Melatonin Enhances Drought Tolerance in Rice Seedlings by Modulating Antioxidant Systems, Osmoregulation, and Corresponding Gene Expression

Abstract

Rice is the third largest food crop in the world, especially in Asia. Its production in various regions is affected to different degrees by drought stress. Melatonin (MT), a novel growth regulator, plays an essential role in enhancing stress resistance in crops. Nevertheless, the underlying mechanism by which melatonin helps mitigate drought damage in rice remains unclear. Therefore, in the present study, rice seedlings pretreated with melatonin (200 μM) were stressed with drought (water potential of −0.5 MPa). These rice seedlings were subsequently examined for their phenotypes and physiological and molecular properties, including metabolite contents, enzyme activities, and the corresponding gene expression levels. The findings demonstrated that drought stress induced an increase in malondialdehyde (MDA) levels, lipoxygenase (LOX) activity, and reactive oxygen species (ROS, e.g., O2− and H2O2) in rice seedlings. However, the melatonin application significantly reduced LOX activity and the MDA and ROS contents (O2− production rate and H2O2 content), with a decrease of 29.35%, 47.23%, and (45.54% and 49.33%), respectively. It activated the expression of ALM1, OsPOX1, OsCATC, and OsAPX2, which increased the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), respectively. Meanwhile, the melatonin pretreatment enhanced the proline, fructose, and sucrose content by inducing OsP5CS, OsSUS7, and OsSPS1 gene expression levels. Moreover, the melatonin pretreatment considerably up-regulated the expression levels of the melatonin synthesis genes TDC2 and ASMT1 under drought stress by 7-fold and 5-fold, approximately. These improvements were reflected by an increase in the relative water content (RWC) and the root-shoot ratio in the drought-stressed rice seedlings that received a melatonin application. Consequently, melatonin considerably reduced the adverse effects of drought stress on rice seedlings and improved rice’s ability to tolerate drought by primarily boosting endogenous antioxidant enzymes and osmoregulation abilities.

Transcriptome and WGCNA reveal hub genes in sugarcane tiller seedlings in response to drought stress

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Characterizing stomatal attributes and photosynthetic induction in relation to biochemical changes in Coriandrum sativum L. by foliar-applied zinc oxide nanoparticles under drought conditions

“…A noticeable reduction was observed in IR50 plants when treated with NPs ( Khan et al., 2022 ). The possible phenomena may be the initiation of melatonin synthesis in C. sativum that improved the activity of antioxidant enzymes ( Luo et al., 2022 ). This may ameliorate the drought tolerance through a reduction in ABA and increasing the osmo-protectants (proline and chlorophyll content) as described by Luying Sun et al.…”

Exogenous Melatonin and Salicylic Acid Enhance the Drought Resistance of Hibiscus (Hibiscus syriacus L.) by Regulating Photosynthesis and Antioxidant System

“…Of them, soil drought is one of the most severe environmental stressors leading to a decrease in plant productivity. This decrease slows down plant growth or accelerates plant aging by affecting various plant physiological and biochemical processes (Luo et al 2022;Talbi et al 2020). Drought can cause plant chloroplast degradation, resulting in damage to the photosynthetic system, inhibition of photosynthetic electron transfer, an increase in excess excitation energy, and ultimately accumulation of reactive oxygen species (ROS) in the chloroplast.…”