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BackgroundAcidic soils with a pH water below 5.5 occupy up to 40% of world's arable land. Aluminum (Al) toxicity and magnesium (Mg) deficiency often coexist in acidic soils, limiting crop production. In this study, we investigated a role of Mg in alleviation of Al stress in maize (Zea mays) by characterizing the growth responses, Al accumulation and the antioxidant properties of plants cultured hydroponically. MethodsPhysiological and molecular analyses were used to investigate the mechanisms of Mg governing the alleviation of Al-induced ROS production and root growth inhibition. ResultsAluminum (50 µM) decreased root growth and induced oxidative stress. Exogenously added millimolar concentrations of Mg significantly alleviated Al toxicity as evidenced by restoration of plant growth, suppression of Al uptake, and a decline in root H 2 O 2 concentration. Furthermore, the addition of Mg to the Al treatment solution enhanced the activities and expression of genes encoding superoxide dismutase, catalase and peroxidase compared to the Al-only treatment. ConclusionsThe results indicate that Mg plays a role in alleviation of Al toxicity, reduction of Al accumulation and protection from Al-induced oxidative stress through activation of antioxidative enzymes.

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Phytomelatonin is a pleiotropic signaling molecule that regulates plant growth, development, and stress response. In plant cells, phytomelatonin is synthesized from tryptophan via several consecutive steps that are catalyzed by tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acyltransferase (SNAT), and N-acetylserotonin methyltransferase (ASMT) and/or caffeic acid-3-O-methyltransferase (COMT). Recently, the identification of the phytomelatonin receptor PMTR1 in Arabidopsis has been considered a turning point in plant research, with the function and signal of phytomelatonin emerging as a receptor-based regulatory strategy. In addition, PMTR1 homologs have been identified in several plant species and have been found to regulate seed germination and seedling growth, stomatal closure, leaf senescence, and several stress responses. In this article, we review the recent evidence in our understanding of the PMTR1-mediated regulatory pathways in phytomelatonin signaling under environmental stimuli. Based on structural comparison of the melatonin receptor 1 (MT1) in human and PMTR1 homologs, we propose that the similarity in the three-dimensional structure of the melatonin receptors probably represents a convergent evolution of melatonin recognition in different species.

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