Chlorophyll a Fluorescence: A Signature of Photosynthesis

Abstract

Why should a book on chlorophyll a (Chl a) fluorescence appeal to people who work on algae? At first sight there might seem to be a nexus between the two subjects. However, on reflection the two are intimately bound up. The algae are par excellence the great players in the field of photosynthetic pigments. After all, we still classify several groups of algae on their colouration. Just imagine if we tried to classify other protists in the same way! And whether they use red pigments, brown or green, all algae use Chl a as their central photochemical pigment. If you count cyanobacteria as algae there is now one possible exception to this rule: Acaryochloris marina (see below), where Chl d may totally replace Chl a. However, apart from that they all use Chl a. As a result the many types of other photosynthetic pigments in algae perform all kinds of dances with the central Chl a and the result is that by studying Chl a fluorescence one can learn a multitude of information that can be of help all the way from taxonomy, to productivity, to global warming. From the foregoing, it is therefore of no surprise that this is a large book. There are thirty-one chapters, by the world’s experts in the field, and the book weighs in at 2.2 Kg and covers 818 pages. This, unfortunately, is too many chapters to pick out each one for special mention, much as the high quality and interest of this book demands it. The book begins with two indispensable chapters by the Editors on the basics of fluorescence in photosynthetic organisms and its history. Luminescence, delayed light emission, goes back a long way; but not the word: it dates from 1897. Undoubtedly the ancients knew about bioluminescence from such things as fireflies, glow worms, particles in the sea (Noctiluca), fish, mushrooms and rotting meat, to name a few; but the ancients used the loose term “phosphorescence” (in various forms), and it is often difficult to pin down exactly what phenomenon was being referred to. Fluorescence, or prompt re-emission of light, is a much more recent word of Victorian origin; the phenomenon was first observed by Sir David Brewster in about 1834 and the word itself was coined by Sir G.G. Stokes in 1852 (from the mineral fluor-spar, which can be made to fluoresce). Based on the multiple associations that this word now conjures up, we have come a long way in 150 years! Many of the chapters in this book are for specialist interested in the physics and biophysics of fluorescence in photosynthetic apparatus, since the reaction centres of each and every photosystem and many of their light-harvesting proteins contain chlorophylls, which fluoresce. Thus there are chapters outlining the basic aspects of excitation energy migration, i.e., how the energy is distributed between the pigments, before fluorescence occur (R.M. Clegg) and trapping of excitation (R. van Grondelle; W.J. Vredenburg) and fluorescence in Photosystem I (S. Itoh and K. Sugiura). Other chapters which need not detain us here deal with such specialist areas as fluorescence in fruit and leaves (L. Nedbal and J. Whitmarsch), water stress (N.G. Bukhov and R. Carpentier), heavy metals toxicity (M.K. Joshi and P. Mohanty), light adaptation and senescence in plants (H.K. Lichtenthaler aand F. Babani) and a global analysis of fluorescence in plants (A Gilmore). Suffice it to say that few areas of interest to the eclectic reader are absent and what is present is of a very high standard.