Melatonin mediates selenium‐induced tolerance to cadmium stress in tomato plants

Abstract

Both selenium (Se) and melatonin reduce cadmium (Cd) uptake and mitigate Cd toxicity in plants. However, the relationship between Se and melatonin in Cd detoxification remains unclear. In this study, we investigated the influence of three forms of Se (selenocysteine, sodium selenite, and sodium selenate) on the biosynthesis of melatonin and the tolerance against Cd in tomato plants. Pretreatment with different forms of Se significantly induced the biosynthesis of melatonin and its precursors (tryptophan, tryptamine, and serotonin); selenocysteine had the most marked effect on melatonin biosynthesis. Furthermore, Se and melatonin supplements significantly increased plant Cd tolerance as evidenced by decreased growth inhibition, photoinhibition, and electrolyte leakage (EL). Se-induced Cd tolerance was compromised in melatonin-deficient plants following tryptophan decarboxylase (TDC) gene silencing. Se treatment increased the levels of glutathione (GSH) and phytochelatins (PCs), as well as the expression of GSH and PC biosynthetic genes in nonsilenced plants, but the effects of Se were compromised in TDC-silenced plants under Cd stress. In addition, Se and melatonin supplements reduced Cd content in leaves of nonsilenced plants, but Se-induced reduction in Cd content was compromised in leaves of TDC-silenced plants. Taken together, our results indicate that melatonin is involved in Se-induced Cd tolerance via the regulation of Cd detoxification.

Overexpression of rice serotonin N‐acetyltransferase 1 in transgenic rice plants confers resistance to cadmium and senescence and increases grain yield

“…To evaluate the link between cadmium tolerance and cadmium contents in OsSNAT1 transgenic plants, we quantified cadmium levels and found that cadmium contents in the OsSNAT1 transgenic plants were comparable to those of the wild‐type controls, although line 3 showed a reduced cadmium level relative to wild type. These data suggested that cadmium tolerance in the OsSNAT1 transgenic rice leaves may be due to the direct antioxidative activity of melatonin or indirect enhancing effects on antioxidant enzymes, as described previously . Furthermore, we determined the expression levels of several genes responsible for cadmium tolerance, including low cadmium ( LCD ), ABC‐type transporter ( ABCG43 ), heat‐shock transcription factor ( HsfA4a ), and metallothionein ( MT1‐1a ), in wild‐type and OsSNAT1 transgenic plants to examine whether these genes are associated with cadmium tolerance.…”

“…In addition, the OsSNAT1 transgenic and wild‐type seedlings were equally susceptible to selenium treatment (Figure C,D). These observations indicated that selenium does not induce melatonin synthesis and that selenium toxicity is not alleviated by increases in endogenous melatonin levels in rice plants, in contrast to tomato plants …”

“…Li et al . reported that selenium induces melatonin biosynthesis in tomato plants as effectively as cadmium.…”

“…In addition to the defense responses, melatonin has also been implicated in promoting plant growth processes, such as seedling growth, flowering, nutrient absorption, and fruit ripening, suggesting a potential role of melatonin as a plant growth factor . Recently, the relationship between melatonin and cadmium has been a focus of attention because melatonin treatment not only attenuated the toxic effects of cadmium stress in tomato and rice, but melatonin levels were shown to be upregulated in response to cadmium to such an extent that this heavy metal is the most effective elicitor of melatonin biosynthesis in plants . However, the physiological roles of exogenously applied melatonin in plants have to be judged with caution as a pharmacological dose of melatonin does not necessarily reflect the physiological levels of endogenous melatonin …”

Melatonin Has the Potential to Alleviate Cinnamic Acid Stress in Cucumber Seedlings

“…Although numerous recent studies have demonstrated that MT plays important roles in alleviating abiotic stresses in cucumber seedlings, such as, NaCl stress (Zhang et al, 2014; Wang L. Y. et al, 2016), water stress (Zhang et al, 2013), chilling stress (Balabusta et al, 2016; Zhao et al, 2016), high temperature stress (Xu, 2010), oxidative stress (Li et al, 2016), and nitrate stress (Zhang et al, 2017), little information is available regarding the effects of MT on plant growth under CA stress. In this study, therefore, we treated cucumber seeds and seedlings with/without MT under CA- or non-stress conditions, and then assessed cucumber seedling growth, morphology, and nutrient element and plant hormone content.…”