Green Synthesized Zinc Oxide Nanoparticles Confer Drought Tolerance in Melon (Cucumis melo L.) (2023)


Plants face a myriad of environmental obstacles as they grow and develop, both in natural and cultivated environments. Drought, among other challenges, is indisputably one of the most urgent factors that can significantly affect plant productivity. Water is a vital element that contributes to many physiochemical processes in plants, such as growth, development, and metabolism. This is because 75-95% of a plant's fresh biomass is comprised of water, underscoring the importance of plant productivity (Brodersen et al., 2019). Therefore, drought is regarded as a primary environmental stressor for various plants (Diatta et al., 2020), especially in arid regions, and is regarded as the foremost significant global threat to food security, having triggered major famines in the past (Okorie et al., 2019). The effects of drought on farming are exacerbated by the exhaustion of water resources and the increasing demand for food, fueled by the alarming growth of the global population (O’Connell, 2017). The variability of drought occurrence is influenced by multiple factors, such as inconsistent and erratic precipitation patterns, evapotranspiration rates, and the water retention capacity of the rhizosphere (DeVincentis, 2020). In certain instances, plants may experience physiological drought, also referred to as pseudo-drought (Salehi-Lisar and Bakhshayeshan-Agdam, 2020), wherein they are incapable of taking in water from the soil, despite the presence of adequate moistness (Daryanto et al., 2017). In addition, drought stress exposure has a negative impact on various morpho-physiological, biochemical, and molecular characteristics, as well as the ecological processes of plants (Ortiz et al., 2015). Furthermore, water-deficient conditions negatively impact plant yield and quality (Battaglia et al., 2018). The way in which plants respond to drought is correlated with numerous aspects including plant species, growth stages, age, as well as the duration and severity of the drought (Gray and Brady, 2016). The mechanisms through which plants adapt to drought conditions vary among species. Consequently, plants can adapt their resource allocation and alter their growth behavior to effectively respond to the challenging environmental conditions caused by drought (Bielach et al., 2017). Numerous molecular networks, such as those associated with signal transduction, play an important role in enhancing the capability of crops to respond to drought stress (Zandalinas et al., 2020). According to a study, the application of ZnO.NPs increased the expression of Fe/Mn-SOD, Cu/Zn SOD, APX, CAT, WRKY, ERD and DREB genes in plants, resulting in improved tolerance against drought stress (Huang et al., 2012, Kandhol et al., 2022, Sun et al., 2020). Apart from molecular aspects underlying plant reaction to drought stress, plants also utilize stomatal regulation via augmented ion transportation, root acclimation, osmotic adjustments, and regulation of antioxidant enzymes (Kumar et al., 2019, Prakash et al., 2019).

As environmental challenges continue to escalate, melon (Cucumis melo L.) crops are becoming increasingly vulnerable to drought stress, highlighting the urgent need for innovative and sustainable approaches, such as the integration of nanoparticle technology. At present, the use of agrochemicals in agriculture is estimated to be 0.04 billion tons. However, this is projected to double by 2050 to support the food requirements of 9.5 billion individuals (Kah et al., 2019). It is crucial to adopt techniques that enable more efficient use of natural resources to achieve agricultural sustainability. In recent times, the utilization of nanotechnology has been on the rise in diverse fields, including agriculture. Nanoparticles (NPs) have the potential to serve as sources of micronutrients, providing plants with nutritional benefits and enhancing their tolerance against different types of stress (Raliya et al., 2015). Green synthesis is a relatively new area of nanobiotechnology that involves synthesizing nanoparticles using plant-based materials. Green synthesis is a simpler, cheaper, and more reproducible process that results in stable nanoparticles with minimal toxicity compared to other methods (Azmat et al., 2022). NPs have demonstrated the capacity to enhance plant growth when used at appropriate concentrations, in addition to their well-established role in biomedical applications (Khan et al., 2019). Zinc oxide nanoparticles (ZnO.NPs) have been found to play a significant role in enhancing plant growth and productivity, although higher concentrations can be toxic to plants (Zulfiqar et al., 2019). The incorporation of ZnO.NPs in plant growth and productivity can be attributed to the provision of essential zinc nutrients, which help adjust plant response mechanisms including, photosynthetic pigments production, cell elongation, expression of genes, and the upregulation of antioxidant enzymes (Yuvaraj and Subramanian, 2020). Number of researches have corroborated the constructive influence of ZnO.NPs on plant development, especially in unfavorable environmental conditions including drought. The incorporation of ZnO.NPs have been found to augment the antioxidant activity and relative water content in rice and soybean species, resulting in increased tolerance to drought stress conditions (Sedghi et al., 2013, Upadhyaya et al., 2020). There is limited understanding of the potential of ZnO.NPs synthesized from Artemisia annua bio-extract in mitigating drought stress, despite the positive influence of different metallic NPs on plant growth under various biotic and abiotic stresses. Therefore, the present research aims to investigate the potential use of green synthesized ZnO.NPs in enhancing C. melo crop response to drought stress, including stimulation of antioxidant enzymes activity and drought related marker genes, as well as the uptake of essential nutrients and photosynthetic functions.

Section snippets

Chemical materials

Fresh leaves of Artemisia annua and zinc sulphate heptahydrate (ZnSO4·7H2O) were acquired from the School of Agriculture and Biology, Shanghai Jiao Tong University, China. A. annua, commonly known as sweet wormwood, is a plant with significant medicinal properties, including, antibacterial, anti-inflammatory and antioxidant properties (Gomathi and Suhana, 2021, Wang et al., 2020a). Plant leaves were thoroughly cleaned with de-ionized water and kept to dry at ambient temperature. Desiccated

ZnO.NPs alleviate morphological alterations

The morphological parameters of melon seedlings were significantly affected by drought stress in DS treatment in comparison with the control (Table 2). The shoot length (SL), stem diameter (SD), leaf area (LA), Fv/Fm, shoot fresh and dry weight declined by approximately 23, 13, 14, 33, 77 and 45%, respectively, relative to the control. However, the treatment of ZnO.NPs significantly mitigated the deleterious impact of drought stress on shoot morphological attributes. Nonetheless, this effect


Plants encounter various abiotic stresses, but drought stress stands out as one of the most detrimental environmental challenges, obstructing numerous physiological and biochemical aspects, crucial for plant growth and productivity (Ashraf, 2010). To cope with fluctuating environmental conditions including drought, plants have evolved to develop a diverse set of defense responses including ROS scavenging mechanism through stimulating antioxidant enzymes and drought associated genes, stomatal


The present research illustrated that ZnO.NPs treatment improved the drought tolerance capability of C. melo seedlings along with improvement in nutrients uptake and vegetative growth. ZnO.NPs dosage momentously stimulated the upregulation of antioxidant enzymatic activities and gene expression which in turn reduced the oxidative damage and protected the ultrastructural integrity of the chloroplast. Furthermore, ZnO.NPs supplementation marked a significant improvement in photosynthetic

CRediT authorship contribution statement

Asad Rehman: Conceptualization, Experimentation, Writing – original draft, Writing – review & editing. Jinyang Weng and Pengli Li: Methodology, Software, Writing – review & editing. Iftikhar Hussain Shah and Saeed ur Rahman: Conceptualization, Investigation, Writing – review & editing. Muhammad Khalid: Software, Writing – review & editing. Muhammad Aamir Manzoor: Visualization, Writing – review & editing. Liying Chang: Supervision, Software, Writing – review & editing. Qingliang Niu:

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.


This work was supported by Shanghai Melon and Watermelon Industry Technical System, China (2017-2021).

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What is green synthesis of ZnO nanoparticles using? ›

Zinc oxide (ZnO) nanoparticles (NPs) have been synthesized using Hibiscus subdariffa leaf extract. Temperature dependent synthesis and particle growth have been studied. Formation of NPs was confirmed by UV-visible (UV-VIS) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD).

What is the role of zinc oxide nanoparticles in mediating abiotic stress responses in plant? ›

ZnO NPs stimulate the formation of phytohormones, osmolytes, antioxidant enzymes, and metabolites in plants against abiotic stress, revealing the promising role of ZnO NPs in combating the stress. However, ZnO NPs must be used in plants appropriately to obtain the benefits.

How are zinc oxide nanoparticles made? ›

First, the reaction between zinc acetate dihydrate and DEG/TEG leads to esterification that forms (Zn-OH)2. Further dehydration of (Zn-OH)2 results into formation of ZnO nanoparticles.

What is the advantage of green synthesis of nanoparticles? ›

Green synthesis is more beneficial than traditional chemical synthesis because it costs less, decreases pollution, and improves environmental and human health safety.

What is the effect of zinc oxide nanoparticles on plant growth? ›

ZnO NPs promote onion growth and reduce the flowering period at 20 and 30 mg/L concentrations (Laware and Raskar, 2014). Burman et al. (2013) reported an improved growth in the chickpea with foliar application of Zn, whereas Prasad et al. (2012) reported increased root/shoot growth in peanut plant.

What is the effect of nanoparticles on drought stress in plants? ›

NPs exhibit alleviating effects against drought stress via induction of physiological and biochemical readjustments accompanied by modulation of gene expression involved in drought response/tolerance. NPs ameliorate drought-induced reduction in carbon assimilation via increasing the photosynthetic activity.

What is the role of nanoparticles in drought stress? ›

Nanoparticles (NPs) play a key role in enhancing drought stress (DS) tolerance in plants. NPs reduce MDA accumulation, maintain membrane stability, induce the expression of stress-related proteins, improve nutrient and water uptake, increase photosynthesis, and increase grain yield and harvest index.

What is the critical role of zinc in plants facing the drought stress? ›

Moreover, Zn interacts with plant hormones, increases the expression of stress proteins and stimulates the antioxidant enzymes for counteracting drought effects.

What are the disadvantages of zinc oxide nanoparticles? ›

However, ZnO has several disadvantages, such as the fast recombination of photogenerated electron-hole pairs, it is only active with UV light, and it suffers from photocorrosion [64]. To solve these limitations, ZnO has been combined with other materials such as metals, semiconductors, and nanocarbons.

What is the toxic effect of zinc oxide nanoparticles? ›

Inhalation and instillation of ZnO NPs result in lung inflammation and systemic toxicity. The solubility of ZnO NPs plays an important role in this inflammation.

What is the difference between zinc oxide and nano zinc oxide? ›

“Non-nano” and “nano” refer to the size of the particles of zinc oxide. The range for "non-nano" is 100 nanometers (nm) or greater, while "nano" zinc oxide (used because it is non-whitening) is typically 10-20 nm in size. To give you a sense of how small that is, one nanometer is a billionth of a meter.

What is green synthesis method for nanoparticles? ›

Green synthesis employs a clean, safe, cost effective and environmentally friendly process of constructing nanomaterials. Microorganisms such as bacteria, yeast, fungi, algal species and certain plants act as substrates for the green synthesis of nanomaterials (Figure 3).

What is green chemical approach for nanoparticles? ›

Typically, the green synthesis of nanoparticles has been reported to involve mixing of preferably aqueous extracts with aqueous solution of metal salt. The reduction reaction completes in few minutes to few hours at room temperature.

What is green synthesis of nanoparticles using bacteria? ›

Bacteriapossess remarkable ability to reduce heavy metal ions and are one of the best candidates for nanoparticle synthesis. For instance, some bacterial species have developed the ability to resort to specific defense mechanisms to quell stresses like toxicity of heavy metal ions or metals.

What is the green synthesis of zinc? ›

angustifolia. During green synthesis of ZnONPs, the colour of the solution mixture of zinc nitrate hexahydrate and E. angustifolia leaf extract changed from light brown to yellowish black in colour. This colour change indicated the reduction of metallic zinc (Zn+) ions to zinc (ZnO) NPs.


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