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

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 Fredrick wheat. Partial ice encasement and exposure to a nitrogen atmosphere at -1 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.