Abstract
Melatonin improves the tolerance of plants to various environmental stresses by protecting plant cells against oxidative stress damage. The objective of the current study was to determine whether exogenous melatonin (MT) treatments could help protecting peanut (Arachis hypogaea) seedlings against salinity stress. This was achieved by investigating enzymatic and non-enzymatic antioxidant systems and the expression of melatonin biosynthesis related genes in response to salinity stress with or without exogenous MT. The results showed a significant increase in the concentrations of reactive oxygen species (ROS) in peanut seedlings under salinity stress. The exogenous application of melatonin decreased the levels of ROS through the activation of antioxidant enzymes in peanut seedlings under salinity stress. Transcription levels of melatonin biosynthesis related genes such as N-acetylserotonin methyltransferase (ASMT1, ASMT2, ASMT3), tryptophan decarboxylase (TDC), and tryptamine 5-hydroxylase (T5H) were up-regulated with a 150 µM melatonin treatment under salinity stress. The results indicated that melatonin regulated the redox homeostasis by its ability to induce either enzymatic or non-enzymatic antioxidant systems. In addition, phylogenetic analysis of melatonin biosynthesis genes (ASMT1, ASMT2, ASMT3, TDC, T5H) were performed on a total of 56 sequences belonging to various plant species including five new sequences extracted from Arachis hypogaea (A. hypogaea). This was based on pairwise comparison among aligned nucleotides and predicted amino acids as well as on substitution rates, and phylogenetic inference. The analyzed sequences were heterogeneous and the A. hypogaea accessions were primarily closest to those of Manihot esculenta, but this needs further clarification.
Highlights
Salinity stress is a major challenge to the agricultural sector impacting food security.Salinity stress results in harmful impacts on plant cells by either water shortfall triggered by Plants 2020, 9, 854; doi:10.3390/plants9070854 www.mdpi.com/journal/plantsPlants 2020, 9, 854 osmotic stress or the effect of excess sodium ions on key biochemical processes [1]
The current study focused on the phylogenetic relationships of four newly sequenced melatonin biosynthesis encoding genes amplified from A. hypogaea (ASMT1, 2, and 3, and tryptamine 5-hydroxylase (T5H)) as well as from other plant species whose sequences were retrieved from GenBank
Melatonin has emerged as a possible plant growth regulator, exogenously applied melatonin can enhance defense responses to different abiotic and biotic stress of plants by regulating both the enzymatic and non-enzymatic antioxidant defense systems [24,25,26,27,28,29]
Summary
Plants 2020, 9, 854 osmotic stress or the effect of excess sodium ions on key biochemical processes [1]. To limit these deleterious effects, plants utilize several biochemical and molecular strategies, such as synthesis of compatible osmolytes, induction of antioxidative enzymes, modification to the photosynthetic pathway, alterations in the membrane structure, and regulation of gene expression [2]. In order to alleviate the harmful effects of reactive oxidative stress, plants detoxify ROS either by activation of non-enzymatic antioxidants, such as carotenoids, glutathione (GSH), and ascorbic acid (AsA), or through the up-regulating of antioxidative enzymes including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), peroxiredoxins (Prxs), and glutathione peroxidase (GPX) [4]
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