THE EXPRESSION OF DESICCATION-INDUCED DAMAGE IN ORTHODOX SEEDS IS A FUNCTION OF OXYGEN AND TEMPERATURE

From the premise that desiccation-induced damage is associated with a free-radical mechanism of injury, we address the hypothesis that expre ssion of desiccation damage is dependent on metabolism. The effects of temperature and O-2 concentration on the expression of damage were st udied in germinating bean (Phaseolus vulgaris L. cv. Pole Kentucky Won der) axes and maize (Zea mays L. cv. Kelvedon Glory) radicles submitte d to flash drying. Damage in desiccation-tolerant and -intolerant mate rial was assessed by measurements of electrolyte leakage and accumulat ion of a stable free radical. In desiccation-tolerant material leakage rates remained low during water removal. In contrast, in desiccation- intolerant tissues, leakage profiles revealed the presence of a critic al moisture content below which leakage rates increased sharply. In th e desiccation-intolerant stage, a highly significant correlation was f ound between critical moisture contents and temperatures of drying. Th e concentration of the stable radical was lower if tissues were dried below 15 degrees C and higher when tissues were dried at 30 degrees C and above. Both leakage and build up of free radicals were highly sens itive to O-2 concentrations: damage was lower when tissues were dried in the presence of N-2, but increased several-fold when tissues were e xposed to O-2 concentrations between 2 and 100%. In contrast, neither temperature nor O-2 concentrations affected electrolyte leakage in des iccation-tolerant samples. Treatment with a respiration inhibitor (KCN ) prior to drying reduced the desiccation sensitivity of tissues, as n oted by a reduction of the critical moisture content. We conclude that the expression of desiccation damage depends on the drying history an d that factors that limit metabolism also reduce the incidence of desi ccation injury.