Photosynthesis/Addendum

Selected article abstracts bulleted

Evolution of Photosynthesis

"Evolution of Photosynthesis"

• Energy conversion of sunlight by photosynthetic organisms has changed Earth and life on it.
• Photosynthesis arose early in Earth’s history, and the earliest forms of photosynthetic life were almost certainly anoxygenic (non-oxygen evolving).
• The invention of oxygenic photosynthesis and the subsequent rise of atmospheric oxygen approximately 2.4 billion years ago revolutionized the energetic and enzymatic fundamentals of life.
• The repercussions of this revolution are manifested in novel biosynthetic pathways of photosynthetic cofactors and the modification of electron carriers, pigments, and existing and alternative modes of photosynthetic carbon fixation.
• The evolutionary history of photosynthetic organisms is further complicated by lateral gene transfer that involved photosynthetic components as well as by endosymbiotic events.
• An expanding wealth of genetic information, together with biochemical, biophysical, and physiological data, reveals a mosaic of photosynthetic features.
• In combination, these data provide an increasingly robust framework to formulate and evaluate hypotheses concerning the origin and evolution of photosynthesis.

"Functional Evolution of Photochemical Energy Transformations in Oxygen-Producing Organisms"

• Chlorophyll a is the photochemical agent accounting for most oxygenic photosynthesis, that is, over 99.9% of photosynthetic primary activity on Earth.

• The spectral and energetic properties of chlorophyll a can, at least in part, be rationalised in terms of the solar spectral output and the energetics of oxygen production and carbon dioxide reduction with two photochemical reactions.

• The long wavelength limit on in vivo chlorophyll a absorption is probably close to the energetic limit: longer wavelengths could not support a high rate and efficiency of oxygenic photosynthesis.

• Retinal, a b-carotene derivative that is the chromophore of rhodopsin, acts not only as a sensory pigment, but also as an ion-pumping photochemical transducer.

• Both sensory and energy-transforming rhodopsins occur in oxygenic phototrophs, although the extent of expression and the function of the latter are not well understood.