Two chlorophyll fluorescence components also were resolved: the short-wavelength component originated primarily from photosystem II and was most intense near the periphery of the cell; and the long-wavelength component that is attributed to photosystem I, because it disappears in mutants lacking this photosystem, was of higher relative intensity toward the inner rings of the thylakoids. Together, the results suggest compositional heterogeneity between thylakoid rings, with the inner thylakoids enriched in photosystem I.
Vermaas said this means that even in a simple and small cyanobacterial cell (about a hundred fold smaller than can be seen by the human eye) there is an exquisite functional division of labor between membranes inside the cell, with different processes in photosynthesis in different areas of the membranes.
We found that the two photosystems are not fully co-localized in thylakoids in the cell, even though thylakoids look all the same in electron micrographs, Vermaas said. Based on this, the way the cells probably work, is that the inner thylakoids primarily make ATP (adenosine triphosphate), the energy currency of the cell, by cyclic electron transport around photosystem I, and the peripheral ones do linear electron flow resulting in ATP as well as reduced nicotinamide adenine dinucleotide phosphate, the carrier of reducing equivalents used for carbon dioxide fixation.
The bottom line here is that even if cell compartments, like thylakoid membranes, cannot be distinguished in an electron microscope, there is a functional heterogeneity, because of different protein complexes in different parts of the thylakoids, he explained. This heterogeneity had long been suspected, but never been proven experimentally.
These results show that hyperspectral fluorescence imaging can provide new information regarding pigment organization and localization even in small cells, and provides a new approach in in
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Arizona State University