Omeprazole Enhances Mechanical Stress-Induced Root Growth Reduction in Arabidopsis thaliana

The root growth reduction in response to mechanical stress involves ethylene-mediated microtubule reorganization and transmembrane receptor-mediated signal transduction in Arabidopsis

We found that mutations in a Ca²⁺-permeable mechanosensitive channel MCA1, an ethylene-regulated microtubule-associated protein WDL5, and a versatile co-receptor BAK1 affect root growth response to mechanical stress. Plant root tips exposed to mechanical impedance show a temporal reduction in the elongation growth. The process involves a transient Ca²⁺ increase in the cytoplasm followed by ethylene signaling. To dissect the molecular mechanisms underlying this response, we examined the root growth of a series of Arabidopsis mutants with potentially altered response to mechanical stress after transfer from vertical to horizontal plates that were covered by dialysis membrane as an impedance. Among the plant hormone-response mutants tested, the ethylene-insensitive mutant ein3 was confirmed to show no growth reduction after the transfer. The root growth reduction was attenuated in a mutant of MCA1 encoding a Ca²⁺-permeable mechanosensitive channel and that of WDL5 encoding an ethylene-regulated microtubule-associated protein. We also found that the growth reduction was enhanced in a mutant of BAK1 encoding a co-receptor that pairs with numerous leucine-rich repeat receptor kinases to modulate growth and immunity. These results suggest the root growth reduction in response to mechanical stress involves ethylene-mediated microtubule reorganization and also transmembrane receptor-mediated signal transduction.

Sustainable Cropping Requires Adaptation to a Heterogeneous Rhizosphere

Root-soil interactions in the rhizosphere are central to resource acquisition and crop production in agricultural systems. However, apart from studies in idealized experimental systems, rhizosphere processes in real agricultural soils in situ are largely uncharacterized. This limits the contribution of rhizosphere science to agriculture and the ongoing Green Revolution. Here, we argue that understanding plant responses to soil heterogeneity is key to understanding rhizosphere processes. We highlight rhizosphere sensing and root-induced soil modification in the context of heterogeneous soil structure, resource distribution, and root-soil interactions. A deeper understanding of the integrated and dynamic root-soil interactions in the heterogeneously structured rhizosphere could increase crop production and resource use efficiency towards sustainable agriculture.

Phosphate Deprivation Can Impair Mechano-Stimulated Cytosolic Free Calcium Elevation in Arabidopsis Roots

The root tip responds to mechanical stimulation with a transient increase in cytosolic free calcium as a possible second messenger. Although the root tip will grow through a heterogeneous soil nutrient supply, little is known of the consequence of nutrient deprivation for such signalling. Here, the effect of inorganic phosphate deprivation on the root’s mechano-stimulated cytosolic free calcium increase is investigated. Arabidopsisthaliana (cytosolically expressing aequorin as a bioluminescent free calcium reporter) is grown in zero or full phosphate conditions, then roots or root tips are mechanically stimulated. Plants also are grown vertically on a solid medium so their root skewing angle (deviation from vertical) can be determined as an output of mechanical stimulation. Phosphate starvation results in significantly impaired cytosolic free calcium elevation in both root tips and whole excised roots. Phosphate-starved roots sustain a significantly lower root skewing angle than phosphate-replete roots. These results suggest that phosphate starvation causes a dampening of the root mechano-signalling system that could have consequences for growth in hardened, compacted soils.

Omeprazole Treatment Enhances Nitrogen Use Efficiency Through Increased Nitrogen Uptake and Assimilation in Corn

Omeprazole is a selective proton pump inhibitor in humans that inhibits the H+/K+-ATPase of gastric parietal cells. Omeprazole has been recently shown to act as a plant growth regulator and enhancer of salt stress tolerance. Here, we report that omeprazole treatment in hydroponically grown maize improves nitrogen uptake and assimilation. The presence of micromolar concentrations of omeprazole in the nutrient solution alleviates the chlorosis and growth inhibition induced by low nitrogen availability. Nitrate uptake and assimilation is enhanced in omeprazole treated plants through changes in nitrate reductase activity, primary metabolism, and gene expression. Omeprazole enhances nitrate assimilation through an interaction with nitrate reductase, altering its activation state and affinity for nitrate as a substrate. Omeprazole and its targets represent a novel method for enhancing nitrogen use efficiency in plants.

Omeprazole Promotes Chloride Exclusion and Induces Salt Tolerance in Greenhouse Basil

The role of small bioactive molecules (<500 Da) in mechanisms improving resource use efficiency in plants under stress conditions draws increasing interest. One such molecule is omeprazole (OMP), a benzimidazole derivative and inhibitor of animal proton pumps shown to improve nitrate uptake and exclusion of toxic ions, especially of chloride from the cytosol of salt-stressed leaves. Currently, OMP was applied as substrate drench at two rates (0 or 10 μM) on hydroponic basil (Ocimum basilicum L. cv. Genovese) grown under decreasing NO3−:Cl− ratio (80:20, 60:40, 40:60, or 20:80). Chloride concentration and stomatal resistance increased while transpiration, net CO2 assimilation rate and beneficial ions (NO3−, PO43−, and SO42−) decreased with reduced NO3−:Cl− ratio under the 0 μM OMP treatment. The negative effects of chloride were not only mitigated by the 10 μM OMP application in all treatments, with the exception of 20:80 NO3−:Cl−, but plant growth at 80:20, 60:40, and 40:60 NO3−:Cl− ratios receiving OMP application showed maximum fresh yield (+13%, 24%, and 22%, respectively), shoot (+10%, 25%, and 21%, respectively) and root (+32%, 76%, and 75%, respectively) biomass compared to the corresponding untreated treatments. OMP was not directly involved in ion homeostasis and compartmentalization of vacuolar or apoplastic chloride. However, it was active in limiting chloride loading into the shoot, as manifested by the lower chloride concentration in the 80:20, 60:40, and 40:60 NO3−:Cl− treatments compared to the respective controls (−41%, −37%, and −24%), favoring instead that of nitrate and potassium while also boosting photosynthetic activity. Despite its unequivocally beneficial effect on plants, the large-scale application of OMP is currently limited by the molecule’s high cost. However, further studies are warranted to unravel the molecular mechanisms of OMP-induced reduction of chloride loading to shoot and improved salt tolerance.