Plant Respiration
Authors: O'Leary Brendan M , Plaxton William C 
Published: April 2016

Plant respiration is the controlled oxidation of energy‐rich photosynthetic end‐products (i.e. starch and sucrose) via the pathways of glycolysis, the tricarboxylic acid (TCA) cycle and mitochondrial electron transport chain, producing CO
2
and adenosine triphosphate (ATP). Respiration also generates low‐molecular‐weight ‘building block’ molecules needed as precursors for biosynthesis and nitrogen assimilation. Although most respiratory enzymes are common to all organisms, there are many features unique to plant respiration including the occurrence of parallel glycolytic pathways in the cytosol and plastid, and alternative ‘bypass’ enzymes in cytosolic glycolysis, and the mitochondrial TCA cycle and electron transport chain. These bypasses include glycolytic enzymes that use pyrophosphate instead of ATP and non‐energy‐conserving routes of mitochondrial electron transport. The resulting flexible nature of plant respiratory metabolism represents an essential adaptation that helps sessile plants acclimatise to the many stresses that they are exposed to in their natural environment. Genetic engineering of respiratory metabolism in transgenic plants is providing an important biotechnological approach for improving crop yields and enhancing sustainable agriculture.

Key Concepts

Respiration is represented by the combined reactions of glycolysis, the TCA cycle and the miETC.

Plant respiration produces ATP as well as biosynthetic precursors needed for growth and various metabolites needed for stress acclimation.

Comparing the organisation and control of metabolism between different organisms provides key insights into the two main themes of biology: namely, evolution and adaptation.

Carbohydrates are the dominant respiratory substrate in plants, whereas fatty acids are rarely respired.

Plant cytosolic glycolysis is a complex network containing alternative enzymatic reactions that circumvent a classical reaction dependent on ATP, ADP or phosphate as a cosubstrate.

Alternative PPi‐dependent cytosolic enzymes confer a considerable bioenergetic benefit that extends the survival time of ATP‐depleted plant cells during abiotic stresses such as anoxia or severe phosphate starvation.

PEPC is a tightly regulated enzyme situated at a crucial branch point of plant metabolism that controls anaplerotic replenishment of TCA cycle intermediates withdrawn for biosynthesis and N‐assimilation.

The operation of the TCA ‘cycle’ is flexible and changes flux modes to suit the needs of the cell.

Plants dynamically alter the efficiency of mitochondrial ATP production by their miETC via use of alternate dehydrogenases and oxidases, and UCP, thereby providing additional metabolic flexibility in an ever‐changing and stressful environment.

At the ecosystem level, plant respiration has a profound impact on the CO
2
concentration in the atmosphere, and is therefore a key component influencing the global carbon cycle and climate change.

Metabolic engineering of plant respiration is providing an important approach to enhancing crop yields, as well as a potential mechanism for mitigating global climate change owing to elevated atmospheric CO
2
levels.