The nuclear origin of the non‐phosphorylating NADH dehydrogenases of plant mitochondria

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Abstract
The oxidation of matrix and cytosolic NADH by isolated beetroot and wheat leaf mitochondria was investigated to determine whether the rotenone‐insensitive NADH dehydrogenases of plant mitochondria were the products of nuclear or mitochondrial genes. After aging beetroot tissue (slicing and incubating in a CaSO4 solution), the induction of the level of matrix NADH oxidation in the presence of rotenone was greatly reduced in mitochondria isolated from tissue treated with cycloheximide, a nuclear protein synthesis inhibitor. This was also true for the oxidation of cytosolic NADH. Mitochondria isolated from chloramphenicol‐treated tissue exhibited greatly increased levels of both matrix and external rotenone‐insensitive NADH oxidation when compared to the increase due to the aging process alone. This increase was not accompanied by an increase in matrix NAD‐linked substrate dehydrogenases such as malic enzyme nor intra‐mitochondrial NAD levels. Possible explanations for this increase in rotenone‐insensitive NADH oxidation are discussed. Based on these results we have concluded that the matrix facing rotenone‐insensitive NADH dehydrogenase of plant mitochondria is encoded by a nuclear gene and synthesis of the protein occurs in the cytosol.