Melatonin Alleviates Chromium Toxicity in Maize by Modulation of Cell Wall Polysaccharides Biosynthesis, Glutathione Metabolism, and Antioxidant Capacity

Abstract

Melatonin, a pleiotropic regulatory molecule, is involved in the defense against heavy metal stress. Here, we used a combined transcriptomic and physiological approach to investigate the underlying mechanism of melatonin in mitigating chromium (Cr) toxicity in Zea mays L. Maize plants were treated with either melatonin (10, 25, 50 and 100 μM) or water and exposed to 100 μM K2Cr2O7 for seven days. We showed that melatonin treatment significantly decreased the Cr content in leaves. However, the Cr content in the roots was not affected by melatonin. Analyses of RNA sequencing, enzyme activities, and metabolite contents showed that melatonin affected cell wall polysaccharide biosynthesis, glutathione (GSH) metabolism, and redox homeostasis. During Cr stress, melatonin treatment increased cell wall polysaccharide contents, thereby retaining more Cr in the cell wall. Meanwhile, melatonin improved the GSH and phytochelatin contents to chelate Cr, and the chelated complexes were then transported to the vacuoles for sequestration. Furthermore, melatonin mitigated Cr-induced oxidative stress by enhancing the capacity of enzymatic and non-enzymatic antioxidants. Moreover, melatonin biosynthesis-defective mutants exhibited decreased Cr stress resistance, which was related to lower pectin, hemicellulose 1, and hemicellulose 2 than wild-type plants. These results suggest that melatonin alleviates Cr toxicity in maize by promoting Cr sequestration, re-establishing redox homeostasis, and inhibiting Cr transport from the root to the shoot.

Impact of Exogenous Melatonin Application on Photosynthetic Machinery under Abiotic Stress Conditions

“…Furthermore, the supplementation in maize plants resulted in a higher photosynthetic rate, increases in chlorophyll content, and improvement in antioxidant enzyme synthesis, effectively mitigating Cr toxicity. The research also explored the role of melatonin in regulating the heavy metal binding ability of the cell wall, further contributing to enhanced stress tolerance [ 107 ].…”

Physiological and Transcriptomic Analysis Reveals That Melatonin Alleviates Aluminum Toxicity in Alfalfa (Medicago sativa L.)

“…Melatonin, an endogenous molecule with high conservation across eukaryotic evolution, plays a pivotal role as a signaling molecule in various biological processes and responses to abiotic stress in plants. These stresses include salt stress [33,34], drought stress [47], and heavy metal stress in certain species [35][36][37]. Recent studies have also revealed that melatonin mitigates Al toxicity in soybean [38], wheat [39], and maize [40,41] through diverse mechanisms.…”

“…One of the most extensively characterized and studied roles of melatonin is its ability to enhance plant tolerance to various abiotic stresses. For instance, exogenous melatonin has been shown to improve salt tolerance in sunflower [33] and rice [34], it plays a crucial role in mitigating the toxicity of heavy metals, and it alleviates cadmium toxicity in Chinese cabbage seedlings [35], chromium toxicity in maize [36], and copper toxicity in cucumber [37]. Researchers have also explored the potential alleviating effects of melatonin on Al toxicity.…”

“…Melatonin is well-known for its ability to enhance plant resistance to various abiotic stresses, including heavy metal stress [35][36][37], drought [41], and salt stress [34], primarily due to its potent free radical scavenging capabilities. Therefore, we sought to validate the mitigating effects of melatonin on cellular oxidative damage by assessing H 2 O 2 levels, malondialdehyde (MDA) content, and root cell vitality, which are indicative of Al-induced oxidative damage.…”

Exogenous Melatonin Promotes Glucoraphanin Biosynthesis by Mediating Glutathione in Hairy Roots of Broccoli (Brassica oleracea L. var. italica Planch)

“…According to the transcriptomic and proteomic data, this study found that exogenous MT increased the GSH content and GR activity in hairy roots (Figure 5). It has been shown that using melatonin to alleviate cadmium stress in maize increased GSH content [35], while the use of melatonin alleviated Cd stress and enhanced GR activity [36]. Wang et al (2012) found that melatonin increased the concentration of GSH by stimulating the activity of γ-glutamylcysteine synthetase, thereby delaying the senescence of apple leaves [37].…”