| Abstract | Owing to its role in oxidizing reduced organic compounds to CO₂, respiration is often considered catabolic and respiratory CO₂ evolution as wasteful for plants. Therefore, there have been attempts to select plants with lower respiration to improve productivity. Genetic modification of respiratory enzymes confirms that respiration is important in growth and maintenance. For example, glycolysis is crucial for root growth. The oxidative pentose phosphate pathway is essential in supplying reduced nicotinamide adenine dinucleotide phosphate for defense mechanisms against pathogens. The tricarboxylic acid (TCA) cycle is indispensable for reproductive growth, biosynthesis of metabolites such as lipids, and productivity. The cytochrome pathway regulates stress tolerance and growth. The cyanide-resistant pathway is anabolic, providing carbon skeletons through glycolysis and the TCA cycle under conditions when the cytochrome pathway is limiting. Enhanced anaerobic respiration leads to improved flood tolerance. Transgenic Arabidopsis with partially suppressed mitochondrial pyruvate dehydrogenase kinase (mtPDHK) with subsequent increases in mtPDH activity and respiration leads to increased reproductive growth and yield especially under high CO₂, when photoassimilates are higher than at ambient CO₂. Collectively, these emerging data reaffirm the importance of respiration in biosynthetic processes, for example, oil synthesis and stress responses, and that increasing respiration somewhat may, in fact, enhance productivity. |
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