Discussion
Rotenone is a chemical often used to kill insect pests on crop plants and fishes in lakes. Rotenone acts by inhibiting electron transport from the NADH dehydrogenase enzyme in Complex I to ubiquinone in the mitochondrial electron transport chain. Which one of the following explains why plants can tolerate rotenone application?
Answer: D
Plants tolerate rotenone because they have additional NAD(P)H dehydrogenases that are resistant to rotenone.
Plant mitochondria possess alternative, type II NAD(P)H dehydrogenases on both faces of the inner membrane. They pass electrons from NADH or NADPH directly to ubiquinone without going through Complex I and without pumping protons, and they are insensitive to rotenone. When rotenone blocks Complex I, electrons still reach the rest of the chain through these bypass enzymes, so respiration continues.
Plant Complex I itself is rotenone-sensitive, and tolerance is not attributed to degradation of the compound or to specific efflux channels. Insects and fish lack the bypass, which is why rotenone kills them.
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