Exogenous Application of Alpha-Lipoic Acid Mitigates Salt-Induced Oxidative Damage in Sorghum Plants through Regulation Growth, Leaf Pigments, Ionic Homeostasis, Antioxidant Enzymes, and Expression of Salt Stress Responsive Genes

Montaser H M Youssef; Aly Raafat; Ahmed Abou El-Yazied; Samy Selim; Ehab Azab; Ebtihal Khojah; Nihal El Nahhas; Mohamed F M Ibrahim

doi:10.3390/plants10112519

Exogenous Application of Alpha-Lipoic Acid Mitigates Salt-Induced Oxidative Damage in Sorghum Plants through Regulation Growth, Leaf Pigments, Ionic Homeostasis, Antioxidant Enzymes, and Expression of Salt Stress Responsive Genes

Plants (Basel). 2021 Nov 19;10(11):2519. doi: 10.3390/plants10112519.

Authors

Montaser H M Youssef¹, Aly Raafat¹, Ahmed Abou El-Yazied², Samy Selim³, Ehab Azab⁴, Ebtihal Khojah⁴, Nihal El Nahhas⁵, Mohamed F M Ibrahim¹

Affiliations

¹ Department of Agricultural Botany, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt.
² Department of Horticulture, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt.
³ Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, Jouf University, Sakaka 2014, Saudi Arabia.
⁴ Department of Food Science and Nutrition, College of Sciences, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia.
⁵ Botany and Microbiology Department, Faculty of Science, Alexandria University, Alexandria 21515, Egypt.

Abstract

In plants, α-Lipoic acid (ALA) is considered a dithiol short-chain fatty acid with several strong antioxidative properties. To date, no data are conclusive regarding its effects as an exogenous application on salt stressed sorghum plants. In this study, we investigated the effect of 20 µM ALA as a foliar application on salt-stressed sorghum plants (0, 75 and 150 mM as NaCl). Under saline conditions, the applied-ALA significantly (p ≤ 0.05) stimulated plant growth, indicated by improving both fresh and dry shoot weights. A similar trend was observed in the photosynthetic pigments, including Chl a, Chl b and carotenoids. This improvement was associated with an obvious increase in the membrane stability index (MSI). At the same time, an obvious decrease in the salt induced oxidative damages was seen when the concentration of H₂O₂ and malondialdehyde (MDA) was reduced in the salt stressed leaf tissues. Generally, ALA-treated plants demonstrated higher antioxidant enzyme activity than in the ALA-untreated plants. A moderate level of salinity (75 mM) induced the highest activities of superoxide dismutase (SOD), guaiacol peroxidase (G-POX), and ascorbate peroxidase (APX). Meanwhile, the highest activity of catalase (CAT) was seen with 150 mM NaCl. Interestingly, applied-ALA led to a substantial decrease in the concentration of both Na and the Na/K ratio. In contrast, K and Ca exhibited a considerable increase in this respect. The role of ALA in the regulation of K⁺/Na⁺ selectivity under saline condition was confirmed through a molecular study (RT-PCR). It was found that ALA treatment downregulated the relative gene expression of plasma membrane (SOS1) and vacuolar (NHX1) Na⁺/H⁺ antiporters. In contrast, the high-affinity potassium transporter protein (HKT1) was upregulated.

Keywords: Sorghum bicolor L. moench; salinity; transporter proteins and oxidative stress; α-lipoic acid.