Functional Group Properties and Position Drive Differences in Xenobiotic Plant Uptake Rates, but Metabolism Shares a Similar Pathway.

Plant uptake of xenobiotic compounds is crucial for phytoremediation (including green stormwater infrastructure) and exposure potential during crop irrigation with recycled water. Experimentally determining the plant uptake for every relevant chemical is impractical; therefore, illuminating the role of specific functional groups on the uptake of trace organic contaminants is needed to enhance predictive power. We used benzimidazole derivatives to probe the impact of functional group electrostatic properties and position on plant uptake and metabolism using the hydroponic model plant Arabidopsis thaliana. The greatest plant uptake rates occurred with an electron-withdrawing functional group at the 2 position; however, uptake was still observed with an electron-donating group. An electron-donating group at the 1 position significantly slowed uptake for both benzimidazole- and benzotriazole-based molecules used in this study, indicating possible steric effects. For unsubstituted benzimidazole and benzotriazole structures, the additional heterocyclic nitrogen in benzotriazole increased plant uptake rates compared to benzimidazole. Analysis of quantitative structure-activity relationship parameters for the studied compounds implicates energy-related molecular descriptors as uptake drivers. Despite significantly varied uptake rates, compounds with different functional groups yielded shared metabolites, including an impact on endogenous glutathione production. Although the topic is complex and influenced by multiple factors in the field, this study provides insights into the impact of functional groups on plant uptake, with implications for environmental fate and consumer exposure.

Rapid plant uptake of isothiazolinone biocides and formation of metabolites by hydroponic Arabidopsis.

Isothiazolinones biocides are water-soluble, low molecular weight, nitrogenous compounds widely used to prevent microbial growth in a variety of applications including personal care products and building façade materials. Because isothiazolinones from buildings wash off and enter stormwater, interactions with terrestrial plants may represent an important part of the environmental fate of these compounds (e.g., in green stormwater infrastructure). Using the model plant Arabidopsis thaliana grown hydroponically, we observed rapid (≥99% within 24 hours), plant-driven removal of four commonly used isothiazolinones: benzisothiazolinone (BIT), chloromethylisothiazolinone, methylisothiazolinone, and octylisothiazolinone. No significant differences in uptake rate occurred between the four compounds; therefore, BIT was used for further detailed investigation. BIT uptake by Arabidopsis was concentration-dependent in a manner that implicates transporter-mediated substrate inhibition. BIT uptake was also minimally impacted by multiple BIT spikes, suggesting constituently active uptake. BIT plant uptake rate was robust, unaffected by multiple inhibitors. We investigated plant metabolism as a relevant removal process. Proposed major metabolites that significantly increased in the BIT-exposure treatment compared to the control included: endogenous plant compounds nicotinic acid (confirmed with a reference standard) and phenylthioacetohydroximic acid, a possible amino acid-BIT conjugate, and two accurate masses of interest. Two of the compounds (phenylthioacetohydroximic acid and TP 470) were also present in increased amounts in the hydroponic medium after BIT exposure, possibly via plant excretion. Upregulation of endogenous plant compounds is environmentally significant because it demonstrates that BIT impacts plant biology. The rapid plant-driven isothiazolinone removal observed here indicates that plant-isothiazolinone processes could be relevant to the environmental fate of these stormwater compounds.

Impact of vegetation selection on nitrogen and phosphorus processing in bioretention containers.

A year-long bioretention container study in Maryland, USA, measured the relationship between three plant species (Eutrochium dubium, Iris versicolor, and Juncus effusus) and N ( NO 3 - , NO 2 - , NH 4 + , total nitrogen [TN], total dissolved nitrogen [TDN], dissolved organic nitrogen, particulate organic nitrogen [PON]) and total phosphorus (TP) removal from synthetic stormwater. Statistically significant removal was only found for NO 3 - and TP. Plant-independent NO 3 - removal occurred 9 months after planting, and then changed to removal only by the least-densely planted Juncus treatment. Removal in higher-density Juncus plantings was suspected to be limited by preferential pathways created by high root density. Juncus' low-density NO 3 - removal success correlates with its high growth rate, root mass and length, and large biomass, matching previous literature. TP removal was plant-independent. Shoot harvesting of one plant of each species after 1 year would remove 0.61 g N. Of the plant species in this study, Juncus effusus is most highly recommended for bioretention for its nutrient removal dynamics and year-round green aesthetics. PRACTITIONER POINTS: Only the one-Juncus density treatment had significant NO 3 - removal. All Juncus treatments as well as non-Juncus treatments prevented the PON, TN, or TDN export seen in the No-plants control. TP removal was plant-independent. Juncus had the greatest biomass increase and biomass N. Shoots contain the majority of biomass N for each plant species. Juncus and Iris had high survivorship. Joe Pye had low survivorship. These, and all other study results, need field-scale verification.

Cdc42 GTPase and Rac1 GTPase act downstream of p120 catenin and require GTP exchange during gastrulation of zebrafish mesoderm.

BACKGROUND: We investigated the roles of p120 catenin, Cdc42, Rac1, and RhoA GTPases in regulating migration of presomitic mesoderm cells in zebrafish embryos. p120 catenin has dual roles: It binds the intracellular and juxtamembrane region of cadherins to stabilize cadherin-mediated adhesion with the aid of RhoA GTPase, and it activates Cdc42 GTPase and Rac1 GTPase in the cytosol to initiate cell motility. RESULTS: During gastrulation of zebrafish embryos, knockdown of the synthesis of zygotic p120 catenin δ1 mRNAs with a splice-site morpholino caused lateral widening and anterior-posterior shortening of the presomitic mesoderm and somites and a shortened anterior-posterior axis. These phenotypes indicate a cell-migration effect. Co-injection of low amounts of wild-type Cdc42 or wild-type Rac1 or dominant-negative RhoA mRNAs, but not constitutively-active Cdc42 mRNA, rescued these p120 catenin δ1-depleted embryos. CONCLUSIONS: These downstream small GTPases require appropriate spatiotemporal stimulation or cycling of GTP to guide mesodermal cell migration. A delicate balance of Rho GTPases and p120 catenin underlies normal development.