Species‐Specific Enzymatic Tolerance of Sulfide Toxicity in Plant Roots and Comparative Susceptibility between Plant and Catfish Tissue

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Sulfide is a potent inhibitor of numerous enzymes, especially cytochrome c oxidase, which catalyzes the terminal step in aerobic respiration. However, some salt marsh plants live in sulfide-rich sediments. We hypothesized salt marsh plants might tolerate sulfide exposure better compared to upland plants at the metabolic level. Two enzymes were assayed to determine broader effects of sulfide toxicity on metabolism. Our objective was to compare roots of various plant species and catfish liver and muscle tissues. Cytochrome c oxidase and alcohol dehydrogenase activities were measured in root extracts and tissue homogenate exposed to 0, 5, 10, 15, and 20 μM sodium sulfide. Activities of cytochrome c oxidase were very sensitive to sulfide and were nearly undetectable at 5 to 10 μM sulfide. Alcohol dehydrogenase activities were less sensitive to sulfide, typically only reduced by about 50% at 20 μM sulfide. Cytochrome c oxidase activities in root extracts of flooding-sensitive plant species decreased to nearly zero when treated with 5 μM sulfide, whereas activities in some salt marsh plants did not decrease until 10 μM sulfide. Cytochrome c oxidase activities in catfish tissues were much higher than those measured in plant roots, but were very sensitive to increasing sulfide concentrations, with complete inhibition at 5 μM sulfide. Cytochrome c oxidase activities in some salt marsh plants were low even in the absence of sulfide, perhaps an adaptation to avoid sulfide vulnerability in their native habitat. This illustrates potent metabolic effects of sulfide, and variability in sulfide toxicity among plants. This work was supported by the Kansas Academy of Science and Kansas IDeA Network of Biomedical Research Excellence.