The spatial variability of the nitrate (NO₃^‐) uptake along the maize primary root axis was investigated at physiological and molecular levels. Net NO₃^‐ uptake rate (NNUR) and its kinetic parameters, together with the gene expression of a high‐affinity NO₃^‐ transporter (NRT2.1), were evaluated. The activity and the expression of plasma membrane H⁺‐ATPase (PM H⁺‐ATPase), key enzyme in plant nutrition, were also analysed. The NNUR showed a heterogeneous spatial pattern along the root, where the regions closer to the root tip early exhibited higher capacity to absorb NO₃^‐ than the basal regions, because of a higher maximum NNUR and faster induction of the inducible high‐affinity transport system (iHATS), the presence of the high‐affinity transport system (HATS) also at external NO₃^‐ concentrations >100 µm and an improved NO₃^‐ transport because of lower K_m values. ZmNRT2.1 transcript abundances were not spatially correlated with NNUR, suggesting that post‐translational effects or NAR2 protein co‐expression could be involved. By contrast, PM H⁺‐ATPase displayed a similar spatial–temporal pattern as that of nitrate uptake, resulting in higher activity in the root tip than in the basal regions. Increased activities of the enzyme after nitrate supply resulted in enhanced expression of MAH3 and MAH4, PM H⁺‐ATPase subfamily II genes, while MAH1 was not expressed.

Coumarin is a natural compound well known for its phytotoxic potential. In the search for new herbicidal compounds to manage weeds, three synthetic derivatives bearing the coumarin scaffold (1–3), synthesized by a carbonylative organometallic approach, were in vitro assayed on germination and root growth of two noxious weeds, Amaranthus retroflexus and Echinochloa crus-galli. Moreover, the synthetic coumarins 1–3 were also in vitro assayed on seedlings growth of the model species Arabidopsis thaliana to identify the possible physiological targets. All molecules strongly affected seed germination and root growth of both weeds. Interestingly, the effects of synthetic coumarins on weed germination were higher than template natural coumarin, pointing out ED₅₀ values ranging from 50–115 µM. Moreover, all synthetic coumarins showed a strong phytotoxic potential on both Arabidopsis shoot and root growth, causing a strong reduction in shoot fresh weight (ED₅₀ values ≤ 60 µM), accompanied by leaf development and a decrease in pigment content. Furthermore, they caused a strong alteration in root growth (ED₅₀ values ≤ 170 µM) and morphology with evident alterations in root tip anatomy. Taken together, our results highlight the promising potential herbicidal activity of these compounds.

Seven-day-old maize seedlings grown in a nitrogen-free hydroponic culture were exposed for 48 h to 0, 100 and 300 μM trans-cinnamic, p-coumaric, ferulic, caffeic acids, umbelliferone and 200 μM KNO₃. Net nitrate uptake was affected by trans-cinnamic, ferulic and p-coumaric acids in a concentration-dependent manner, and trans-cinnamic acid appeared to be the strongest inhibitor. Conversely, at low concentrations, caffeic acid stimulated net nitrate uptake while umbelliferone did not influence it. After 24 h of treatment, plasma membrane H⁺-ATPase activity significantly decreased in a concentration-dependent manner in response to trans-cinnamic, ferulic and p-coumaric acids, while umbelliferone and caffeic acid had no effect on H⁺-ATPase activity.