Effects of SNP, MgSO4, and MgO-NPs foliar application on Spinacia oleracea L. growth and physio-biochemical responses under cadmium stress

Abstract

The effects of foliar application of sodium nitroprusside (SNP), magnesium sulfate (MgSO₄) and magnesium oxide nanoparticles (MgO-NPs) on the growth, physiology, and gas exchange parameters of two varieties of spinach (Spinacia oleracea L.) under cadmium (Cd) stress were examined. The experiment was arranged in a completely randomized design with 72 pots. Two varieties of S. oleracea (Desi Palak & Lahori Palak) were used. Two concentrations of Cd (0 µM and 150 µM) in the form of cadmium chloride (CdCl₂) were used. Two levels of SNP (0 ppm and 100 ppm) and two levels for each form of Mg i.e. MgSO₄ and MgO-NPs (0 and 200 ppm) were foliar sprayed on plants in control and Cd stress. Both varieties behaved similarly under Cd stress and caused reductions in growth, physiology, gas exchange, water content parameters and inorganic ion uptake. However, the biochemical parameters like relative membrane permeability (RMP), malondialdehyde (MDA), and hydrogen peroxide (H₂O₂) contents were increased. However, all foliar spray treatments increased growth, physiological and gas exchange parameters, water content and inorganic ion uptake. However, this reduced the MDA, RMP, and H₂O₂ contents. Desi Palak showed the more positive results under foliar application of MgO-NPs. However, Lahori palak showed more positive results under the SNP + MgO-NP treatment. It is concluded that foliar application of SNP, MgSO₄ and MgO-NPs could be an innovative approach to alleviated the heavy metals (Cd) toxicity in crop plants.

Fig. 1

Spinaceae oleraceae L. (Variety- Lahori Palak) plant. Control plant (Cd1S1Mg0), SNP (Cd1S2Mg0), MgSO₄ (Cd1S1Mg-I), MgO nanoparticles (Cd1S1Mg-II), SNP + MgSO₄ (Cd1S2Mg-I), SNP + MgO nanoparticles (Cd1S2Mg-II).

Fig. 2

Spinaceae oleraceae L. (Variety- Desi Palak) plant. Cd plant (Cd1S1Mg0), Cd + SNP (Cd2S2Mg0), Cd + MgSO₄ (Cd2S1Mg-I), Cd + MgO nanoparticles (Cd2S1Mg-II), Cd + SNP + MgSO₄ (Cd2S2Mg-I), Cd + SNP + MgO nanoparticles (Cd2S2Mg-II).

Fig. 3

Spinaceae oleraceae L. (Variety- Lahori Palak) plant. control plant (Cd1S1Mg0), SNP (Cd1S2Mg0), MgSO₄ (Cd1S1Mg-I), MgO nanoparticles (Cd1S1Mg-II), SNP + MgSO₄ (Cd1S2Mg-I), SNP + MgO nanoparticles (Cd1S2Mg-II).

Fig. 4

Spinaceae oleraceae L. (Variety- Lahori Palak) plant. Cd plant (Cd2S1Mg0), Cd + SNP (Cd2S2Mg0), Cd + MgSO₄ (Cd2S1Mg-I), Cd + MgO nanoparticles (Cd2S1Mg-II), Cd + SNP + MgSO₄ (Cd2S2Mg-I), Cd + SNP + MgO nanoparticles (Cd2S2Mg-II).

Fig. 5

Morphological features of two varieties of Spinacia oleraceae under Cadmium (Cd) stress and foliar applied Sodium nitroprusside (SNP), MgSO₄ (Mg-I), and MgO nanoparticles (Mg-II). A = Shoot fresh weight, B = Shoot dry weight, C = Root fresh weight and D = Root dry weight. Mean value is represented by data in A-D. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 6

Morphological parameter of two varieties of Spinacia oleraceae under Cadmium (Cd) stress and foliar applied Sodium nitroprusside (SNP), MgSO₄ (Mg-I), and MgO nanoparticles (Mg-II). A = Shoot length, B = Root length, C = Leaf count and D = Leaf area. Mean value is represented by data in A–D. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 7

Chlorophyll and carotenoides content of two varieties of Spinacia oleraceae under Cadmium (Cd) stress and foliar applied SNP, MgSO₄ (Mg-I) and MgO nanoparticles (Mg-II). A = Chlorophyll a, B = Chlorophyll b, C = Carotenoids and D = SPAD value. Mean value is represented by data in A-C. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 8

Chlorophyll fluorescence value of two varieties of Spinacia oleraceae under Cadmium (Cd) stress and foliar applied Sodium nitroprusside (SNP), MgSO₄ (Mg-I), and MgO nanoparticles (Mg-II). A = Variable flouresence (F_v), B = Maximal fluorescence (F_m), C = Maximum quantum yield of fluorescence (F_v/F_m), D = Minimal Flourescence (F_o), and E = F_v/F_o of fluorescence (F_v/F_m). Mean value is represented by data in A-C. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 9

Gas exchange parameters of two varieties of Spinacia oleraceae under Cadmium (Cd) stress and foliar applied Sodium nitroprusside (SNP), MgSO₄ (Mg-I), and MgO nanoparticles (Mg-II). A = Net Photosynthetic Rate (P_n), B = Stomatal Conductance (g_S), C = Intracellular CO₂ (C_i) and D = Transpiration Rate (T_n). Mean value is represented by data in A-D.Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 10

Relative membrane permeability and Water status of two varieties of Spinacia oleraceae under Cadmium (Cd) stress and foliar applied SNP, MgSO₄ (Mg-I) and MgO nanoparticles (Mg-II). A = Relative membrane permeability, B = Relative water content, C = Leaf water potential and D = Leaf osmotic potential. Mean value is represented by data in A-D. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 11

Effect of foliar application of SNP, MgSO₄ (Mg-I) and MgO nanoparticles (Mg-II) on A = Hydrogen peroxide, B = malondialdehyde and C = total soluble proteins in S. oleracea varieties under Cadmium (Cd) stress. Mean value is represented by data in A and B. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 12

Effect of foliar application of SNP, MgSO₄ (Mg-I) and MgO nanoparticles (Mg-II) on A = Catalase, B = Ascorbate peroxidase, C = Peroxidase and D = Superoxide dismutase activities in S. oleracea varieties under Cadmium (Cd) stress. Mean value is represented by data in A-D. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 13

Effect of foliar application of SNP, MgSO₄ (Mg-I) and MgO nanoparticles (Mg-II) on A = Leaf proline, and B = Total phenolics content in S. oleracea varieties under Cadmium (Cd) stress. Mean value is represented by data in A and B. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 14

Effect of foliar application of SNP, MgSO₄ (Mg-I) and MgO nanoparticles (Mg-II) on A = K⁺ ion shoots, B = Ca⁺ ion shoots, C = K⁺ ion roots and D = Ca⁺ ion roots of S. oleracea varieties under Cadmium (Cd) stress. Mean value is represented by data in A–D. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 15

Effect of foliar application of SNP, MgSO₄ (Mg-I) and MgO nanoparticles (Mg-II) on Cadmium (Cd), Iron (Fe) and Magnesium (Mg) content in S. oleracea varieties under Cadmium (Cd) stress. A = Shoot Cd content, B = Shoot Fe contentb, and C = Shoot Mg content. Mean value is represented by data in A–C. Standard error (SE) represented by error bars. Distinct letters (a, b, c, etc.) denote statistically significant variances among the treatment categories, identified by completely randomized four-way ANOVA followed by the LSD test having significance value p < 0.05.

Fig. 16

Pearson’s correlation for all studied attributes of S. oleracea plants under the effect of Cd toxicity with or without SNP, MgSO₄ and MgO-NPs foliar spray. Upper triangle is for variety Desi Palak and lower triangle is for variety Lahori Palak.

Fig. 17

Principal components analysis of all studied attributes of S. oleracea variety Desi Palak under the effect of Cd toxicity with or without SNP, MgSO₄ and MgO-NPs foliar spray. The arrow length showed the contribution of each attribute. Numbers 1, 2, 3…, 12 represents different treatments of SNP, MgSO₄ and MgO-NPs applied in control (1–6) and Cd stress (7–12) conditions.

Fig. 18

Principal components analysis of all studied attributes of S. oleracea variety Lahori Palak under the effect of Cd toxicity with or without SNP, MgSO₄ and MgO-NPs foliar spray. The arrow length showed the contribution of each attribute. Numbers 1, 2, 3…, 12 represents different treatments of SNP, MgSO₄ and MgO-NPs applied in control (1–6) and Cd stress (7–12) conditions.

Fig. 19

Growth of S. oleracea plants under Cd stress.

Fig. 20

NO, MgSO₄ and MgO-NPs entry mechanism, target sites and responses in plants.