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Chapter 14

Respiration and
Photorespiration

CHAPTER OUTLINE
Introduction
14.1 Overview of respiration
14.2 Citric acid cycle
14.3 Plant mitochondrial electron transport
14.4 Plant mitochondrial ATP synthesis
14.5 Regulation of mitochondrial respiration
14.6 Interactions between mitochondria and other cellular compartments
14.7 Biochemical basis of photorespiration
14.8 Photorespiratory pathway
14.9 Role of photorespiration in plants

James N. Siedow
David A. Day

 

 

Chapters 12 and 13 have described how plants use light energy to assimilate carbon into sugars and starch and how these molecules are subsequently broken down and converted into organic acids and other compounds. In this chapter we examine aerobic respiration— the further oxidation of these compounds to CO2 and H2O in the mitochondrion—and review the mechanisms by which the energy released during respiration is conserved as ATP, a process called oxidative phosphorylation. We examine how plants can minimize ATP production while maintaining respiration rates, a mitochondrial attribute that may affect plant responses to environmental stress. We also describe how mitochondria and other cellular compartments interact by means of substrate shuttles across the inner mitochondrial membrane.
      In addition to aerobic respiration, another respiratory process takes place in the leaves of many plants. This novel process, photorespiration, is the light-dependent release of CO2 and uptake of O2. The O2 uptake occurs in the chloroplast as a result of the oxygenase reaction of Rubisco, which leads to production of phosphoglycolate. Metabolism of this compound involves a complex interaction among chloroplasts, peroxisomes, and mitochondria and leads to release of CO2. Although photorespiration in effect drains carbon from plants and adversely affects growth, the process seems to be an unavoidable side reaction of CO2 fixation in most plants. Some plants, however, have evolved special anatomical and biochemical features that minimize the oxygenase reaction. These plants, known as C4 plants and Crassulacean acid metabolism (CAM) plants (see Chapter 12), demonstrate very low rates of photorespiration.


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