Alpha Lipoic Acid as a Protective Mediator for Regulating the Defensive Responses of Wheat Plants against Sodic Alkaline Stress: Physiological, Biochemical and Molecular Aspects

Khaled M A Ramadan; Maha Mohammed Alharbi; Asma Massad Alenzi; Hossam S El-Beltagi; Doaa Bahaa Eldin Darwish; Mohammed I Aldaej; Tarek A Shalaby; Abdallah Tageldein Mansour; Yasser Abd El-Gawad El-Gabry; Mohamed F M Ibrahim

doi:10.3390/plants11060787

Alpha Lipoic Acid as a Protective Mediator for Regulating the Defensive Responses of Wheat Plants against Sodic Alkaline Stress: Physiological, Biochemical and Molecular Aspects

Plants (Basel). 2022 Mar 16;11(6):787. doi: 10.3390/plants11060787.

Authors

Affiliations

¹ Central Laboratories, Department of Chemistry, King Faisal University, Al-Ahsa 31982, Saudi Arabia.
² Biochemistry Department, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt.
³ Biology Department, Faculty of Science, University of Tabuk, Tabuk 71491, Saudi Arabia.
⁴ Agricultural Biotechnology Department, College of Agriculture and Food Sciences, King Faisal University, Al-Ahsa 31982, Saudi Arabia.
⁵ Biochemistry Department, Faculty of Agriculture, Cairo University, Gamma St, Giza 12613, Egypt.
⁶ Botany Department, Faculty of Science, Mansoura University, Mansoura 35511, Egypt.
⁷ Department of Arid Land Agriculture, College of Agricultural and Food Science, King Faisal University, P.O. Box 400, Al-Ahsa 31982, Saudi Arabia.
⁸ Horticulture Department, Faculty of Agriculture, Kafrelsheikh University, Kafr El-Sheikh 33516, Egypt.
⁹ Animal and Fish Production Department, College of Agricultural and Food Sciences, King Faisal University, P.O. Box 420, Al-Ahsa 31982, Saudi Arabia.
¹⁰ Fish and Animal Production Department, Faculty of Agriculture (Saba Basha), Alexandria University, Alexandria 21531, Egypt.
¹¹ Department of Agronomy, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt.
¹² Department of Agricultural Botany, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt.

Abstract

Recently, exogenous α-Lipoic acid (ALA) has been suggested to improve the tolerance of plants to a wide array of abiotic stresses. However, there is currently no definitive data on the role of ALA in wheat plants exposed to sodic alkaline stress. Therefore, this study was designed to evaluate the effects of foliar application by ALA at 0 (distilled water as control) and 20 µM on wheat seedlings grown under sodic alkaline stress (50 mM 1:1 NaHCO₃ & Na₂CO₃; pH 9.7. Under sodic alkaline stress, exogenous ALA significantly (p ≤ 0.05) improved growth (shoot fresh and dry weight), chlorophyll (Chl) a, b and Chl a + b, while Chl a/b ratio was not affected. Moreover, leaf relative water content (RWC), total soluble sugars, carotenoids, total soluble phenols, ascorbic acid, K and Ca were significantly increased in the ALA-treated plants compared to the ALA-untreated plants. This improvement was concomitant with reducing the rate of lipid peroxidation (malondialdehyde, MDA) and H₂O₂. Superoxide dismutase (SOD) and ascorbate peroxidase (APX) demonstrated greater activity in the ALA-treated plants compared to the non-treated ones. Conversely, proline, catalase (CAT), guaiacol peroxidase (G-POX), Na and Na/K ratio were significantly decreased in the ALA-treated plants. Under sodic alkaline stress, the relative expression of photosystem II (D2 protein; PsbD) was significantly up-regulated in the ALA treatment (67% increase over the ALA-untreated plants); while Δ pyrroline-5-carboxylate synthase (P5CS), plasma membrane Na⁺/H⁺ antiporter protein of salt overly sensitive gene (SOS1) and tonoplast-localized Na⁺/H⁺ antiporter protein (NHX1) were down-regulated by 21, 37 and 53%, respectively, lower than the ALA-untreated plants. These results reveal that ALA may be involved in several possible mechanisms of alkalinity tolerance in wheat plants.

Keywords: Triticum aestivum L.; high-pH; ionic homeostasis; osmolytes and qRT-PCR; oxidative damages.

Grants and funding

Grant 9/Deanship of Scientific Research, Vice Presidency for Graduate Studies and Scientific Research, King Faisal University, Saudi Arabia