|Demmig-Adams, Barbara - U OF COLORADO, BOULDER|
|Adams, William - U OF COLORADO, BOULDER|
Submitted to: Complete Book
Publication Type: Book / Chapter
Publication Acceptance Date: February 13, 2006
Publication Date: April 7, 2006
Citation: Demmig-Adams, B., Adams, W.W., Mattoo, A.K. 2006. Photoprotection, photoinhibition, gene regulation, and environment. Springer, Germany, 380 p. Technical Abstract: Photosynthesis is integral to plant productivity, both as a source of energy and materials and as a target for feedback regulation by the demand of the whole plant for photosynthate. Photosynthesis is also strongly modulated by the environment; multiple environmental conditions result in the absorption of potentially harmful levels of excess light. Photoprotection and the phenomenon of photoinhibition of photosynthesis are thus key responses of plants to the environment as well. However, it remains unknown whether photoinhibition decreases or increases plant survival, fitness, and productivity. Similarly, interactions among different components of the photoprotective antioxidant network and their roles in cellular signaling and gene expression remain to be fully elucidated. This volume brings together contributions from widely different areas in the hope of stimulating future research. Several concepts are emphasized in this volume. One is that chloroplast defenses against oxidative stress and excess reactive oxygen production are highly integrated with each other and are in communication with the cellular antioxidant network. Furthermore, it is increasingly recognized that antioxidants have a crucial role in redox sensing and signaling, in addition to their role in protecting the integrity of the chloroplast. This is highly significant since cellular redox balance participates in the modulation of a host of key responses in growth and development, such as the regulation of the cell cycle, senescence, and programmed cell death. This volume combines contributions on photoinhibition and photoprotection with those on redox signaling and gene modulation to integrate photoprotective responses into 'the bigger picture'. We bring together the full continuum of processes from protection on one hand to senescence and cell death at the other extreme. Specific topics covered here include perspectives on the historic development of this research area. Photoprotective thermal dissipation of excess excitation energy is reviewed and its relationship to photoinhibition discussed. What role does photoinhibition play in plant survival, fitness, and productivity? Where does photoinhibition fit into the continuum of plant responses - from photoprotection by a cascade of defense mechanisms to cell death? During seasons with extreme conditions, such as icy winters or scorching, dry summers, the primary reactions of photosynthesis can become disabled. Many studies focus on the inactivation of the photosystem II core protein D1 seen during photoinhibition, and it is currently widely assumed that this inactivation represents damage. However, much of what has been assumed to be damage to chloroplast processes may, in fact, be caused by genetic programs (Wagner et al. 2004, Science 306:1183). It is noteworthy that the plants exhibiting the greatest degree of photoinhibition of photosynthesis are perennial evergreens adapted to extreme environments. Is photoinhibition a limitation to plant productivity, or might it be a 'talent' of stress-tolerant species? In this volume, widely different views are expressed concerning these questions, making it clear that additional work is needed to resolve them. A wide range of environmental factors that affect photoprotection and photoinhibition is considered here: intense visible and ultraviolet light, winter conditions in temperate climates, nutrient deficiency, drought, and salinity. A molecular analysis of photoprotection is presented and the role of specific proteins in photoprotection is discussed. In addition to thermal dissipation pathways, alternative pathways for electron flow as well as the scavenging of reactive oxygen species by antioxidant metabolites (such as tocopherol, asccorbate, glutathione, xanthophylls) and enzymatic antioxidant pathways are reviewed. The peroxidation and recycling of lipids is considered together with the signaling functions of these reactions and of lipid-derived messengers. A comprehensive overview of the current understanding of signaling by reactive oxygen species and other signals that modulate gene expression is provided. Experimental approaches range from biochemical, physiological, genetic, and molecular approaches to field studies in a variety of natural environments.