Kinetin Capped Zinc Oxide Nanoparticles Improve Plant Growth and Ameliorate Resistivity to Polyethylene Glycol (PEG)-Induced Drought Stress in Vigna radiata (L.) R. Wilczek (Mung Bean)

Abstract

Plants are sessile and mostly exposed to various environmental stresses which hamper plant growth, development, and significantly decline its production. Drought stress is considered to be one of the most significant limiting factors for crop plants, notably in arid and semi-arid parts the world. Therefore, the present study aimed to evaluate the potential impact of different concentrations (10, 100, and 200 µg/mL) of kinetin capped zinc oxide nanoparticles (Kn-ZnONPs) on Vigna radiata (L.) R. Wilczek under varying levels (5%, 10%, 15%) of PEG-induced drought stress. ZnONPs were synthesized by a co-precipitation method using Zinc acetate as a precursor at pH-12, incinerated to 500 °C, and kinetin was used as a surface functionalizing agent. The resulting Kn-ZnONPs were characterized by various contemporary analytical techniques, including SEM, SEM-EDS, XRD, DLS, and Zeta potential and IR spectroscopy. Crystalline Kn-ZnONPs, with a zeta potential of 27.8 mV and a size of 67.78 nm, of hexagonal wurtzite structure and vibrational stretches associated with N-H, C-O, C-N, etc., were confirmed. PEG-induced drought stress significantly reduced the growth of V. radiata by declining the chlorophyll and carotenoid contents. Moreover, a significant decrease in the levels of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), soluble sugar contents, proline, protein contents, phenol, and tannin were observed compared to the control. However, the exogenous application of Kn-ZnONPs ameliorated all photosynthetic parameters by up-regulating the antioxidant defense system through the promotion of SOD, POD, CAT, and lipid peroxidation levels. The biochemical parameters, such as proteins, soluble sugars, and proline, were observed to be maximum in plants treated with 200 µg/mL Kn-ZnONPs under 5% drought stress. The application of Kn-ZnONPs also enhanced the total phenol contents, flavonoid, and tannin contents. In conclusion, the findings of this study demonstrate that the exogenous application of Kn-ZnONPs provides beneficial effects to V. radiata by attenuating the damaging effects of drought stress through the up-regulation of the antioxidant defense system and osmolytes. These results suggest that Kn-ZnONPs have potential as a novel approach to improve crop productivity under drought stress conditions.

Keywords: Kn-ZnONPs; PEG-induced drought stress; antioxidant enzymes; chlorophyll contents; mung bean.

Figure 1

Scanning electron microscopy (SEM) images (A–C) at various magnification and spatial resolution of 0.5 µm to 5 µm, Transmission electron Micrograph (TEM) of kinetin capped ZnONPs (D) and SEM-EDS showing elemental Zinc signals as core of Zinc-oxide nanoparticles at different keV (E).

Figure 2

Dynamic light scattered spectrogram (DLS) of Kn-ZnONPs showing mean hydrodynamic particles size of 53.2 nm (A) with a Zeta potential of 18.7 mV (B).

Figure 3

Fourier Transform Infrared (FT-IR) Spectroscopy of Kinetin, ZnONPs, and Kn-ZnONPs showing different vibration stretches at various wavenumbers cm⁻¹ corresponding to the groups associated with kinetin and helped in the binding/capping and stabilization of ZnONPs suspension.

Figure 4

X-ray powder diffractogram of Kn-ZnONPs (red) matching the standard ZnO diffractogram (blue) of PDF-100979, showing various intensities at different 2 Ɵ levels, correspond to various Bragg’s planes of hexagonal wurtzite lattice.

Figure 5

Showing the impact of priming of various doses of Kn-ZnONPs on various germination indices (GP, GI, and MDG) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 6

Showing the impact of priming of various doses of Kn-ZnONPs on various germination indices (MGT and Co-VG) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 7

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on shoot length (cm) and fresh and dry biomasses (g) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 8

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on root length (cm) and fresh and dry biomasses (g) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 9

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on number of leaves per plant and leaf area (cm²) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 10

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on total chlorophyll and chlorophyll a and b (mg/g FW) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 11

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on carotenoids and anthocyanin contents (mg/g FW) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 12

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on various osmolytes (Sugar, protein, and proline in mg/g FW) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 13

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on the activity of antioxidant enzymes (SOD, POD, and CAT in IU min⁻¹ g⁻¹) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 14

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on the activity of antioxidant enzymes (APX, PPO IU min⁻¹ g⁻¹ and MDA in µmol g⁻¹) of V. radiata grown under different levels of PEG-induced drought stress.

Figure 15

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on free radical scavenging (H₂O₂ and DPPH) potential of V. radiata grown under different levels of PEG-induced drought stress.

Figure 16

Showing the effect of priming and foliar application of various doses of Kn-ZnONPs on total phenolic and tannin content of V. radiata grown under different levels of PEG-induced drought stress.