Marco M Lehmann1, Melanie Egli2, Nadine Brinkmann2, Roland A Werner3, Matthias Saurer1, Ansgar Kahmen2. 1. Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf, Switzerland. 2. Department of Environmental Sciences - Botany, University of Basel, Basel, Switzerland. 3. Institute of Agricultural Sciences, ETH Zurich, Zurich, Switzerland.
Abstract
RATIONALE: The oxygen isotopic composition (here shown as the δ18 O value) of soluble sugars in leaves and phloem tissue holds valuable information about plant functions in response to climatic changes. However, δ18 O analysis of sugars is prone to error, and thoroughly tested methods are lacking. METHODS: We performed three experiments to test if sample preparation modifies the δ18 O values of sugars. In experiment 1, we tested the effects of oven-drying versus freeze-drying, whereas in experiment 2 we focused on the extraction and purification of leaf sugars. In experiment 3, we investigated the exudation and purification of twig phloem sugars as a function of exudation time and different ethylenediaminetetraacetic acid (EDTA) exudation media. RESULTS: Freeze-drying produced more consistent δ18 O values than oven-drying for sucrose but not for phloem sugars. The extraction and purification of leaf sugars can be performed without a significant modification of their δ18 O values; yet the purified leaf and phloem sugars possessed higher δ18 O values than the fraction of water-soluble compounds. Moreover, the exudation time significantly modulated the δ18 O values of phloem sugars, which is probably related to changes in the sugar composition. The addition of EDTA did not improve the determination of the δ18 O values of phloem sugars. CONCLUSIONS: We show that the sample preparation of plant sugars for the reliable determination of δ18 O values requires a strict protocol, which is described in this paper. For phloem sugar, we recommend a maximum exudation time of 1 h to reduce the degradation of sucrose and minimise oxygen isotope exchange reactions between the resulting hexoses and water.
RATIONALE: The oxygen isotopic composition (here shown as the δ18 O value) of soluble sugars in leaves and phloem tissue holds valuable information about plant functions in response to climatic changes. However, δ18 O analysis of sugars is prone to error, and thoroughly tested methods are lacking. METHODS: We performed three experiments to test if sample preparation modifies the δ18 O values of sugars. In experiment 1, we tested the effects of oven-drying versus freeze-drying, whereas in experiment 2 we focused on the extraction and purification of leaf sugars. In experiment 3, we investigated the exudation and purification of twig phloem sugars as a function of exudation time and different ethylenediaminetetraacetic acid (EDTA) exudation media. RESULTS: Freeze-drying produced more consistent δ18 O values than oven-drying for sucrose but not for phloem sugars. The extraction and purification of leaf sugars can be performed without a significant modification of their δ18 O values; yet the purified leaf and phloem sugars possessed higher δ18 O values than the fraction of water-soluble compounds. Moreover, the exudation time significantly modulated the δ18 O values of phloem sugars, which is probably related to changes in the sugar composition. The addition of EDTA did not improve the determination of the δ18 O values of phloem sugars. CONCLUSIONS: We show that the sample preparation of plant sugars for the reliable determination of δ18 O values requires a strict protocol, which is described in this paper. For phloem sugar, we recommend a maximum exudation time of 1 h to reduce the degradation of sucrose and minimise oxygen isotope exchange reactions between the resulting hexoses and water.
Authors: Philipp Schuler; Marc-André Cormier; Roland A Werner; Nina Buchmann; Arthur Gessler; Valentina Vitali; Matthias Saurer; Marco M Lehmann Journal: Plant Cell Environ Date: 2021-09-30 Impact factor: 7.947