Complexation and immobilization of arsenic in maize using green synthesized silicon nanoparticles (SiNPs).

Arsenic (As) is a heavy metal that is toxic to both plants and animals. Silicon nanoparticles (SiNPs) can alleviate the detrimental effects of heavy metals on plants, but the underlying mechanisms remain unclear. The study aims to synthesize SiNPs and reveal how they promote plant health in Arsenic-polluted soil. 0 and 100% v/v SiNPs were applied to soil, and Arsenic 0 and 3.2 g/ml were applied twice. Maize growth was monitored until maturity. Small, irregular, spherical, smooth, and non-agglomerated SiNPs with a peak absorbance of 400 nm were synthesized from Pycreus polystachyos. The SiNPs (100%) assisted in the development of a deep, prolific root structure that aided hydraulic conductance and gave mechanical support to the maize plant under As stress. Thus, there was a 40-50% increase in growth, tripled yield weights, and accelerated flowering, fruiting, and senescence. SiNPs caused immobilization (As(III)=SiNPs) of As in the soil and induced root exudates Phytochelatins (PCs) (desGly-PC2 and Oxidized Glutathione) which may lead to formation of SiNPs=As(III)-PCs complexes and sequestration of As in the plant biomass. Moreover, SiNPs may alleviate Arsenic stress by serving as co-enzymes that activate the antioxidant-defensive mechanisms of the shoot and root. Thus, above 70%, most reactive ROS (OH) were scavenged, which was evident in the reduced MDA content that strengthened the plasma membrane to support selective ion absorption of SiNPs in place of Arsenic. We conclude that SiNPs can alleviate As stress through sequestration with PCs, improve root hydraulic conductance, antioxidant activity, and membrane stability in maize plants, and could be a potential tool to promote heavy metal stress resilience in the field.

Anatomical adaptation of water-stressed Eugenia uniflora using green synthesized silver nanoparticles and melatonin.

Cell and sub-cellular anatomical adjustments are adaptations utilized by plants to tolerate abiotic stress. Both melatonin and Morinda lucida-silver nanoparticles (ML-AgNPs) are recognized as bio-stimulants. The study examined the morphological changes and adaptive characteristics of these bio-stimulants under water-stress Eugenia uniflora. Twenty-four hours was spent priming the seeds with melatonin (0.06 mg/L), ML-AgNPs (0.06 mg/L), and a mixture (1:1) of the two. The seeds were sown and subjected to water stress for 7 days. The leaves, stems, and roots of water-stressed E. uniflora were sectioned, dried, and examined using a microscope. Drought stress led to the production of non-glandular trichomes on the abaxial and the transformation of paracytic stomata into diacytic stomata. During water stress, melatonin enlarges intercellular gaps and stomata, increases sponge and palisade parenchyma, and thickens epidermis (stem and root) and fibers. The ML-AgNPs diminished the size of mesophyll, intercellular gaps, stomata, and stem fiber. The ML-AgNPs increased the size of bulliform cells and activated the mechanical resistance features of sclerophyllous leaves (thick-celled epidermis and sclerieds) and ray parenchyma (root and stem). Equally, Melatonin and ML-AgNPs increased stem and root anatomical characteristics (xylem, bark, pith, cortex, epidermis, and vascular bundles). Stomata of E. uniflora are susceptible to alterations and undergo cell division into two new stomata (stomatogensis) in response to varying conditions (melatonin and ML-AgNPs). Melatonin adopted a strategy for maintaining a high plant water status, possibly by osmoregulation, whereas E. uniflora primed with ML-AgNPs survived by minimizing transpirational water loss through morphological changes.

Green synthesis and characterization of silver nanoparticles using Morinda lucida leaf extract and evaluation of its antioxidant and antimicrobial activity.

This study emphasizes the production of eco-friendly silver nanoparticles from a medicinal plant extract of Morinda lucida (M. lucida) and investigated its antioxidant and antimicrobial activity. Phytochemical screening of M. lucida (ML) leave extract was carried out and observed to contain some fundamental phyto-reducing agents such as reducing sugar, proteins, and alkaloids. The green synthesized AgNPs (ML-AgNPs) were characterized by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission emission microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Energy dispersive X-ray analysis (EDX). Thermo gravimetric analysis (TGA) was performed on the synthesized ML-capped AgNPs to determine the thermal stability and the formation of the green synthesized AgNPs. The formation of AgNPs was confirmed by the UV-vis absorption spectra, which showed an absorption band at 420 nm. The morphology of ML extract-mediated AgNPs was mostly spherical and rough-edged crystallite nanostructures, with an average particle size of 11 nm. The FTIR analyses revealed distinctive functional groups which were directly involved in the synthesis and stability of AgNPs. The crystallite size was 8.79 nm, with four intense peaks at 2θ angles of 38°, 44°, 64°, and 77°. At an energy level of 3.4 keV, a significant signal was observed indicating the production of thermally stable and pure crystallite AgNPs. The antioxidant property of green synthesized ML-AgNPs was determined to be 40% higher than that of crude M. lucida leaf extract. The ability of green synthesized ML-AgNPs to scavenge free radicals also increased in the order of OH- < NO < H2O2. The ML-AgNPs have strong activities with a maximum against P. vulgaris and a minimum with E. faecalis.