Metabolism-induced free radical activity does not contribute significantlyto loss of viability in moist-stored recalcitrant seeds of contrasting species

Because recalcitrant seeds are not desiccation-tolerant they must be stored moist. Their limited storage potential presents significant practical prob lems, but the cause of viability loss is not known. It has been suggested t hat a stress-induced metabolic imbalance can develop during storage that re sults in free-radical generation and consequent damage. To investigate this hypothesis, the presence of a stable free radical, lipid peroxidation and representative enzymatic and nonenzymatic protection mechanisms against oxi dative attack were monitored in nondormant recalcitrant seeds during moist storage. A comparison was made between seeds of a short-lived subtropical s pecies (Avicennia marina) and two longer-lived temperate species (Quercus r obur and Castanea sativa). As a test of the hypothesis, seeds of both tempe rate species were held under conditions of elevated temperature and oxygen concentration to develop different rates of respiration during storage. The number of normal seedlings produced from seeds of the two temperate specie s declined during storage, but viability remained high, so effects of agein g were not confounded with an increasing proportion of dead seeds in the po pulation. Under these conditions, lipid peroxidation changed little over th e storage period, although there was evidence of accumulation of a stable f ree radical in Q. robur axes. However, this response was not affected by st orage conditions that elevated respiration rates. In the shorter-lived A. m arina seeds viability declined soon after the start of storage, but the sig nificant increase in free radicals shown by EPR measurement was only eviden t when an increasing percentage of the seed population was no longer viable . Changes in the activity of scavenging enzymes and the concentration of an tioxidants were time-dependent and not related to respiration rates. Theref ore, in the present work, no consistent evidence was found to show that met abolism-induced free-radical activity was a significant contributing factor to pre-mortem deterioration in moist-stored recalcitrant seeds.