Toxicity of Anaerobic Metabolites Accumulating in Winter Wheat Seedlings during Ice Encasement

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Abstract
Ice encasement damages cold-hardened winter wheat without major disruption of cellular organelles. CO2 accumulates during total ice encasement to higher levels in ''Kharkov'' than in less hardy ''Frederick'' wheat. Partial ice encasement and exposure to a N atmosphere at -1.degree. C allows greater CO2 accumulation but neither treatment is as damaging as total ice encasement. Lactic acid accumulates to low levels only during the 1st day of encasement and thereafter remains constant. Exposure of plants to a combination of 50% CO2 and 5% ethanol reduces survival, with a cultivar difference similar to that found in ice-encased plants. Plants in CO2 and ethanol show a proliferation of membranes and nuclear condensation similar to that in cells of ice-encased plants. Permeability increases markedly in the presence of CO2 and ethanol, to levels similar to or greater than those of iced plants. Ethanol alone does not increase permeability but in combination with CO2 raises permeability of the less hardy ''Fredrick'', although not of ''Kharkov'', but reduces survival of both cultivars. A comparison of the endogenous levels of ethanol, CO2 and lactic acid at the 50% kill point of plants due to ice encasement or due to externally supplied metabolite indicates that only CO2 accumulates to independently toxic levels. Permeability and ultrastructural evidence suggest that CO2 and ethanol in combination are the agents reducing plant viability during ice encasement.