Mitochondrial Modifications Associated with the Cytoplasmic Male Sterility in Faba Beans

Abstract

Isolated mitochondria of faba beans carrying 2 different determinisms of the cytoplasmic male sterility (cytoplasms 447 and 350) were compared to fertile lines. In addition to the major mitochondrial DNA, 5 small DNA species (in the range of 1000-2000 base pairs) were detected by agarose gel electrophoresis in the 4 cytoplasms. An additional small DNA species was found specifically in the cytoplasm 350. After endonuclease restriction of the mitochondrial DNA, the patterns obtained for both male-sterile cytoplasms were identical to each other but distinct by 2-4 fragments from the patterns obtained for male-fertile cytoplasms. [35S]methionine labeling in situ of the mitochondrial protein synthesis revealed an additional polypeptide (MW = 25,000) detected only in the 2 male-sterile cytoplasms. The male-sterile cytoplasm 350 showed a decrease of the respiratory state 3 of O2 uptake during oxidation of NADH or malate + pyruvate. This decrease is thought to reflect a smaller capacity of the respiratory chain. These specific mitochondrial modifications support the hypothesis of a mitochondrial localization of the cytoplasmic male sterility determinant in faba beans.