Photosynthesis: Molecular, Physiological and Environmental Processes

Rating:
Summary: A concentrated overview of photosynthesis
Review: It is perhaps a cliche to say that the process of photosynthesis is the most important one on Earth. Taking advantage of an essentially inexhaustible source of photons, photosynthesis is a highly complex sequence of physical events, with its evolutionary origins only recently explained. This monograph gives a comprehensive overview of photosynthetic system, and is one of the few that includes discussion of its molecular biology. The genetic engineering of the chloroplast is now of great interest, and is being done by many researchers. Readers who want to understand these developments will find a good start in this book. In addition, there has been a growing interest in being able to emulate photosynthesis in non-biological systems. Called `artificial photosynthesis', it would replicate or perhaps improve on the natural photosynthetic system, a prospect that has tremendous technological implications. In addition, the physics behind photosynthesis is discussed at an elementary level in the book, and would be suitable for readers who want to understand the physical processes but without getting into the details. A more detailed discussion would require a discussion of the physics of `excitons', which can involve advanced mathematics, more than this book wants to provide. Unfortunately the book does not discuss how the photosynthetic apparatus evolved, but this is a recent topic that was still pretty much an open question at the time of its publication.

Every topic in the book is fascinating, but for this reviewer the chapter on the molecular biology of the photosynthetic system stood out among the rest. One learns of how the chloroplasts contain DNA that replicates independently of other parts of the genome. This is called `chloroplastic DNA (cpDNA)' and codes for certain proteins, a list of which is given in the chapter. It is interesting to note that chloroplasts supposedly originated as prokaryotic endosymbionts, but as the author explains, many of the original symbiont genes were transferred to the nuclear genome. Their function was then replaced by new mechanisms in the chloroplasts. Chloroplast genes can be activated by light. Called in the book `photogenes', when illuminated they result in increases in transcripts and protein products. A list of light activated genes of the chloroplast and their products are given in this chapter.

In this chapter, the author also points out some open problems that require further research, such as the mechanism behind the proteolysis of the D1 protein in photosystem II. Another open question regards finding the explanation as to why different species of plants have wide variations in their response to light, with genes in some species showing both low and normal response to light, whereas in another showing no low light response. The author's tentative explanation for these differences is that they originate in the context of the ecological behavior of the plants. The sensitivity to light may give an advantage when seedlings are attempting to reach the soil surface or are in deep shade. It would not be advantageous to initiate the photosynthetic reactions fully until sufficient light is available.

That the nuclear and chloroplast genomes are not independent is readily clear from the discussions in this chapter on their interaction. The author gives a detailed diagram illustrating how they interact in terms of their gene products and their incorporation into the chloroplast compartments. The role of phytochrome in the regulation of gene expression is emphasized throughout this discussion. The author also discusses the `chloroplast factor', which is a mechanism for passing information to the nucleus that the chloroplast is ready to receive a protein.

This short review does not even scratch the surface of the many topics that are discussed in this book. Indeed, the apparatus of photosynthesis is extremely complex and one must spend a fair amount of time in attempting to understand it with a reasonable scale of detail. Many references are given for those readers who intend to gain an even more detailed understanding of photosynthesis. The time spend reading and studying this book is well worth it, even if one does not intend to specialize in research in photosynthesis, but rather has an intense curiosity to fathom what is certainly one of the most fascinating of physical systems to evolve on this planet.