Abstract
Melatonin (MT; N-acetyl-5-methoxytryptamine) is a pleiotropic signaling molecule that has been demonstrated to play an important role in plant growth, development, and regulation of environmental stress responses. Studies have been conducted on the role of the exogenous application of MT in a few species, but the potential mechanisms of MT-mediated stress tolerance under salt stress are still largely unknown. In this study, naked oat seedlings under salt stress (150 mM NaCl) were pretreated with two different concentrations of MT (50 and 100 μM), and the effects of MT on the growth and antioxidant capacity of naked oat seedlings were analyzed to explore the regulatory effect of MT on salt tolerance. The results showed that pretreating with different concentrations of MT promoted the growth of seedlings in response to 150 mM NaCl. Different concentrations of MT reduced hydrogen peroxide, superoxide anion, and malondialdehyde contents. The exogenous application of MT also increased superoxide dismutase, peroxidase, catalase, and ascorbate peroxide activities. Chlorophyll content, leaf area, leaf volume, and proline increased in the leaves of naked oat seedlings under 150 mM NaCl stress. MT upregulated the expression levels of the lipid peroxidase genes lipoxygenase and peroxygenase, a chlorophyll biosynthase gene (ChlG), the mitogen-activated protein kinase genes Asmap1 and Aspk11, and the transcription factor genes (except DREB2), NAC, WRKY1, WRKY3, and MYB in salt-exposed MT-pretreated seedlings when compared with seedlings exposed to salt stress alone. These results demonstrate an important role of MT in the relief of salt stress and, therefore, provide a reference for managing salinity in naked oat.
Highlights
Soil salinization is a global ecological problem and one of the main factors leading to land desertification and degradation of arable land
When a plant is subjected to stress, the extracellular signals are amplified in the cell through a signal transduction pathway, such as mitogen-activated protein kinase (MAPK), which activates transcription factors (TFs) to bind downstream target genes and promotes the expression of related genes, thereby increasing the plants’ response to stress [4]
Mitogen-Activated Protein Kinase (MAPK) genes were sequentially identified in Arabidopsis thaliana, rice, maize, wheat, and barley [8,9,10,11,12], and one study suggested that the MAPK cascade pathway is transmitted from environmental stress through MAPK-mediated phosphorylation cascades to enhance signals, such as high salinity, low temperature, and drought stress, which reach the nucleus and regulate downstream gene expression, thereby inducing the plant stress response [13]
Summary
Soil salinization is a global ecological problem and one of the main factors leading to land desertification and degradation of arable land. Salt stress in response to soil salinization has become an important factor limiting plant growth and yield [1,2]. Naked oat (Avena nuda L.) is an annual herbaceous crop in the family Poaceae It is a unique food crop found in Chinese alpine regions. In recent years, naked oat has been the focus of attention by researchers with application prospects due to its extremely high nutritional value and healthcare functions. Abiotic stressors, such as drought and salt, directly limit the growth of naked oat, restricting effective utilization and development of the plant [20]. We hypothesized thatexogenous application of MT would enhance the antioxidant capacity of naked oat seedlings under NaCl stress and thereby enhancing the antioxidant capacity of naked oat seedlings under NaCl stress
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