Phosphate transport of fungi to plant roots requires proton pump
Just like the transport proteins mentioned above, this proton pump is localized in the periarbuscular membrane. There, it transports protons - small positively charged hydrogen ions – into the space between the periarbuscular and the fungal membrane. This leads to a higher concentration of protons on the outside of the plant cell than on the inside, a so-called proton gradient. The protons on the outside serve as energy source for the transport of phosphate into the plant cell.
No proton pump – no phosphate
To prove that this proton pump is required to transport phosphate, the scientists generated Medicago truncatula mutants that have a non-functional version of the respective gene. Thus, the proton pump cannot be synthesized correctly. The symbiotic phosphate uptake and the growth rate of those mutants were compared to wild type plants. Roots of both plants - mutant and wild type - were equally colonized by Rhizophagus irregularis. Nevertheless, under phosphate deprivation the wild type plants grew better than the mutants due to the extra P-supply from the fungus.
The scientists also compared the phosphate transport to different parts of the plants. Wild type plants incorporated fungal phosphate in roots and shoots, as usual for mycorrhizal symbiosis. But, this pattern of phosphate incorporation could not be observed for the mutants. “We discovered that the proton pump is essential for phosphate transport”, Franziska Krajinski says, “The mutants could not grow on phosphate depleted soil, although they were colonized by the fungus”. Considering the declining phosphate resources, it is crucial to build a better understanding of symbiotic processes. The use of mycorrhizal products as replacement for mineral fertilizers is restricted to organic farming at the moment. Though, this will probably get increasingly important for the nutrition of crop plants and our own nutrition as well in the future.
More information, Prof. Dr. Krajinski's Website: http://www.mpimp-golm.mpg.de/8316/2krajinski
Original publication: http://www.plantcell.org/content/early/2014/04/29/tpc.113.120436.abstract?sid=0e
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