LACK OF MITOCHONDRIAL AND NUCLEAR-ENCODED SUBUNITS OF COMPLEX-I AND ALTERATION OF THE RESPIRATORY-CHAIN IN NICOTIANA-SYLVESTRIS MITOCHONDRIAL DELETION MUTANTS

We previously have shown that Nicotiana sylvestris cytoplasmic male st erile (CR IS) mutants I and II present large mtDNA deletions and that the NAD7 subunit of complex I (the main dehydrogenase of the mitochond rial respiratory chain) is absent in CMS I. Here, we show that, despit e a large difference in size in the mtDNA deletion, Ch IS I and II dis play similar alterations, Both have an impaired development from germi nation to flowering, with partial male sterility that becomes complete under low light. Besides NAD7, two other complex I subunits are missi ng (NAD9 and the nucleus-encoded, 38-kDa subunit), identified on two-d imensional patterns of mitochondrial proteins, Mitochondria isolated f rom CMS leaves showed altered respiration, Although their succinate ox idation through complex II was close to that of the wild type, oxidati on of glycine, a priority substrate of plant mitochondria, was signifi cantly reduced, The remaining activity was much less sensitive to rote none, indicating the breakdown of Complex I activity, Oxidation of exo genous NADH (coupled to proton gradient generation and partly sensitiv e to rotenone) was strongly increased. These results suggest respirato ry compensation mechanisms involving additional NADH dehydrogenases to complex I, Finally, the capacity of the cyanide-resistant alternative oxidase pathway was enhanced in CMS. and higher amounts of enzyme wer e evidenced by immunodetection.