Synergistic effects of Vachellia nilotica-derived zinc oxide nanoparticles and melatonin on drought tolerance in Fragaria × ananassa

Abstract

This study investigates the synergistic effects of zinc oxide nanoparticles (ZnO NPs) and melatonin (MT) on Fragaria × ananassa (strawberry) plants under drought stress, focusing on growth, fruit biomass, and stress tolerance. ZnO NPs enhance nutrient uptake and stress resistance, while MT regulates growth hormones and boosts photosynthetic efficiency. Seven treatments were evaluated: T1 (no stress, 0.5 g/L ZnO NPs + 0.1 g/L MT), T2 (no stress, 0.5 g/L ZnO NPs), T3 (no stress, 0.1 g/L MT), T4 (drought stress, no application), T5 (drought stress, 0.5 g/L ZnO NPs + 0.1 g/L MT), T6 (drought stress, 0.5 g/L ZnO NPs), and T7 (drought stress, 0.1 g/L MT). Growth and stress parameters included shoot/root length, fruit biomass, bud number, chlorophyll content, oxidative stress markers (H₂O₂, MDA), and antioxidant enzyme activities in the leaves of Fragaria × ananassa. The combined treatment (ZnO NPs + MT) consistently outperformed others, achieving the highest growth metrics under both conditions: shoot length (22.33 ± 1.53 cm non-stress, 15.00 ± 1.53 cm drought), root length (18.67 ± 1.53 cm non-stress, 12.00 ± 1.53 cm drought), and fruit biomass (9.55 ± 0.31 g non-stress, 5.02 ± 0.23 g drought). Bud formation peaked at 3.33 ± 0.58 buds/plant non-stress and 2.00 ± 0.00 buds/plant drought. Under drought, the combined treatment also enhanced chlorophyll content (2.47 ± 0.20 mg/g FW) and significantly reduced H₂O₂ (28.67 ± 2.52 µmol/g FW) and MDA (4.21 ± 0.10 µmol/g FW) levels, while maximizing antioxidant enzyme activities (SOD: 121.67 ± 7.64 U/g FW, POD: 206.33 ± 14.84 U/g FW, CAT: 48.00 ± 3.61 U/g FW). These findings highlight the combined application of ZnO NPs and MT as a promising strategy to enhance growth and stress tolerance in strawberry plants, warranting further research on optimized concentrations, delivery methods, and molecular mechanisms.

Keywords: Drought stress; Growth enhancement; Melatonin; Strawberry plants; ZnO nanoparticles.

Fig. 1

XRD spectra of (a) green and (b) chemically synthesized ZnO nanoparticles

Fig. 2

HR-TEM image of (a) green and (b) chemically synthesized ZnO nanoparticles

Fig. 3

UV–vis spectrum of green synthesized ZnO nanoparticles

Fig. 4

Bar plot of multiple comparisons of means (a) shoot length (cm), (b) root length (cm), (c) shoot biomass (g), (d) root biomass (g). Error bars represent the standard deviation of the mean of the data. Means with different letters are significantly different at alpha 0.05 from each other. Ctrl (control), MT (0.1 g/L melatonin), NPs (0.5 g/L ZnO NPs), NPs + MT (0.5 g/L ZnO NPs and 0.1 g/L Melatonin combined), drought is drought stress, MT + DT (0.1 g/L melatonin and drought), NPs + DT (0.5 g/L ZnO NPs and drought) and NPS + MT + DT (0.5 g/L ZnO NPs and 0.1 g/L melatonin and drought)

Fig. 5

Bar plot of multiple comparison of means (a) number of leaves, (b) number of rotten leaves, (c) leaf width (cm), (d) leaf length (cm). Error bars represent the standard deviation of the mean of the data. Means with different letters are significantly different at alpha 0.05 from each other. Ctrl (control), MT (0.1 g/L melatonin), NPs (0.5 g/L ZnO NPs), NPs + MT (0.5 g/L ZnO NPs and 0.1 g/L Melatonin combined), drought is drought stress, MT + DT (0.1 g/L melatonin and drought), NPs + DT (0.5 g/L ZnO NPs and drought) and NPS + MT + DT (0.5 g/L ZnO NPs and 0.1 g/L melatonin and drought)

Fig. 6

Bar plot of multiple comparisons of means (a) chlorophyll a content (mg/g FW), (b) chlorophyll b content (mg/g FW), (c) total chlorophyll content (mg/g FW). Error bars represent the standard deviation of the mean of the data. Means with different letters are significantly different at alpha 0.05 from each other. Ctrl (control), MT (0.1 g/L melatonin), NPs (0.5 g/L ZnO NPs), NPs + MT (0.5 g/L ZnO NPs and 0.1 g/L Melatonin combined), drought is drought stress, MT + DT (0.1 g/L melatonin and drought), NPs + DT (0.5 g/L ZnO NPs and drought) and NPS + MT + DT (0.5 g/L ZnO NPs and 0.1 g/L melatonin and drought)

Fig. 7

Bar plot of multiple comparisons of means (a) H2O2 (µmol/g FW), (b) MDA (µmol /g FW), (c) electrolyte leakage (%), (d) SOD, (e) POD, (f) CAT activity. Error bars represent the standard deviation of the mean of the data. Means with different letters are significantly different at alpha 0.05 from each other. Ctrl (control), MT (0.1 g/L melatonin), NPs (0.5 g/L ZnO NPs), NPs + MT (0.5 g/L ZnO NPs and 0.1 g/L Melatonin combined), drought is drought stress, MT + DT (0.1 g/L melatonin and drought), NPs + DT (0.5 g/L ZnO NPs and drought) and NPS + MT + DT (0.5 g/L ZnO NPs and 0.1 g/L melatonin and drought)

Fig. 8

Radar chart showing fruit biomass (FrW) (a) and number of buds (NOB) (b) under different treatments studied in the experiment. Ctrl (control), MT (0.1 g/L melatonin), NPs (0.5 g/L ZnO NPs), NPs + MT (0.5 g/L ZnO NPs and 0.1 g/L Melatonin combined), drought is drought stress, MT + DT (0.1 g/L melatonin and drought), NPs + DT (0.5 g/L ZnO NPs and drought) and NPS + MT + DT (0.5 g/L ZnO NPs and 0.1 g/L melatonin and drought)

Fig. 9

Pearson correlation for different growth attributes of strawberry plant in response to ZnO NPs and MT under drought stress. Intensity of blue color shows negative correlation while intensity of red color is showing positive correlation. NOL = number of leaves; LW = leaf area; LL = leaf length; NORL = number of rotten leaves; NOB = number of buds; H 2 O 2 = hydrogen peroxide content; EL = electrolyte leakage; Cha = chlorophyll a content; Chb = chlorophyll b content; Tchl = total chlorophyll; FrW = fruit biomass; SL = shoot length; RL = root length; PL = plant length; SW = shoot biomass; RW = root biomass; PW = plant biomass.