Tansley Review No. 112

Abstract

I. INTRODUCTION 360 II. PHOTOINHIBITION AND ACTIVE OXYGEN 360 III. OXYGEN AS AN ELECTRON ACCEPTOR 362 1. Oxygen‘poises’electron transport and carbon assimilation 362 2. The role of oxygen in ATP synthesis 364 3. How fast is O2reduction at PSI? 364 4. Chloroplastic processing of H2O2 366 IV. REDOX REGULATION OF PHOTOSYNTHETIC METABOLISM 368 1. The thioredoxin system 368 2. Manipulating the expression of thiol‐regulated enzymes 369 3. Modifying sensitivity to thiol regulation 369 V. PHOTORESPIRATION 369 1. The pathway and its genetic manipulation 369 2. Engineering plants that photorespire less? 371 3. Is photorespiration important in energy dissipation? 372 4. Production and processing of photorespiratory H2O2 373 5. Catalase and foliar H2O2levels 374 6. Catalase and non‐photorespiratory H2O2generation 375 VI. RESPIRATION 376 1. ‘Photosynthetic’respiration 376 2. AOS in the mitochondrion 376 3. AOX: regulation and significance to photosynthesis 377 VII. PHOTOSYNTHESIS AND REDOX SIGNAL TRANSDUCTION 378 1. The need for sensors, signals and transducers 378 2. Signal transduction at the local level 378 3. Remote signalling and responses leading to acclimation of photosynthesis? 379 4. Interactions between AOS, NO., and antioxidants 380 VIII. CONCLUSIONS 380 Acknowledgements 381 References 381 The gradual but huge increase in atmospheric O2 concentration that followed the evolution of oxygenic photosynthesis is one consequence that marks this event as one of the most significant in the earth's history. The high redox potential of the O2/water couple makes it an extremely powerful electron sink that enables energy to be transduced in respiration. In addition to the tetravalent interconversion of O2 and water, there exist a plethora of reactions that involve the partial reduction of O2 or photodynamic energy transfer to produce active oxygen species (AOS). All these redox reactions have become integrated during evolution into the aerobic photosynthetic cell. This review considers photosynthesis as a whole‐cell process, in which O2 and AOS are involved in reactions at both photosystems, enzyme regulation in the chloroplast stroma, photorespiration, and mitochondrial electron transport in the light. In addition, oxidants and antioxidants are discussed as metabolic indicators of redox status, acting as sensors and signal molecules leading to acclimatory responses. Our aim throughout is to assess the insights gained from the application of mutagenesis and transformation techniques to studies of the role of O2 and related redox components in the integrated regulation of photosynthesis.

A Ratiometric Sensor Using Single Chirality Near‐Infrared Fluorescent Carbon Nanotubes: Application to In Vivo Monitoring

“…Furthermore, NO is a signaling molecule in plants [ 25 ] whereas H 2 O 2 is an indicator of oxidative stress that can damage the plant's photosynthetic machinery. [ 26 ] For each species, we identify unique corona phases that are selective to each analyte, and pair them with a corona phase that is largely invariant to that analyte by using RACES. The result, for each case, is a pair of SWCNT fl uorescence emitters, where only one is modulated in response to an analyte and the other signal acts as a reference, allowing absolute calibration independent of overall intensity, a clear advance from a multichirality approach.…”

Light and Oxygen Are Not Required for Harpin-induced Cell Death

“…The photosynthetic electron transfer chain (ETC) in the chloroplasts is the major site of ROS generation in photosynthetic cells. Thus, light and chloroplast-based reactions as well as the associated process of photorespiration are considered to have a predominant role in cellular redox regulation (8,9). Exposure to abiotic stresses, such as drought, frequently causes inhibition of photosynthesis and accelerated ROS production (10).…”

Effects of elevated atmospheric CO 2 concentration on leaf dark respiration of Xanthium strumarium in light and in darkness

“…Although the light reaction in photosynthesis provides ATP and reductants for biosynthesis in a leaf cell during illumination, mitochondrial respiration in light is necessary for biosynthetic reactions in the cytosol, such as sucrose synthesis (1,2). Respiratory activity in light can even be considered part of the photosynthetic process, because it is needed to regulate the state of stromal redox during photosynthesis (3) and to maintain the cytosolic ATP pool (1). Mitochondrial respiration might also be a source for biosynthetic precursors, such as acetyl-CoA or acetate for chloroplastic fatty acid synthesis in light (1).…”

“…The lower rate of nonphotorespiratory mitochondrial CO 2 release during illumination has been interpreted as evidence for partial inhibition of leaf respiration by light (4)(5)(6). The magnitude of light inhibition of respiration seems to depend on the photosynthetic capacity (1), but the mechanism of light regulation of mitochondrial respiration is not clearly understood (2,3). Although there has been much study of, albeit little agreement on, the effects of elevated CO 2 on plant respiration (7)(8)(9), the effects of elevated CO 2 on mitochondrial respiration in light have been little studied and hence are largely unknown (5, 10).…”