Respiratory Properties of Developing Bean and Pea Leaves

Abstract

The rate of O₂ uptake in the dark in bean leaves and leaf slices decreased during development. The use of inhibitors of the cytochrome and alternative pathways and the uncoupier carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) indicated that this decline was largely due to a decline in the activity and capacity of the cytochrome path. However, the capacity of the alternative path remained more or less constant with leaf expansion, and thus percentage cyanide resistance of respiration increased with leaf expansion. The activity of the alternative path was small in bean leaves and leaf slices, and decreased during development. Respiration, mainly the cytochrome pathway, of bean leaf slices was stimulated by FCCP at all ages, the stimulation being more pronounced in young leaves. The rate of overall respiration, the activities of the cytochrome and alternative paths, and the extent to which FCCP stimulated respiration in bean leaf slices were positively correlated with endogenous free sugar levels during aging. Similar trends were observed with mitochondria isolated from pea leaves. Leaf mitochondria from older plants had lower cytochrome path capacity, but the capacity of the alternative path remained much the same as that in leaf mitochondria from seedlings.