Cyanide-insensitive Respiration in Plant Mitochondria

Area of Science:

• Plant physiology
• Mitochondrial respiration
• Biochemistry

Background:

• Cyanide-resistant respiration is observed in plant mitochondria.
• This pathway bypasses the traditional cytochrome c oxidase.
• The alternative oxidase's properties remain incompletely understood.

Purpose of the Study:

• To investigate the characteristics of the cyanide-resistant respiratory pathway in plants.
• To identify the components and mechanisms of the alternative oxidase.
• To compare plant and animal mitochondrial electron transport.

Main Methods:

• Isolation of mitochondria from mung bean seedlings and skunk cabbage.
• Measurement of respiratory activity and enzyme kinetics.
• Spectroscopic analysis of cytochromes.
• Inhibition studies using specific chemical agents.

Main Results:

• A significant flux through an alternative oxidase with high oxygen affinity was observed.
• This alternative oxidase is distinct from cytochromes a and a(3).
• Cytochromes b are not essential for the cyanide-resistant pathway.
• Inhibitors like thiocyanate and alpha,alpha'-dipyridyl selectively target the alternative pathway.

Conclusions:

• Plant mitochondria utilize a cyanide-resistant alternative oxidase pathway.
• This pathway likely involves a non-heme iron protein.
• The respiratory chain bifurcates prior to the antimycin-sensitive site.