FREE-RADICAL ACCUMULATION AND LIPID-PEROXIDATION IN TESTAS OF RAPIDLYAGED SOYBEAN SEEDS - A LIGHT-PROMOTED PROCESS

The role of free radical-induced damage as a cause of loss of vigour i n seeds is by no means resolved. In this contribution, the effects of environmental treatments known to reduce viability rapidly were compar ed with the effects of long-term, low-temperature storage on germinati on, hypocotyl growth and free radical accumulation and lipid peroxidat ion in soybean seeds. Accelerated aging was achieved by incubating see ds at 35 degrees C and 1% relative humidity over H2SO4 for up to 69 da ys in the light and in darkness. In contrast, seeds under long-term st orage were maintained at 5 degrees C and 6% moisture content in darkne ss for up to 6 years. At 35 degrees 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 l ipid peroxidation and free radical build-up but the latter, surprising ly, was largely confined to the testa rather than the cotyledon. Expos ure 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 hig h temperature combined with low moisture.