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Studies on the Respiratory Properties of Mitochondria Isolated from Developing Winter Wheat Seedlings ¹

^a Chemistry and Biology Research Institute, Agriculture Canada, Ottawa, Ontario K1A OC6, Canada

Mitochondria isolated from shoots of 2 days, light- and dark-grown winter wheat (Triticum aestivum L. cv. Rideau) seedlings oxidize -ketoglutarate and L-malate with good respiratory control and ADP: O ratios. The efficiency of oxidative phosphorylation, and respiratory control are both reduced significantly when succinate or NADH is employed as substrate. Respiratory control values and ADP: O ratios show a general decline in mitochondria from seedlings of increasing age, whether grown in light or dark. In light-grown seedlings, the decrease in respiratory control with aging is due principally to a decrease in the rate of state 3 respiration, while in dark-grown material, the decrease appears to be due mainly to an increased rate of state 4 respiration. In both light- and dark-grown seedlings, oxygen consumption during state 3 respiration is severely inhibited by oligomycin. During state 4 respiration, 2,4-dinitrophenol stimulates oxygen uptake to a level approximately two-thirds the normal ADP-stimulated rate.