The origin of chloroplasts

Although hardly relevant to the evolution of photosynthesis as such, the evolutionary origin of the chloroplast will be discussed first, because it provides a striking example of an evolutionary concept that explains a large number of observations which otherwise seem to make no sense at all. 

Globally speaking, photosynthesis takes place in the chloroplast and respiration takes place in the mitochondrion. Both chloroplasts and mitochondria are organelles of eukaryotic cells. They look in many respects like cells within the cell and 

In view of the endosymbiotic theory no further explanation is needed for the detailed similarity between mitochondrial respiration and that of some eubacteria, nor for the striking resemblance of chloroplast photosynthesis to that of cyanobacteria. 

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Some organisms, notably parasites, have organelles , which appear to be relics of chloroplasts but have no photosynthetic capacity. They are called apicoplasts but are probably not the origin of chloroplasts. Also note that a feature of symbiosis is that genes that are no longer required can be selectively lost as was probably the case in the example of loss from bacteria on becoming mitochondria (mentioned above). 

Soon after the discovery of triazine-resistant common groundsel, another equally important discovery was made. Radosevich and DeVilliers (1976) found that the mechanism of resistance in this weed was due to insensitive chloro-plasts that were capable of photosynthesis, even in the presence of simazine or atrazine. This was surprising because earlier research had confirmed that there were no differences in plant selectivity or susceptibility due to the origin of chloroplasts. Moreland (1969) had reported that isolated chloroplasts were equally inhibited to simazine whether they came from tolerant com or susceptible spinach. Radosevich and Appleby (1973) had confirmed there were no differences between the susceptible and resistant biotypes of common groundsel due to herbicide uptake, distribution, or metabolism, whereas it is known that com metabolizes triazine herbicides (Shimabukuro, 1985). 

Kishino, H., Miyata, T., and Hasegawa, M. (1990) Maximum likelihood inference of protein phylogeny and the origin of chloroplasts./o r a/ of Molecular Evolution, 31,151-160. 

Pacak, A. and Szweykowska-Kufinska, Z. (2000) Molecular data concerning alloploid character and the origin of chloroplast and mitochondrial genomes in the liverwort Pellia borealis. Journal of Plant Biotechnology, 2 101-108. 

Extensive RNA editing of U to C in addition to C to U substitution in the rbcL transcripts of hornwort chloroplasts and the origin of RNA editing in green plants." ... 

Spooner, D. M., Nunez, J., Rodriguez, F., Naik, P. S., Ghislain, M. (2005b). Nuclear and chloroplast DNA reassessment of the origin of Indian potato varieties and its implications for the origin of the early European potato. Theor. Appl. Genet., 110,1020-1026. 

Henick-Kling, T. (1995). Control of malo-lactic fermentation in wine Energetics, flavour modification and methods of starter culture preparation. J. Appl. Bacteriol. 79, 29S-37S. Imazio, S., Labra, M., Grassi, F., Scienza, A., and Failla, O. (2006). Chloroplast microsatellites to investigate the origin of grapevine. Genet. Resour. Crop Evol. 53,1003-1011. 

Whatley et al. (1979) in an overview of the origins of mitochondria and chloroplasts raised the possibility that hydrogenosomes arose through an independent endosymbiotic event. This idea agreed well with our thinking at the time and I embraced it wholeheartedly. In my review of 1980 I discussed this problem as follows ... 

The transition from prokaryotic to eukaryotic cells and the subsequent events that took place during the origin of the eukaryotic cell remain some of the greatest unresolved, and hotly debated, biological puzzles. One of the few widely accepted facts of early eukaryotic evolution is that eukaryotic cells are fundamentally chimaeric organelles such as mitochondria and chloroplasts are derived from endosymbiotic precursors that are... 

It is not improbable that further investigation of PolyP metabolism in mitochondria and chloroplasts would reveal novel features of similarity with eubacteria in favour of the endosymbiotic theory of the origin of eukaryotes. 

Other than in prokaryotic cells which lack mitochondria and chloroplasts, manganese superoxide dismutases are apparently restricted to the above two organelles in eukaryotic cells (51, 52) this forms strong support for the symbiotic hypothesis for the origin of mitochondria and chloroplasts (53, 54). Kinetic studies of superoxide dismutation by these enzymes indicate three oxidation states of Mn (presumably divalent, trivalent, and tetravalent) are involved in the catalytic cycle (57, 58). They also show that a Mn-02 complex may conceivably be formed. Well-characterized Mn-dioxygen (i.e., 02,02 , 022 ) adducts are extremely rare, the first structurally characterized example being reported only in 1987 (60). 

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