Abstract
This report focuses on the application of zinc oxide nanoparticles (ZnO NPs) carrying phycomolecule ligands as a novel plant growth promoter aimed at increasing the crop productivity of purslane (<em>Portulaca oleracea</em> L.). Experiments were performed under controlled greenhouse conditions using a completely randomized design with nine replications. Purslane seeds were treated with four concentrations of ZnO NPs (0, 10, 100, and 500 mg L<sup>−1</sup>) and four concentrations of bulk ZnO (0, 10, 100, and 500 mg L<sup>−1</sup>). The ultrastructural characteristics of the leaves of the plants treated with of 500 mg L<sup>−1</sup> ZnO NPs were determined using transmission electron microscopy (TEM). The results indicated that the treatment with ZnO NPs increased the content of chlorophyll <em>a</em> and chlorophyll <em>b</em>, carotenoids, and total phenolic and flavonoid compounds significantly more than the treatment with bulk ZnO. Our findings also showed that the application of high concentrations of ZnO NPs is the most effective strategy to considerably induce the antioxidant capacity and enzymes of purslane plants. Furthermore, the seed germination percentage and sprout growth rates were significantly higher in the plants treated with 500 mg L<sup>−1</sup> of ZnO NPs (100% ±0.00), compared to the control plants (93.33% ±1.66). The TEM images revealed the concentration of ZnO NPs and cell membrane rupture, as well as a deformation in the shape of chloroplasts and a decrease in their number in the plants treated with 500 mg L<sup>−1</sup> ZnO NPs, compared to the control plants. Owing to their toxicity, high concentrations of ZnO NPs lead to oxidative stress in plants. Thus, our findings provide a new alternative strategy for increasing crop productivity, i.e., the application of ZnO NPs as a novel plant growth booster, in comparison with the bulk ZnO treatment.
Highlights
Purslane (Portulaca oleracea L.) belongs to the family Portulacaceae
The statistical results showed that the root length increased in the groups treated with both zinc oxide nanoparticles (ZnO NPs) and bulk ZnO compared to the control group
The highest stem length was observed in the group treated with 500 mg L−1 of ZnO NPs, and it was significantly higher than that observed in the control group (p < 0.05)
Summary
Purslane (Portulaca oleracea L.) belongs to the family Portulacaceae It is the eighth most commonly known herb in the world [1]. It grows in cultivated fields, gardens, and waste places. The leaves and stems of this plant are edible and are used as a vegetable in many parts of the world [4,5]. Important scientific discoveries are being made on this medicinal plant, as it has been designated as a global elixir by the World Health Organization (WHO). It is the most common medicinal plant used by this organization [6]. Owing to its antioxidant properties and high nutrient levels, purslane is referred to as the “power food of the future” [7,8]
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