Free radical accumulation and lipid peroxidation in testas of rapidly aged soybean seeds: a light-promoted process

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Abstract
The role of free radical-induced damage as a cause of loss of vigour in seeds is by no means resolved. In this contribution, the effects of environmental treatments known to reduce viability rapidly were compared with the effects of long-term, low-temperature storage on germination, hypocotyl growth and free radical accumulation and lipid peroxidation in soybean seeds. Accelerated aging was achieved by incubating seeds at 35°C and 1% relative humidity over H2SO4 for up to 69 days in the light and in darkness. In contrast, seeds under long-term storage were maintained at 5°C and 6% moisture content in darkness for up to 6 years. At 35°C there were rapid and significant reductions in rates of seed germination and hypocotyl extension. Loss of viability and declining vigour were associated with increases in lipid peroxidation and free radical build-up but the latter, surprisingly, was largely confined to the testa rather than the cotyledon. Exposure to light greatly enhanced lipid peroxidation and increased organic free radical accumulation in the translucent testas of seeds, but not in the cotyledons. Similar responses to light were recorded in testas detached from seeds. These results show that in soybean the testa is a significant locus of free radical degenerative events induced by high temperature combined with low moisture.