Measurement of Mitochondrial Respiration in Isolated Protoplasts: Cytochrome and Alternative Pathways

Plant mitochondria are characterized by the presence of both phosphorylating (cytochrome) and non-phosphorylating (alternative) pathways, the activity of which directly affects the efficiency of mitochondrial energy conservation. The cyanide-insensitive AOX (alternative oxidase) is located on the inner surface of the inner membrane, results in the oxidation of ubiquinol and the net reduction of oxygen to water, is non-protonmotive and is considered to be one of the newest members of the di-iron carboxylate group of proteins. In thermogenic tissues it plays a key role in pollination and the maintenance of a warm environment for the flower, whereas in non-thermogenic tissues functions include acting as an energy overflow, part of the oxygen defence mechanism and maintaining plant growth homoeostasis.

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The uncoupling of respiration in plant mitochondria: keeping reactive oxygen and nitrogen species under control

Journal of Experimental Botany ◽

10.1093/jxb/eraa510 ◽

2020 ◽

Author(s):

Vasily N Popov ◽

Mikhail Y Syromyatnikov ◽

Alisdair R Fernie ◽

Subhra Chakraborty ◽

Kapuganti Jagadis Gupta ◽

...

Keyword(s):

Mitochondrial Respiration ◽

Uncoupling Protein ◽

Plant Mitochondria ◽

Reactive Oxygen ◽

Stress Factors ◽

Atp Production ◽

Alternative Pathways ◽

Mitochondrial Functions ◽

Far From Equilibrium

Abstract Plant mitochondrial respiration involves the operation of various alternative pathways. These pathways participate, both directly and indirectly, in the maintenance of mitochondrial functions though they do not contribute to energy production, being uncoupled from the generation of an electrochemical gradient across the mitochondrial membrane and thus from ATP production. Recent findings suggest that uncoupled respiration is involved in reactive oxygen species (ROS) and nitric oxide (NO) scavenging, regulation, and homeostasis. Here we discuss specific roles and possible functions of uncoupled mitochondrial respiration in ROS and NO metabolism. The mechanisms of expression and regulation of the NDA-, NDB- and NDC-type non-coupled NADH and NADPH dehydrogenases, the alternative oxidase (AOX), and the uncoupling protein (UCP) are examined in relation to their involvement in the establishment of the stable far-from-equilibrium state of plant metabolism. The role of uncoupled respiration in controlling the levels of ROS and NO as well as inducing signaling events is considered. Secondary functions of uncoupled respiration include its role in protection from stress factors and roles in biosynthesis and catabolism. It is concluded that uncoupled mitochondrial respiration plays an important role in providing rapid adaptation of plants to changing environmental factors via regulation of ROS and NO.

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