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.
Highlights
Salinity is considered one of the most compelling environmental challenges encountered worldwide by the agricultural sector [1]
Exposing sorghum plants to salt stress significantly (p ≤ 0.05) reduced the growth parameters compared to the unstressed plants (Figure 1)
From the result of this study, we can conclude that ALA can induce tolerance to salinity stress in sorghum plants
Summary
Salinity is considered one of the most compelling environmental challenges encountered worldwide by the agricultural sector [1]. Salt stress can cause significant damage to biodiversity, ecosystems, human health, and natural resources [2]. Nowadays, this problem has been exacerbated in several regions of the world due to the adverse impacts of human activities, frequent climate changes, scarcity of freshwater, and a limitation of arable lands [1,3]. In the few years, these areas are expected to increase with the exponential growth of the global population, threatening food security [1,4,5]. Achieving an increase in agricultural food production under saline conditions has become a critical area of concern
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