Simultaneous efflux and uptake of metabolites by roots of wheat

Abstract

Background & aims Some metabolites (e.g. amino acids) present in root exudates can be taken up by roots, but we do not know if this ability extends to the broader suite of metabolites found in exudates. The aim of this study was to examine the ability of wheat (Triticum aestivum L.) to efflux and take up a broad suite of small metabolites. Methods Four-week-old plants were placed into an uptake solution that contained a broad suite of 13 C-labelled metabolites. Uptake was estimated from the decrease in concentration of the 13 C isotopologue in the solution; and from the appearance of 13 C isotopologues within roots. Efflux was estimated from appearance of 12 C isotopologues in solution.Results When wheat plants were placed in 13 C-metabolite solutions the concentration of U-13 C isotopologues of 37 metabolites decreased -as would be expected if plants were taking up the U-13 C metabolites. After 4 h immersion in 13 C metabolite solution, roots contained detectable amounts of U-13 C isotopologues of 55 metabolites. U-13 C isotopologues of organic acids were not detected within roots.Conclusions These findings indicate that wheat can take up a broad suite of N-containing metabolites and some sugars, but there was no evidence for uptake of organic acids.

Phosphorus deficiency changes carbon isotope fractionation and triggers exudate reacquisition in tomato plants

“…In this respect, it is interesting to note that a monosaccharide transporter superfamily has been already identified in plants therefore supporting the hypothesis of a root uptake process of monosaccharides 49 . This idea is further supported by the findings obtained by using 13 C isotopologues in wheat 28 . Furthermore, this possibility has been also confirmed in two other older studies conducted using maize as a model plant 30 , 40 .…”

“…Thus, root exudation could represent a great energy loss exacerbating the trade-offs between investments and returns in terms of nutrients. The exudates' reacquisition by roots is potentially possible, even though only limited information is available 16,17,28,30,40 . In this work it has been postulated that plants can recapture some of the released C also triggering some specific exudate uptake mechanisms, as for instance in nutrient deficient conditions 16 .…”

“…Therefore, a further use of these compounds by the plant could represent an element of a more complex energy-saving strategy adopted by the plants. In fact, it has been demonstrated that some plants have the ability to recapture exudates from the apoplast or directly from the soil solution 16,28 . This phenomenon has been described for amino acids, sugars, polyamines and phytosiderophores, being these latter key players in iron (Fe) uptake in grasses species 16,28,29 .…”

“…However, to date no root uptake has been documented for organic acids. It has been hypothesized that the transmembrane electrochemical gradient prevents their transport towards the cytoplasm 28 . Considering the mechanism, the root uptake of amino acids, sugars, polyamines and phytosiderophores has been described as an active transport catalyzed by specific transporters and based on the transmembrane cotransport 28,30 .…”

“…It has been hypothesized that the transmembrane electrochemical gradient prevents their transport towards the cytoplasm 28 . Considering the mechanism, the root uptake of amino acids, sugars, polyamines and phytosiderophores has been described as an active transport catalyzed by specific transporters and based on the transmembrane cotransport 28,30 . It has been postulated that the root uptake of exudates could be a strategy for the plant to use C, sulfur (S) or N from organic matter 31 .…”