Exogenous Application of Salicylic Acid and Hydrogen Peroxide Ameliorate Cadmium Stress in Milk Thistle by Enhancing Morpho-Physiological Attributes Grown at Two Different Altitudes

Mereen Nizar; Kanval Shaukat; Noreen Zahra; Muhammad Bilal Hafeez; Ali Raza; Abdul Samad; Qasim Ali; Manzer H Siddiqui; Hayssam M Ali

doi:10.3389/fpls.2021.809183

Exogenous Application of Salicylic Acid and Hydrogen Peroxide Ameliorate Cadmium Stress in Milk Thistle by Enhancing Morpho-Physiological Attributes Grown at Two Different Altitudes

Front Plant Sci. 2022 Jan 27:12:809183. doi: 10.3389/fpls.2021.809183. eCollection 2021.

Authors

Mereen Nizar¹, Kanval Shaukat^{1

2}, Noreen Zahra², Muhammad Bilal Hafeez³, Ali Raza⁴, Abdul Samad¹, Qasim Ali⁵, Manzer H Siddiqui⁶, Hayssam M Ali⁶

Affiliations

¹ Department of Botany, University of Balochistan, Quetta, Pakistan.
² Department of Botany, University of Agriculture, Faisalabad, Pakistan.
³ Department of Agronomy, University of Agriculture, Faisalabad, Pakistan.
⁴ Key Laboratory of Ministry of Education for Genetics, Breeding and Multiple Utilization of Crops, Center of Legume Crop Genetics and Systems Biology/College of Agriculture, Oil Crops Research Institute, Fujian Agriculture and Forestry University (FAFU), Fuzhou, China.
⁵ Institute of Food and Agriculture Sciences, University of Florida, Gainesville, FL, United States.
⁶ Department of Botany and Microbiology, College of Science, King Saud University, Riyadh, Saudi Arabia.

Abstract

Cadmium (Cd⁺²) is a potential and widespread toxic environmental pollutant, mainly derived from a rapid industrial process that has inhibitory effects on growth, physiological, and biochemical attributes of various plant species, including medicinal plants such as Silybum marianum L. Gaertn commonly known as milk thistle. Plant signaling molecules, when applied exogenously, help to enhance/activate endogenous biosynthesis of potentially important signaling molecules and antioxidants that boost tolerance against various abiotic stresses, e.g., heavy metal stress. The present study documented the protective role of salicylic acid (SA;0.25 μM) and hydrogen peroxide (H₂O₂; 10 μM) priming, foliar spray, and combinational treatments in reducing Cd⁺² toxicity (500 μM) in milk thistle grown at two diverse ecological zones of Balochistan Province of Pakistan i.e., Quetta (Qta) and Turbat (Tbt). The morpho-physiological and biochemical attributes of milk thistle were significantly affected by Cd⁺² toxicity; however, priming and foliar spray of SA and H₂O₂ significantly improved the growth attributes (root/shoot length, leaf area, and root/shoot fresh and dry weight), photosynthetic pigments (Chl a, b, and carotenoids) and secondary metabolites (Anthocyanin, Soluble phenolics, and Tannins) at both altitudes by suppressing the negative impact of Cd⁺². However, the oxidative damage parameters, i.e., MDA and H₂O₂, decreased astonishingly under the treatment of signaling molecules, thereby protecting membrane integrity under Cd⁺² stress. The morphological variations were profound at the low altitude (Tbt) as compared to the high altitude (Qta). Interestingly, the physiological and biochemical attributes at both altitudes improved under SA and H₂O₂ treatments, thus hampered the toxic effect of Cd⁺². These signaling compounds enhanced tolerance of plants under heavy metal stress conditions with the consideration of altitudinal, and ambient temperature variations remain to be the key concerns.

Keywords: cadmium stress; chlorophyll; high altitude; milk thistle; oxidative damage.