Association of lipid oxidation with seed ageing and death

Abstract

SEEDS usually exhibit their maximum germination potential soon after harvest, and as storage time increases, they lose vigour and eventually die. The rate of physiological ageing generally increases with increased moisture content and temperature¹. In addition, certain xerophytic storage fungi (primarily Aspergillus spp.) can attack seeds in storage when seed moisture content is in equilibrium with relative humidities greater than 65% (ref. 1), and cause changes that mimic physiological ageing. Physiological changes accompanying physiological ageing^1–5 and attack by storage fungi⁵ have been catalogued, but the basic biochemical events leading to these changes are not known. Harrington¹ and Pammenter et al.⁶, however, have suggested that oxidation of unsaturated lipids may lead to free-radical formation. Free radicals may then damage cellular membranes and react destructively with macromolecules. Similar suggestions have been presented to explain ageing in several other systems⁷, and the results of experiments reported here indicate that free-radical formation may be important in seed deterioration. Theories of mechanisms of lipid oxidation indicate that fatty acids with two or more unsaturated bonds should be more labile and prone to form free radicals than more highly saturated acids^8,9. Thus, if fatty acid oxidation and free-radical formation are occurring, the highly unsaturated acids should decrease as seeds deteriorate, whereas the quantity of saturated fats should remain constant in the absence of beta oxidation.