Respiratory activities, cytochrome composition and cytochrome c oxidase subunit II levels of mitochondria from alloplasmic wheats having aegilops cytoplasms

Respiratory activities, cytochrome composition and cytochrome c oxidase (EC 1.9.3.1) subunit II (COXII) levels of isolated mitochondria in one euplasmic and four alloplasmic lines of wheat (Triticum aestivum), having cytoplasms of Aegilops columnaris, Ae.crassa (4×),Ae. mutica and Ae. triuncialis, which show various growth abnormalities, were studied. Cytoplasm-specific variation on the respiratory activities has been revealed among the cytoplasms of five Triticum and Aegilops species. The cyanide-resistant respiratory pathway does not seem to contribute to the variation in activity. The low level of state 3 and cytochrome oxidase activities were evident in lines having Ae. columnaris and Ae. triuncialis cytoplasms, which also show growth inhibition. The low cytochrome oxidase activity in both cytoplasms is consistent with the low amount of cytochrome aa₃ and the severe reduction in COXII levels. The relatively low amount of cytochrome aa₃ in Ae. mutica is also consistent with the reduced level of the COXII. On the other hand, relatively low amounts of cytochrome b (b-557) are found in the Ae. crassa cytoplasmic line. These results suggest that the growth abnormalities found in the alloplasmic wheat lines are related to the variation in respiratory activities and cytochrome composition. In particular, growth inhibition found in the alloplasmic wheats having Ae. columnaris and Ae. triuncialis may be caused by the severe depression of respiratory activity due to the impaired cytochrome oxidase activity of their mitochondria.