The evolution of photosynthesis and chloroplasts

This review focuses on what has been learned about the evolution of photosynthesis in the past five years, and omits evolution of CO2 assimilation. Oxygenic photosynthesis (using both photosystems I and II) has evolved from anoxygenic photosynthesis. The latter occurs in different variants, using either a type 1 photosystem resembling photosystem I, or a type 2 photosystem resembling photosystem II. Opinions differ as to how two types of photosystem came to be combined in the same organism, whether by gene transfer between bacteria, by fusion of bacteria, or as a result of gene duplication and evolution within one kind of bacterium. There are also different opinions about when oxygenic photosynthesis arose, in conjunction with the Great Oxygenation Event, 2.3 billion years before the present, or more than a billion years before that. Cyanobacteria were the first organisms to carry out oxygenic photosynthesis. Some of them gave rise to chloroplasts, while others continued to evolve as independent organisms, and the review outlines both lines of evolution. At the end we consider the evolution of photosynthesis in relation to the evolution of our planet

Evolution of the Z-Scheme of Electron Transport in Oxygenic Photosynthesis

We start with the discussion of the photosynthetic unit, based on the experiments of Emerson and Arnold (1932a, 1932b), continue with the first two-quantum proposal by Rabinowitch (1945, 1956), Emerson's Red drop (1943) and Emerson Enhancement Effect (1957) and various action spectra made for understanding the roles of the photosynthetic pigments. The experimental work of Kok (1959) and the theoretical model by Hill and Bendall (1960) were followed soon thereafter by the seminal papers of Duysens et al. (1961) and Duysens and Amesz (1962), in which the two photosystems were shown to be connected, in series, by cytochrome, which can be photooxidized by photo system I and photoreduced by photosystem II. Further, Witt et al. (1961) and others, cited in this paper, made refinement of the Z-scheme

In photosynthesis, oxygen comes from water: from a 1787 book for women by Monsieur De Fourcroy

Abstract It is now well established that the source of oxygen in photosynthesis is water. The earliest suggestion previously known to us had come from René Bernard Wurmser (1930). Here, we highlight an earlier report by Monsieur De Fourcroy (1787), who had already discussed the broad outlines of such a hypothesis in a book on Chemistry written for women. We present here a free translation of a passage from this book, with the original text in French as an Appendix

Light quality, oxygenic photosynthesis and more.

Oxygenic photosynthesis takes place in thylakoid membranes (TM) of cyanobacteria, algae, and higher plants. Itbegins with light absorption by pigments in large (modular) assemblies of pigment-binding proteins, which thentransfer excitation energy to the photosynthetic reaction centers of photosystem (PS) I and PSII. In green algaeand plants, these light-harvesting protein complexes contain chlorophylls (Chls) and carotenoids (Cars). However,cyanobacteria, red algae, and glaucophytes contain, in addition, phycobiliproteins in phycobilisomes that are attachedto the stromal surface of TM, and transfer excitation energy to the reaction centers via the Chl a molecules in the innerantenna of PSI and PSII. The color and the intensity of the light to which these photosynthetic organisms are exposedin their environment have a great influence on the composition and the structure of the light-harvesting complexes(the antenna) as well as the rest of the photosynthetic apparatus, thus affecting the photosynthetic process and even theentire organism. We present here a perspective on ‘Light Quality and Oxygenic Photosynthesis’, in memory of GeorgeChristos Papageorgiou (9 May 1933–21 November 2020; see notes a and b). Our review includes (1) the influence ofthe solar spectrum on the antenna composition, and the special significance of Chl a; (2) the effects of light quality onphotosynthesis, measured using Chl a fluorescence; and (3) the importance of light quality, intensity, and its durationfor the optimal growth of photosynthetic organisms

The evolution of photosynthesis and its environmental impact

Photosynthesis in plants is a very complicated process, utilizing two photosystems in series to carry out the very energy-demanding process of oxidizing water to molecular oxygen and reducing carbon dioxide to organic compounds. The first photosynthetic organisms, living more than 3.4, perhaps even 3.8 Ga, i.e. American billion (109) years ago, carried out a simpler process, without oxygen production and with only one photosystem. A great variety of such one-photosystem photosynthesizers are living even today, and by comparing them, and from chemical fossils, researchers are trying to piece together a picture of the course of the earliest evolution of photosynthesis. Chlorophyll a probably preceded bacteriochlorophyll a as a main pigment for conversion of light into life energy. The process of carbon dioxide assimilation, today taking place mainly in conjunction with photosynthesis, is even older than photosynthesis itself. Oxygenic photosynthesis, i.e. photosynthetic production of molecular oxygen, first appeared in ancestors of present-day cyanobacteria more than 2.7, perhaps already 3.7 Ga ago. Cyanobacteria entered into close association with other organisms more than 1.2 Ga ago, and chloroplasts in green algae and green plants as well as those in algae on the "red" line of evolution (red algae, cryptophytes, diatoms, brown algae, yellow-green algae and others) stem from a single early event of endosymbiotic uptake of a cyanobacterium into a heterotrophic organism. Only ecologically unimportant exceptions from this rule have been found. The chloroplasts on the "red line", excepting those of red algae, stem from a single event of secondary endosymbiosis, in which a red alga was taken up into another organism. There are also examples of tertiary (third level) endosymbiotic events. Thylakoids in land plants are partially appressed and forming grana, while those of, e.g., red algae do not have this structure, and this difference can be explained by the different spectra of ambient light. At the end of the chapter a brief review is given of the evolution of the assimilation of carbon dioxide, the adaptation to terrestrial life, and the impact of photosynthesis on the terrestrial environment

Detectability of life and photosynthesis on exoplanets.

‘Is there life on exoplanets?’. We refer to exoplanets as planets in other solar systems than our own. This often asked question can be further refined by asking ‘is there life on exoplanets which is so extensive that it may impact on its atmosphere, its biosphere and its optical properties?’. And if such a life exists, at astronomical distances from us, can we detect it with instruments on Earth-based or Earth-orbiting observatories? Will then, in that case, our advanced knowledge of present-day and early-day photosynthesis on Earth help us select appropriate biosignatures that may signal its presence? Here we elaborate further on these themes, based on the most recent literature, and from the point of view of photosynthesis. We also provide our considered views. Although search for chlorophyll is considered desirable, we conclude that our best bet is to look for and analyse photosynthesis-related gases, namely O2, CO2 and H2O vapour. We shall keep in mind that the evolutionary tree of life on our planet has its roots in autotrophy, and of the various forms of autotrophy, only oxygeni