COS 15-6
Tracking the ever-elusive molecular composition of plant root exudates using surface-modified polymeric probes
Metabolites released from litter leachates and root exudates help the plants to adapt to a wide range of habitats by facilitating resource foraging and by promoting plant-organismal interactions. The overall effect of the exudation is regulated not only by the exudation processes itself, but also by the chemical transformation that these exudates undergo in soil matrices. The biological functions of these plant inputs are tightly governed by their composition and molecular identity. Yet the molecular composition of the exudates and their transformation pathways in soil matrices has remained ever-elusive due to complex biotic and abiotic interactions. We developed polymeric probes through in-situ polymerization of poly(styrene-co-vinylbenzyl chloride-co-divinylbenzene) to elucidate the chemical environment of the soil to which the plant roots are exposed to. The probes were subjected to post-polymerization surface modifications to enhance the extraction and retention capacity of plant metabolites. The efficacy of these probes was tested in soil-systems and extracted compounds were analyzed using various gas/liquid chromatography tandem-mass-spectrometry platforms.
Results/Conclusions
The unmodified polystyrene-divinylbenzene probes exhibited lower sorption affinity for monophenolic and flavonoid compounds with the overall partitioning coefficient <1. Hypercrosslinking of the polymeric probes through an in-situ Friedel-Crafts alkylation significantly increased the surface area and the sorption capacity of the probes, resulting in >10 fold increase in the partitioning of the plant metabolites onto the probes. Scanning electron microscopy revealed extensive modification of the surface of the probes through hypercrosslinking, however the mechanical rigidity of the probes was affected during the hypercrosslinking. The probes exhibited a lower site specific sorption (slope of Freundlich adsorption isotherm close to unity) and percent recovery of the sorbed compounds from the probes were >70, indicating a predominance of reversible sorption. Polymeric probes coupled with mass spectrometry analysis enables us to capture and identify more than 50 metabolites (<1kDa) from the soil matrices in a forested ecosystem. The flavonoid glycosides exhibited significantly lower sorption affinity to the probes than their respective aglycones indicating a potential biasness of probes towards hydrophobic metabolites. Increasing the molecular specificity of the probes through template impregnation and surface grafting will be attempted.