Alternative Respiratory Pathway

Abstract

O2 uptake during the 1st hours of imbibition in intact Ransom soybeans (Glycine max [L.] Merr.) and mung beans (Phaseolus aureus Roxb.) seeds showed a marked sensitivity to potassium cyanide but was unaffected by addition of either salicylhydroxamic acid or propyl gallate. However, O2 uptake by finely ground seed particles was very sensitive to the addition of either compound. O2 uptake in intact, imbibing seeds was associated with a cyanide-sensitive process, most probably mitochondrial mediated respiration, and not the result of the cyanide-insensitive lipoxygenase activity which was readily detectable in ground seed particles. The antioxidant propyl gallate inhibited specifically alternative pathway electron transfer in isolated mung bean mitochondria. Half-maximal inhibition occurred with 2-5 .mu.M propyl gallate. Kinetic analysis indicated that propyl gallate inhibition of the alternative pathway occurred at, or very near, the site of inhibition of the alternative pathway by salicylhydroxamic acid. A high level of lipoxygenase activity was associated with washed mitochondria isolated from a variety of etiolated plant tissues. Most of this lipoxygenase activity could be eliminated from mung bean mitochondria if the mitochondria were purified on a discontinuous sucrose gradient. The mitochondrial-associated activity was probably the result of nonspecific adsorption of lipoxygenase onto the mitochondrial membranes during isolation.