High efficiency of oxidative phosphorylation in mitochondria of wheat

Mitochondria of young seedlings of a wheat hybrid 31MS × 28 exhibited high efficiency of oxidative phosphorylation. The ADP:O ratios estimated polarographically approached or were equivalent to 6, 4, and 5 with α-ketoglutarate, succinate, and malate, respectively. The respiratory control values with these substrates were about 7.5, 4.5, and 2.9. When assayed manometricafly, the P:O ratios with α-ketoglutarate as substrate and 10 min of reaction time were between 5.4 and 5.8. ADP was utilized almost exclusively in oxidative phosphorylation; microbial contamination in phosphorylating reaction mixtures had no measurable effect on oxidative phosphorylation. A concentration of 1.7 × 10−5 M 2,4-dinitrophenol had no appreciable effect on stimulation of respiration by ADP. ATPase activity was increased about 13% by dinitrophenol. It appears that high efficiency of oxidative phosphorylation is a true characteristic of the mitochondria used in this study.