AI Article Synopsis

  • Phloem transport is essential for moving sugar from leaves to parts of the plant that don't photosynthesize, which supports growth and yield.
  • Researchers tested the role of sugar loading in phloem transport using a mutant maize variety lacking a specific sucrose transporter, finding that it could still maintain phloem pressure and sap flow despite reduced sugar export.
  • The study suggests that potassium levels in the phloem helped compensate for lower sugar levels, indicating that nutrient and signaling transport in plants might be managed separately from sugar loading, which could impact how plants respond to environmental changes.

Article 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 ~4% of the wild type level). Yet, the mutant remarkably maintains phloem pressure at ~100% and sap flow speeds at ~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.

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Source
http://dx.doi.org/10.1038/s41477-022-01098-xDOI Listing

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