Document Type : Research Paper

Authors

• Mohammad Haghaninia ¹
• abdollah javanmard ²
• Zahra Ghorbani ¹
• mohammad reza morshedloo ³
• Karim Kakaei ¹

¹ University of Maragheh

² university of maragheh

³ Maragheh Uinversity

Abstract

    Background and Objective: In contemporary times, the importance of medicinal plants and their identification in advancing national, regional, and global objectives, such as achieving health, pharmaceutical self-sufficiency, fostering employment, and promoting economic development, is indisputable. Mentha suaveolens × Mentha piperita, commonly referred to as grapefruit mint, is recognized as a valuable medicinal plant within the Lamiaceae family. Drought stands out as a major limiting factor for global plant growth, constituting the most prevalent environmental stressor that disrupts the balance between reactive oxygen species and antioxidant defense mechanisms, thereby inducing oxidative stress. Nanotechnology emerges as a modern approach with notable potential to enhance plant resilience against drought stress. Among various nanomaterials, carbon quantum dots, discovered in 2004, possess distinctive characteristics, including dimensions below 10 nanometers, reduced toxicity, and superior biocompatibility compared to metal-based alternatives, owing to their carbonaceous structure. Due to these unique attributes, carbon quantum dots have attracted significant research interest in recent years. Therefore, this study aimed to evaluate the effects of carbon quantum dots on the growth, yield, and essential oil composition of grapefruit mint (Mentha suaveolens × piperita) under drought stress conditions.
Methodology: This research was conducted as a factorial experiment in a completely randomized design with four replications in pots during the spring and summer of 2023 at the research greenhouse of Maragheh University, East Azerbaijan, Iran. The first factor was irrigation at 90% of field capacity (FC) as control (normal irrigation), irrigation at 70% FC (moderate stress), and irrigation at 50% FC (severe stress). The second factor consisted of different levels of carbon quantum dots (0, 5, 10, 15, and 20 parts per million). Data collected from sampling were analyzed using SAS statistical software, and means were compared using the least significant difference (LSD) test at the 5% level.
Results: Analysis of variance indicated that the effects of different irrigation regimes, fertilizer treatments, and their interaction on all measured traits were significant. The findings revealed that the application of 15 ppm carbon quantum dots under normal irrigation increased fresh weight, dry weight, chlorophyll a, and chlorophyll b contents by 110%, 86%, 184%, and 163%, respectively, compared to no CQD application under severe drought stress. Under moderate stress, the use of 15 ppm carbon quantum dots increased essential oil content by 135% and essential oil yield by 298% compared to severe stress without CQD. Furthermore, the highest linalyl acetate content was obtained with 15 ppm carbon quantum dots under 50% FC, showing a 50.1% increase compared to the control treatment. Similarly, the highest linalool content was recorded under normal irrigation with 10 ppm carbon quantum dots, representing a 67.4% increase compared to no CQD application under 50% FC. Moreover, under normal irrigation, 15 ppm carbon quantum dots reduced malondialdehyde and hydrogen peroxide contents by 51% and 58%, respectively, compared to no CQD application under severe stress. Additionally, under mild stress, 15 ppm carbon quantum dots enhanced the activity of superoxide dismutase, guaiacol peroxidase, and ascorbate peroxidase enzymes by 123%, 111%, and 72%, respectively, compared to no fertilizer application under normal conditions.
Conclusion: The results indicate that applying 15 ppm carbon quantum dots can promote growth by modulating secondary metabolites and strengthening defense mechanisms through the activation of antioxidant enzymes and increasing the accumulation of osmolytes such as proline and total soluble sugars, thereby reducing malondialdehyde and hydrogen peroxide levels. This enhancement in grapefruit mint plants contributes to improved drought resilience, ultimately enhancing both the quantity and quality of the essential oil.

Keywords

• antioxidant enzymes
• drought stress
• secondary metabolite
• essential oil yield
• nanoparticles
• sustainable agriculture

Main Subjects

• Agriculture and horticulture