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Oxidative Stress and Death Phenomena

Damage to macromolecules by oxidative stress causes loss of seed viability (Annex 1)

This project is one of a series in the theme 'Science of Seed Ageing'.

The 'free-radical theory of ageing', proposed by Denham Harman in the mid-1950s, predicts that the continuous formation of reactive oxygen species (ROS) throughout the life of an organism, leads to cumulative damage, ageing and death.  Recent evidence confirms that the production of oxidants together with the ability to scavenge ROS is intricately connected to ageing and life-span. This applies to all organisms, and the seeds of higher plants are no exception. However, their desiccation tolerance allows ‘orthodox seeds’ to survive at very low intracellular water contents and with almost no metabolic activity, and therefore to live longer than most other organisms. However, even when stored at optimal conditions in seed banks, seeds are not immortal. Evidence is accumulating that some species die faster than previously expected and some species have intrinsically short life-spans. The highly reactive ROS, some of them having a half-life of only a few nanoseconds, are amongst the most likely to cause damage.

In this project, free radical-induced damage (Annex 1) as a cause of seed death is being studied: 1) Free radical attack during ageing is counteracted by antioxidants in viable seeds. Following previous work on the breakdown of antioxidants in other organisms , we have shown that the breakdown of antioxidants correlates with seed viability loss. 2) The failure of the antioxidant system gives rise to lipid peroxidation, and volatile hydrocarbons and lipid peroxides are formed. One project aim is to relate the volatile fingerprint of seeds to the mechanisms of viability loss during seed ageing. 3) Breakdown of lipids and membrane proteins consequently cause membrane damage. Studying changes in fatty acid composition and measuring membrane leakage allow for an assessment of seed viability, studied e.g., in Vitellaria paradoxa. Overall, we endeavour to achieve a synthesis of the biochemical pathways of ROS-provoked seed death. See Annex 2 for publications of relevance to or emanating from this project.

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