Biological complexity: how photosynthesis controls electrons (Introduction)

by David Turell , Friday, January 10, 2020, 03:26 (1780 days ago) @ David Turell

A very complex new aspect of photosynthesis regulation is found:

https://phys.org/news/2020-01-ancient-iron-sulfur-based-mechanism-electron-photosynthes...

"[Research] professor[s] of biochemistry, have shown that the chloroplast sensor kinase (CSK) protein is equipped with an evolutionarily conserved iron-sulfur cluster. The cluster helps it to sense the presence of electrons and thereby send signals to the gene expression machinery in plant chloroplasts to turn photosystem genes on and off.

"'CSK is an ancient protein found in both cyanobacteria and chloroplasts. More than a billion years ago a cyanobacterium took up residence inside a eukaryotic host cell and became the chloroplast of plants and algae," Puthiyaveetil said. "By examining the cyanobacterial, plant and diatom CSK proteins, we've discovered that CSK uses an iron-sulfur cluster to sense the electron transport, assessing how well the electrons are flowing, and make adjustments in the relative abundance of plant photosystems to keep photosynthesis working correctly and protect the plant from oxidative stress."

***

"During photosynthesis, plants turn sunlight into energy via two photosystems. Photosystem I utilizes long wavelength light efficiently while photosystem II prefers mostly short wavelength light, with the two photosystems connected by the plastoquinone pool. As the systems work, photosystem II sends electrons into the plastoquinone pool while photosystem I removes and utilizes them.

"But if a plant is exposed to shorter wavelength light, the electron balance can be lost. In that case, photosystem II would send electrons into the plastoquinone pool, but photosystem I wouldn't be able to draw them efficiently. Those electrons could linger in the plastoquinone pool and produce dangerous free radicals.

"'The two photosystems are like two photovoltaic cells connected in series," Puthiyaveetil said. "They should convert light energy at equal rates for optimal electron transport. If the electron transport is not balanced, you get free radicals that can damage the plant's photosynthetic machinery and hurt or kill the plant."

"Purdue scientists determined that CSK's iron-sulfur cluster acts as a sort of magnet for those extra electrons. When the plastoquinone pool becomes reduced, meaning it has excess electrons, those electrons leak into CSK and turn off its kinase activity.

"When kinase activity is interrupted, CSK stops transferring phosphate groups to the chloroplast gene expression machinery, turning on photosystem I genes and increasing its amount and therefore activity in short wavelength light. In essence, when CSK's kinase activity is on, it serves as a brake pedal for photosystem I gene expression.

"The CSK is redox-reactive, meaning it's using the iron and sulfur to sense the electron flow, and that's keeping the two photosystems working at the same rate in photosynthesis.

"The findings illuminate an elegant regulatory mechanism in the photosynthetic processes of plants. It's possible, Puthiyaveetil said, that one day this regulatory circuit could be modified to increase photosynthetic efficiency in crop plants by improving light capture in shaded conditions." (my bold)

Comment: Photosynthesis is a vital source of the level of oxygen now present in this atmosphere. Without it evolution could not have passed beyond the very small animal stage.
Note my bold: without this precise regulatory system photosynthesis would not work. It is so complex is cannot be built by step by step testing of each advance, that is, it is irreducibly complex, a logical concept introduced by Dr. Behe, one of the leading scientists in the ID group, of whom there are many with important papers in publication. Such design requires a designing mind behind it to create it all at once. Any Darwin approach fails to explain it. How long would it take to develop it by chance?