%0 Journal Article %1 RN967 %A Babst, B. A. %A Braun, D. M. %A Karve, A. A. %A Baker, R. F. %A Tran, T. M. %A Kenny, D. J. %A Rohlhill, J. %A Knoblauch, J. %A Knoblauch, M. %A Lohaus, G. %A Tappero, R. %A Scherzer, S. %A Hedrich, R. %A Jensen, K. H. %D 2022 %J Nature Plants %K energy-source mobile myOwn %N 2 %P 171-+ %R 10.1038/s41477-022-01098-x %T Sugar loading is not required for phloem sap flow in maize plants %U /brokenurl#<Go to ISI>://WOS:000759690700015 %V 8 %X Phloem transport of photoassimilates from leaves to non-photosynthetic organs, such as the root and shoot apices and reproductive organs, is crucial to plant growth and yield. For nearly 90 years, evidence has been generally consistent with the theory of a pressure-flow mechanism of phloem transport. Central to this hypothesis is the loading of osmolytes, principally sugars, into the phloem to generate the osmotic pressure that propels bulk flow. Here we used genetic and light manipulations to test whether sugar import into the phloem is required as the driving force for phloem sap flow. Using carbon-11 radiotracer, we show that a maize sucrose transporter1 (sut1) loss-of-function mutant has severely reduced export of carbon from photosynthetic leaves (only similar to 4% of the wild type level). Yet, the mutant remarkably maintains phloem pressure at similar to 100% and sap flow speeds at similar to 50-75% of those of wild type. Potassium (K+) abundance in the phloem was elevated in sut1 mutant leaves. Fluid dynamic modelling supports the conclusion that increased K+ loading compensated for decreased sucrose loading to maintain phloem pressure, and thereby maintained phloem transport via the pressure-flow mechanism. Furthermore, these results suggest that sap flow and transport of other phloem-mobile nutrients and signalling molecules could be regulated independently of sugar loading into the phloem, potentially influencing carbon-nutrient homoeostasis and the distribution of signalling molecules in plants encountering different environmental conditions.

@article{RN967, abstract = {Phloem transport of photoassimilates from leaves to non-photosynthetic organs, such as the root and shoot apices and reproductive organs, is crucial to plant growth and yield. For nearly 90 years, evidence has been generally consistent with the theory of a pressure-flow mechanism of phloem transport. Central to this hypothesis is the loading of osmolytes, principally sugars, into the phloem to generate the osmotic pressure that propels bulk flow. Here we used genetic and light manipulations to test whether sugar import into the phloem is required as the driving force for phloem sap flow. Using carbon-11 radiotracer, we show that a maize sucrose transporter1 (sut1) loss-of-function mutant has severely reduced export of carbon from photosynthetic leaves (only similar to 4% of the wild type level). Yet, the mutant remarkably maintains phloem pressure at similar to 100% and sap flow speeds at similar to 50-75% of those of wild type. Potassium (K+) abundance in the phloem was elevated in sut1 mutant leaves. Fluid dynamic modelling supports the conclusion that increased K+ loading compensated for decreased sucrose loading to maintain phloem pressure, and thereby maintained phloem transport via the pressure-flow mechanism. Furthermore, these results suggest that sap flow and transport of other phloem-mobile nutrients and signalling molecules could be regulated independently of sugar loading into the phloem, potentially influencing carbon-nutrient homoeostasis and the distribution of signalling molecules in plants encountering different environmental conditions.}, added-at = {2024-02-14T14:38:32.000+0100}, author = {Babst, B. A. and Braun, D. M. and Karve, A. A. and Baker, R. F. and Tran, T. M. and Kenny, D. J. and Rohlhill, J. and Knoblauch, J. and Knoblauch, M. and Lohaus, G. and Tappero, R. and Scherzer, S. and Hedrich, R. and Jensen, K. H.}, biburl = {https://www.bibsonomy.org/bibtex/2a74bbebfb097d4bb7370f18ea16abd70/rainerhedrich_2}, doi = {10.1038/s41477-022-01098-x}, interhash = {e8e460f7f893adf67edb6646eb567158}, intrahash = {a74bbebfb097d4bb7370f18ea16abd70}, issn = {2055-026x}, journal = {Nature Plants}, keywords = {energy-source mobile myOwn}, note = {Zf6qr Times Cited:16 Cited References Count:85}, number = 2, pages = {171-+}, timestamp = {2024-02-14T14:38:32.000+0100}, title = {Sugar loading is not required for phloem sap flow in maize plants}, type = {Journal Article}, url = {/brokenurl#<Go to ISI>://WOS:000759690700015}, volume = 8, year = 2022 }