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Revisiting yield in terms of phloem transport to grains suggests phloem sap movement might be homeostatic in wheat
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  • Guillaume Tcherkez,
  • Meisha Holloway-Phillips,
  • Jeremy Lothier,
  • Anis Limami,
  • Marilyn Ball
Guillaume Tcherkez
Australian National University Research School of Biology

Corresponding Author:[email protected]

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Meisha Holloway-Phillips
Universitat Basel Departement Umweltwissenschaften
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Jeremy Lothier
Institut de Recherche en Horticulture et Semences
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Anis Limami
Institut de Recherche en Horticulture et Semences
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Marilyn Ball
Australian National University Research School of Biology
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Phloem sap transport, velocity and allocation have been proposed to play a role in physiological limitations of crop yield, along with photosynthetic activity or water use efficiency. Although there is clear evidence that carbon allocation to grains effectively drives yield in cereals like wheat (as reflected by the harvest index), the influence of phloem transport rate and velocity is less clear. Here, we took advantage of previously published data on yield, respiration, carbon isotope composition, nitrogen content and water consumption in winter wheat cultivars grown across several sites with or without irrigation, to express grain production in terms of phloem sucrose transport and compare with xylem water transport. Our results suggest that phloem sucrose transport rate follows the same relationship with phloem N transport regardless of irrigation conditions and cultivars, and seems to depend mostly on grain weight (i.e. mg per grain). When compared to xylem sap water movement, phloem sap velocity (in m s -1) was 5.8 to 7.7 times lower. Depending on the assumption made for phloem sap sucrose concentration, either phloem sap velocity or its proportionality coefficient to xylem velocity change little with environmental conditions. Taken as a whole, phloem transport from leaves to grains seems to be homeostatic within a narrow range of values and following relationships with other plant physiological parameters across cultivars and conditions. This suggests that phloem transport per se is not a limitation for yield in wheat but rather, is controlled to sustain grain filling.
06 Apr 2023Submitted to Plant, Cell & Environment
10 Apr 2023Submission Checks Completed
10 Apr 2023Assigned to Editor
10 Apr 2023Review(s) Completed, Editorial Evaluation Pending
18 Apr 2023Reviewer(s) Assigned
26 May 2023Editorial Decision: Revise Minor
27 May 20231st Revision Received
31 May 2023Submission Checks Completed
31 May 2023Assigned to Editor
03 Jun 2023Review(s) Completed, Editorial Evaluation Pending
05 Jun 2023Editorial Decision: Accept