Evolution of Chlorophyll Biosynthesis—The Challenge to Survive Photooxidation

ation of mechanisms that confer photoprotection on *Institute for Plant Sciences plants is particularly important because it may provide Department of Genetics the basis for the construction of new, porphyrin-based Swiss Federal Institute of Technology Zurich (ETH) photobleaching herbicides to be exploited in modern ETH-Zentrum weed control. It is the aim of this review to summarize Universitätsstrasse 2 current ideas on the evolution of chlorophyll biosynthe-CH-8092 Zurich sis in a quest to explain how early photosynthetic organ-Switzerland isms acquired the capability to solve the problem of † A. N. Bakh Institute of Biochemistry photooxidation. Russian Academy of Sciences Photoprotection—How Plants Avoid Leninsky pr 33 " Self-Poisoning " with Oxygen Moscow 117071 in the Presence of Light Russia Photosynthetically active organisms are continuously forced to cope with the problem of photooxidation under the aerobic conditions of our current atmosphere on Light is of fundamental importance for life on earth. Earth. Not only the end products, chlorophylls a and b, Through photosynthesis, light ultimately provides the but also many intermediates in the biosynthetic pathway sole source of energy for the growth and development of porphyrins, such as protoporphyrin IX and its various of almost all living organisms. The ability to harvest and Mg 21 derivatives, including protochlorophyllide, tend to to convert the sunlight into chemical energy to be con-interact after light absorption in an uncontrolled manner served in ATP and NADPH 2 is one of the most striking with other macromolecules in their environment. Instead characteristics of plant organisms. It is based on the of transferring their excitation energy onto their ultimate evolution of sophisticated light absorption and energy targets, the excited porphyrin pigments, by triplet–triplet transduction mechanisms. In higher plants, chlorophylls interchange, interact with oxygen to produce singlet (chlorophyll a plus chlorophyll b) are involved in these oxygen. This compound is potentially harmful to the processes. Most other photosynthetically active organ-plant because it causes membrane peroxidation, protein isms, such as the Chloroflexaceae, many purple bacteria denaturation, and pigment bleaching, effects that col-(proteobacteria), including Rhodobacter capsulatus, lectively lead to photooxidative damage of the chloro-and the green sulfur bacteria, such as Chlorobiaceae, plast, the site of porphyrin synthesis, and ultimately to all contain a different porphyrin compound, bacteriochl-cell death. orophyll a, in their reaction centers. In higher plants such as angiosperms, several differ-Chlorophyll and bacteriochlorophyll are structurally ent photoprotection mechanisms operate. During pho-related porphyrin compounds (Figure 1). Most of the tosynthesis, excited chlorophyll …