Accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), that is believed not to be involved in catalysis. Complex I functions in the transfer of electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone (By similarity). Complex I is composed of at least 49 different subunits. This is a component of the iron-sulfur (IP) fragment of the enzyme. By cold. Leaves have a reduced capacity for cold acclimation, appear water-soaked, leak electrolytes, and accumulate reactive oxygen species constitutively. Sugar-sensitive germination, delayed growth, modified respiration pathway, and altered stress responses. Belongs to the complex I NDUFS4 subunit family.