Biological complexity:photosynthesis controls (Introduction)

by David Turell , Monday, July 17, 2017, 22:27 (2686 days ago) @ David Turell

Too much sunlight can cause an over reactive photosynthetic process and damage the plant. There are built in controls:

https://phys.org/news/2017-07-reveals-mechanisms-protein-moss-green.html

"Photosynthesis, which allows energy from the sun to be converted into life-sustaining sugars, can also be hazardous to green plants. If they absorb too much sunlight, the extra energy destroys their tissue.

"To combat this, green plants have developed a defense mechanism known as photoprotection, which allows them to dissipate the extra energy. Researchers from MIT and the University of Verona have now discovered how the key protein in this process allows moss and green algae to protect themselves from too much sun.

"The researchers found that the protein, embedded in the membranes in the chloroplast, can switch between different states in response to changes in sunlight. When moss and green algae absorb more sunlight than they need, this protein releases the energy as heat, preventing it from building up and damaging the cells. The protein can act within seconds of a change in sun exposure, such as when the sun appears from behind a cloud.

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"Most plants absorb far more sunlight than they can actually use. In very sunny conditions, they convert only about 30 percent of the available sunlight into sugar, while the rest is released as heat.

"Under sunny conditions, the plants have energy sitting around that is too much for the capacity of the rest of the molecular machinery," Schlau-Cohen says.

"If this energy is allowed to remain in the plant cells, it creates harmful molecules called free radicals that can damage proteins and other important cellular molecules.

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"It was discovered several years ago that a protein called light-harvesting complex stress-related 1 (LHCSR1) is the major player in photoprotection that occurs over short timescales (seconds to minutes) in green algae and moss. This protein is embedded in the membranes in the chloroplast and interacts with chlorophyll and carotenoids, another type of light-absorbing pigment. However, the mechanism of how this photoprotection works was not known.

"Under cloudy or shady conditions, LHCSR1 simply absorbs photons and passes the energy on into the rest of the photosynthetic machinery. When the sun comes out and energy intake rises, LHCSR1 switches to another conformation within seconds. This switch is caused by a decrease in pH, which occurs when too many hydrogen ions are generated by water-splitting during photosynthesis.

"When this occurs, the protein becomes locked into a rigid structure that allows it to convert more of the absorbed light energy into heat, through a mechanism that is not fully known.

"Photoprotection can also be turned on more gradually by another feedback mechanism involving pH. A decrease in pH activates an enzyme that changes the molecular composition of a carotenoid that interacts with LHCSR1. This leads the protein to favor and stabilize its photoprotective state.

"Both of these states are controlled by a feedback loop within the organism. The pH is a short timescale response, and the molecular composition is a longer timescale response," Schlau-Cohen says." (my bold)

Comment: Once again we see a complex mechanism controlled by a feedback loop. This complex mechanism had to be developed in one step or the plants would have destroyed themselves. Again saltation designed by God.