Tannic acid-iron nanomaterial enhances rice growth and antioxidant defense under salt stress

Abstract

Salinity stress severely impacts plant growth by reducing water uptake and biomass accumulation, while nanomaterial applications have emerged as effective solutions. This study introduces tannic acid-iron nanomaterial (TA-Fe Nanomaterial), a biocompatible nanomaterial synthesized via self-assembly, as a novel solution to mitigate salt stress. Characterized by lamellar morphology (200 nm average size) and robust thermal stability, TA-Fe Nanomaterial demonstrated potent reactive oxygen species (ROS) scavenging capabilities. Under 100 mM NaCl stress, applying 25 μ g/mL TA-Fe Nanomaterial enhanced rice seed germination, increasing root length by 85% compared to salt-stressed controls. In the hydroponic experiment, treated seedlings exhibited 70% and 87% increases in underground and aboveground lengths, alongside 133% higher fresh weight. Soil-cultivated rice showed 43-88% improvements in biomass and 67% greater shoot length. Furthermore, applying TA-Fe Nanomaterial can alleviate the aberrant ROS accumulation in leaves under the conditions of salinity stress. These findings suggest that TA-Fe Nanomaterial could be a promising tool for enhancing rice tolerance to salt stress, paving the way for future applications in sustainable agriculture.

Keywords: nanomaterial; reactive oxygen species; rice; salt stress; sustainable agriculture.

Figure 1

Characterization of physicochemical properties of TA-Fe nanomaterial. (a) SEM image showing lamellar morphology. (b) TEM image. (c) FTIR spectrum confirms Fe-O bond formation (594 cm-¹). (d) TEM image of TA-Fe Nanomaterial and elemental mappings of C, N, O, and Fe, respectively. (e) TGA analysis showed the thermal stability of the material (onset of weight loss 672.7°C).

Figure 2

Broad-spectrum free radical scavenging ability of TA-Fe nanomaterial. (a) Effect of different concentrations of TA - Fe Nanomaterial on the absorbance of DPPH at 517 nm and (b) linear fit image with low concentration. (c) Inhibition rates and multiple comparisons (α = 0.05) of DPPH (86.36% inhibition rate at 100 μg/mL), (d) ·O₂ ^- (76.68% inhibition rate at 100 μg/mL), (e)·OH (77.21% inhibition rate at 100 μg/mL) and (f) H₂O₂ (26.72% inhibition rate at 100 μg/mL). (g) Effect of TA - Fe Nanomaterial concentration (from left to right, 0, 25, 50, 75 and 100 μg/mL) on the decomposition of H₂O₂ to produce oxygen bubbles. Error bars denote SD (n=3). Identical lowercase letters (e.g., a, a) indicate no significant difference (p > 0.05). Different lowercase letters (e.g., a, b) indicate statistically significant differences (p < 0.05).

Figure 3

TA-Fe nanomaterial mitigates the inhibition of salt stress on seed germination and root length in rice. (a) Effect of different concentrations of TA-Fe nanomaterial on root length of rice under salt stress (α = 0.05). (b) Photographs of germinated rice seeds (from left to right, Water, NaCl, NaCl + 12.5 μ g/mL TA - Fe Nanomaterial, NaCl + 25 μ g/mL TA - Fe Nanomaterial, NaCl + 50 μ g/mL TA - Fe Nanomaterial). Error bars denote SD (n=20). Identical lowercase letters (e.g., a, a) indicate no significant difference (p > 0.05). Different lowercase letters (e.g., a, b) indicate statistically significant differences (p < 0.05).

Figure 4

Regulation of growth parameters of hydroponic rice under salt stress by TA-Fe nanomaterial. (a) Fresh weight, (b) dry weight, (c) dry-to-fresh weight ratio and (d) length of the underground and aerial parts of hydroponic rice and multiple comparisons (α = 0.05) in the same part. (e) Promotional effect of TA-Fe nanomaterial on the growth of rice seedlings under salt stress (from top to bottom, Water, NaCl, NaCl + 12.5 μg/mL TA - Fe Nanomaterial, NaCl + 25 μg/mL TA - Fe Nanomaterial, NaCl + 50 μg/mL TA - Fe Nanomaterial, n=20). Error bars denote SD (n=6). Identical lowercase letters (e.g., a, a) indicate no significant difference (p > 0.05). Different lowercase letters (e.g., a, b) indicate statistically significant differences (p < 0.05).

Figure 5

TA-Fe nanomaterial enhances salt tolerance in rice by reducing oxidative damage. (a) Fresh weight, (b) dry weight, (c) dry-to-fresh weight ratio and (d) length of the underground and aerial parts of soil cultivated rice and multiple comparisons (α = 0.05) in the same part. (e) Percentage of EB staining seedlings (%). (f) Percentage of DAB staining seedlings (%). (g) Photographs during soil cultivation (from left to right, Water, NaCl, NaCl + 12.5 μg/mL TA - Fe Nanomaterial, NaCl + 25 μg/mL TA - Fe Nanomaterial, NaCl + 50 μg/mL TA - Fe Nanomaterial, n=20). (h) EB staining shows membrane damage in the salt stress group (dark blue) versus membrane integrity in the TA-Fe group (light blue). (i) DAB staining showed that TA-Fe treatment significantly reduced H₂O₂ accumulation (light yellow vs. dark brown in the salt stress group). Error bars denote SD (n=4). Identical lowercase letters (e.g., a, a) indicate no significant difference (p > 0.05). Different lowercase letters (e.g., a, b) indicate statistically significant differences (p < 0.05).