This chapter discusses modern aerobic organisms that transduce the chemical bond energy of food molecules into the bond energy of adenosine triphosphate (ATP). It examines how aerobic organisms perform this feat where oxygen is used as the terminal acceptor of the electrons extracted from food molecules. The capacity to use oxygen to oxidise nutrients, such as glucose and fatty acids, yields a substantially greater amount of energy than does fermentation. The chapter recounts the accumulation of atmospheric O2 on Earth about 2 billion years ago, when existing organisms were confronted with a serious problem: molecular oxygen forms toxic oxygen ions and peroxides called reactive oxygen species (ROS). ROS react with and damage or destroy biomolecules. Consequently, exposure to O2 acted as a severe selection pressure.
Chapter
Aerobic Metabolism I: The Citric Acid Cycle
Chapter
Reactive oxygen species, reactive nitrogen species and redox signalling
This chapter explains our current understanding of how reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated and perceived, and how they propagate their messages. It argues that the main components involved here include those used in phosphorylation and cyclic nucleotides. The chapter also explains that ROS and RNS are in control of a host of cellular functions. It emphasizes that ROS and RNS are now known to be important as signals in many biological systems, including prokaryotes, animals, and plants. Lastly, the chapter considers redox signalling and molecular mechanisms of hydrogen peroxide signalling.
Chapter
Abiotic Stresses and How They Affect Crop Yield
Maarten J. Chrispeels
This chapter assesses abiotic stresses such as drought, floods, acidic soils, and soil salinity, and how they affect crop yield. Abiotic stresses cause plant cells to more highly express many genes that help the plant cope with the stress so that growth can continue, albeit at a slower rate. The formation of reactive oxygen species (ROS) is a response to many stresses. ROS damage cells but also serve as signals and cause cells to turn on stress-response genes. The chapter then considers water potential, which is the physical property of water that drives water movement from the soil through the plant and into the atmosphere. It also looks at how some common agricultural practices, other human activities, and climate change are leading to soil degradation and increased abiotic stresses.
