decreased with viability, and remained high under CD18. Across all treatments, E_GSSG/2GSH correlated significantly with seed viability (r = 0.8, p<.001). Data are discussed with a view that the cytoplasm is in a glassy state in CS and AS, but during the CD treatments, underwent transition to a liquid state. We suggest that enzymes can be active during CD but not under the seed bank conditions tested. However, upon CD, enzyme-based repair processes were apparently outweighed by deteriorative reactions. We conclude that seed ageing by CD and under seed bank conditions are accompanied by different biochemical reactions.

Keywords:

• Antioxidants
• EPR
• ESR
• gene bank
• germination
• organic radicals
• seed longevity

Acknowledgements

We gratefully acknowledge support by Sibylle Pistrick, Anita Winger, Annett Marlow, Stefanie Thumm, Peter Schreiber and Michael Grau for excellent technical support and Gerald Kastberger and Anja Krieger-Liszkay for critical comments on the figures and the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the EU (FP7 grant 311840 “EcoSeed” (Impacts of Environmental Conditions on Seed Quality)) and the French Infrastructure for Integrated Structural Biology (FRISBI) ANR-10-INBS-05.