Photoinhibition Of Photosynthesis

A comprehensive treatise on photoinhibition which provides an authoritative, up-to-date review of the important molecular, environmental and physiological issues.

A NATO Advanced Study Institute on "Light as Energy Source and Information Carrier in Plant Photo physiology" was held at Volterra, Italy, from September 26 to October 6, 1994, in order to consider the fundamental role that light plays in plant growth and development. This book summarises the main lectures given at this meeting which concentrated on both photochemical energy conversion and signalling (photosensing) aspects. Light harvesting and conversion into chemical energy in photosynthesis occurs at the level of chlorophyll/carotenoid containing photosystems in plants. Pigments are non covalently bound to a variety of polypeptides which serve as a specific scaffolding, necessary to determine the energy coupling between pigments and thus allowing rapid excitation energy trasfer from the antenna to the special reaction centre chlorophylls. Data from transient, time resolved spectroscopies, in the femtosecond and picosecond domain, together with model calculations, suggest that this process occurs in the 20-100 picosecond time span. The special ~ll u~ture of reaction centre complexes, ensures rapid primary charge separation, probably in the order of 1-3 picoseconds, with subsequent charge stabilisation reactions proceeding in the hundreds of picoseconds range. The recently resolved crystallographic structure of LHCII, the principal antenna complex of plants, allows precise determination of pigment-pigment distances and thus permits calculation of approximate chlorophyll-chlorophyll Forster hopping rates, which are in good agreement with time resolved measurements.

The process of the conversion of sunlight into food by plants (photosynthesis) is fundamental to all life on this planet. All students of biology need to understand this process in detail. This book treats photosynthesis in a simple methodical manner and explains complex concepts in an interesting and user-friendly way. It helps the student to think practically about the subjectand launches the reader towards the next stage in their understanding of plant biology.

The algae are a diverse group of organisms with forms that range in size from less than a micron in diameter to over ten meters in length. Small {laquo} 1 JLm diam) unicellular forms dominate the open waters of the oceans and large lakes. Large multicellular forms often form a large component of the autotrophic biomass of shallow waters at the periphery of lakes and oceans but have also been found on seamounts in clear open ocean waters at depths up to several hundred meters (Littler and Littler, 1985). Phytoplankton in the sea probably account for more than 50% of global photosynthesis, although there is considerable uncertainty about this estimate. In addition, many symbiotic associations between unicellu lar algae and heterotrophic or autotrophic organisms have been identi fied, and algae can be found in a diverse range of terrestrial environ ments, ranging from polar to desert regions. The most important common biochemical attribute that unites the algae is their ability to split water, producing molecular oxygen during photosynthesis and concomi tantly assimilating carbon dioxide. This attribute is shared with the terres trial plants, cyanobacteria and chloroxybacteria. Although vascular plants are excluded from this review, we employ a broad definition of algae that includes the photosynthetic, oxygenic procaryotes. Measurements of gas exchange are fundamental to most biochemical, physiological and ecological investigations of the algae.

Photoprotection, Photoinhibition, Gene Regulation, and Environment examines the processes whereby plants monitor environmental conditions and orchestrate their response to change, an ability paramount to the life of all plants. “Excess light”, absorbed by the light-harvesting systems of photosynthetic organisms, is an integrative indicator of the environment, communicating the presence of intense light and any conditions unfavorable for growth and photosynthesis. Key plant responses are photoprotection and photoinhibition. In this volume, the dual role of photoprotective responses in the preservation of leaf integrity and in redox signaling networks modulating stress acclimation, growth, and development is addressed. In addition, the still unresolved impact of photoinhibition on plant survival and productivity is discussed. Specific topics include dissipation of excess energy via thermal and other pathways, scavenging of reactive oxygen by antioxidants, proteins key to photoprotection and photoinhibition, peroxidation of lipids, as well as signaling by reactive oxygen, lipid-derived messengers, and other messengers that modulate gene expression. Approaches include biochemical, physiological, genetic, molecular, and field studies, addressing intense visible and ultraviolet light, winter conditions, nutrient deficiency, drought, and salinity.

This book covers the expression of photosynthesis related genes including regulation both at transcriptional and translational levels. It reviews biogenesis, turnover, and senescence of thylakoid pigment protein complexes and highlights some crucial regulatory steps in carbon metabolism.

These Proceedings comprise the majority of the scientific contributions that were presented at the VIIth International Congress on Photosynthesis. The Congress was held August 10-15 1986 in Providence, Rhode Island, USA on the campus of Brown University, and was the first in the series to be held on the North American continent. Despite the greater average travel distances involved the Congress was attended by over 1000 active participants of whom 25% were registered students. This was gratifying and indicated that photosynthesis will be weIl served by excellent young scientists in the future. As was the case for the VIth International Congress held in Brussels, articles for these Proceedings were delivered camera ready to expedite rapid publication. In editing the volumes it was interesting to re fleet on the impact that the recent advances in structure and molecular biology had in this Congress. It is clear that cognizance of structure and molecular genetics will be even more necessary in the design of experiments and the direction of future research.