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 injur\. we address the hypothesis thai expression of desiccation damage is dependent on metabolism. The effects of temperature and O, concentration on the expression of damage were studied in germinating bean [Phaseoius vuigaris L. cv. Pole Kentucky Wtinder) axes and maize {Zea mavs L. cv. Kelvedon G]or\> radicles submitted to flash drying. Damage in desiccation tolerant and -intolerant material was assessed by measurements of electrolyte leakage and accumulation of a stable free radical, [n desiccalion-toierant material leakage rates remained low during water removal. In contrast, in desiccation-intolerant tissues, leakage profiles revealed the presence of a critical moisture conlent below which leakage rates increased sharply. In the desiccation-intolerant stage, a highly significant con'elation was found between critical moisture contents and temperatures of drjing. The concentration ofthe stahle radical was lower if tissues were dried below ] 5'^C and higher when tissues were dried at .30°C and above. Both leakage and build up of free radicals were highly sensitive to O, concentrations: damage was lower when tissues were dried in the presence of N,. but increased several-fold when tissues were exposed to O; concentrations between 2 and lOO f̂. In contrast, neithei temperature nor O; concentrations affected electrolyte leakage in desiccation-tolerant samples. Treatment with a respiration inhibitor (KCN) prior to drying reduced the desiccjtion .sensitivitv of tis.sues. as noted by a reduction ot the critical moisture content. We conclude that the expression of desiccation damage depends on the drying history and that factors that limit metabolism also reduce the incidence of desiccation injur\.