The role of proline and betaine functionalized zinc oxide nanoparticles as drought stress regulators in Coriandrum sativum: an in vivo study

Drought stress poses a significant environmental challenge that substantially hinders plant growth and agricultural productivity on a global scale. This stress disrupts water uptake, moderates photosynthetic efficiency, and induces oxidative stress in plants, resulting in considerable yield reductions. Recent advancements in nanotechnology present promising approaches to enhance plant resilience against abiotic stresses. To study the influence of drought stress on vegetative growth of coriander plants and its mitigation by zinc oxide nanoparticles (ZnO NPs) coupled with proline (ZnO-P) and betaine (ZnO-B), a pot experiment was designed. Plants were exposed to drought stress and treated with 50 mg/kg and 100 mg/kg ZnO NPs, ZnO-P, and ZnO-B NPs (ZnO nanocomposites). Plants were watered on wilting. It was observed that in control drought stress plants, the pots were irrigated 8–10 times while the watering requirement reduced for 5–6 time to the plants when fertilized with ZnO nanocomposites. Significant improvement in vegetative parameters (length and weight) was observed under ZnO nanocomposites treatment. At 50 mg/kg of ZnO-P NPs, shoot length increased up to 71% while root length increased up to 24%. Shoot and root fresh weight was improved (5 g and 1.5 g, respectively) at 50 mg/kg of ZnO-P NPs. The total phenolics and flavonoid contents that were increased in drought stress plants, significantly decreased both in roots and shoots of ZnO nanocomposites. Ttotal antioxidant and total reducing power responses also remarkably decreased in shoots of ZnO nanocomposites while in roots the variation was inconsistent. The free radical scavenging potential was also variable in both shoots and roots of coriander plants. Decrease in super oxide and per oxide dismutase activities (up to 33% and 32%, respectively) were observed when pots were added with ZnO nanocomposites. The findings demonstrate that drought stress can be reduced by applying proline and betaine doped ZnO nanoparticles as fertilizer that mitigate the drought condition, strengthen the plants against stress, and also reduces the watering time to the crops to save water. Future research could explore the molecular mechanisms underlying these effects and evaluate the efficacy of ZnO nanocomposites in other crop species and under field conditions to further validate their potential for widespread agricultural use.