Document Type
Article
Publication Date
7-22-2021
Publication Title
The New Phytologist
Abstract
A robust understanding of phloem functioning in tall trees evades us because current methods for collecting phloem sap do not lend themselves to measuring actively photosynthesizing canopy leaves. We show that Raman spectroscopy can be used as a quantitative tool to assess sucrose concentration in leaf samples. Specifically, we found that Raman spectroscopy can predict physiologically relevant sucrose concentrations (adjusted R2 of 0.9) in frozen leaf extract spiked with sucrose. We then apply this method to estimate sieve element sucrose concentration in rapidly frozen petioles of canopy red oak (Quercus rubra) trees and found that sucrose concentrations are > 1100 mM at midday and midnight. This concentration is predicted to generate a sieve element turgor pressure high enough to generate bulk flow through the phloem, but is potentially too high to allow for sucrose diffusion from photosynthetic cells. Our findings support the Münch hypothesis for phloem transport once the carbon is in the phloem and challenge the passive-loading hypothesis for carbon movement into the phloem for red oak. This study provides the first ˜in-situ (frozen in the functioning state) source sieve element sucrose concentration characterization in any plant, opening a new avenue for investigation of phloem functioning.
Volume
232
Issue
1
First Page
418
Last Page
424
DOI
doi.org/10.1111/nph.17465
Rights
© 2021 The Authors
Recommended Citation
Gersony, Jess T.; McClelland, Arthur; and Holbrook, N Michele, "Raman Spectroscopy Reveals High Phloem Sugar Content in Leaves of Canopy Red Oak Trees" (2021). Biological Sciences: Faculty Publications, Smith College, Northampton, MA.
https://scholarworks.smith.edu/bio_facpubs/292
Comments
Archived as published. Open access article.