Biological complexity: photosynthesis energy controls (Introduction)

by David Turell @, Tuesday, June 30, 2020, 20:02 (12 days ago) @ David Turell

Another study increases the knowledge of the overwhelming complexity involved:

"Photosynthesis utilizes light as an energy source for plant chloroplasts to synthesize carbohydrates from water and CO2 molecules. ATPplays an important role in this process, as it promotes plant growth and supply energy for various cellular activities. It had been a general belief that mature plant chloroplasts can import ATP from cytosol since 1969, but it was shown to be untrue by Dr. Lim and his team in 2018, through introducing a novel ATP sensor in the subcellular compartments of a C3 model plant, Arabidopsis thaliana. This finding has revised our understanding on chloroplast bioenergetics during daytime and nighttime and how mature chloroplasts optimize energy efficiency.

"Another unresolved problem in photo-energy is that the source of NADH as a fuel for mitochondria (the major ATP synthesizing organelle in cells) to produce ATP during photosynthesis is unclear. Some researchers suggested that excess reducing equivalents carried by surplus NADPH (Reduced Nicotinamide adenine dinucleotide phosphate) can be exported to the cytosol in the form of malate, which can then enter mitochondria through the malate-OAA shuttle, and converted into OAA and NADH in the mitochondrial matrix.

"On the other hand, some researchers proposed that during photorespiration glycine decarboxylase generates a large amount of NADH in mitochondria for ATP production and surplus reducing equivalents carried by NADH is exported by the mitochondrial malate-OAA shuttle to the cytosol.


"...we found that photorespiration supplies a large amount of NADH to mitochondria during photosynthesis, which exceeds the NADH-dissipating capacity of the mitochondria. Consequently, the surplus NADH must be exported from the mitochondria to the cytosol through the mitochondrial malate-OAA shuttle," said Ms Sheyli Lim, a Ph.D. student and the first author of a manuscript published in Nature Communications. "Solving this question allows us to understand more about the energy flow between chloroplasts and mitochondria during photosynthesis, which could help us to booth the efficiency of photosynthesis in the future."

Comment: It is difficult to follow this verbiage without looking at the diagram which I cannot reproduce here. Only a designer could produce this complex system.

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