Cadmium (Cd) is one of the most injurious heavy metals, affecting plant growth and development. Melatonin (N-acetyl-5-methoxytryptamine) was discovered in plants in 1995, and it is since known to act as a multifunctional molecule to alleviate abiotic and biotic stresses, especially Cd stress. Endogenously triggered or exogenously applied melatonin re-establishes the redox homeostasis by the improvement of the antioxidant defense system. It can also affect the Cd transportation and sequestration by regulating the transcripts of genes related to the major metal transport system, as well as the increase in glutathione (GSH) and phytochelatins (PCs). Melatonin activates several downstream signals, such as nitric oxide (NO), hydrogen peroxide (H₂O₂), and salicylic acid (SA), which are required for plant Cd tolerance. Similar to the physiological functions of NO, hydrogen sulfide (H₂S) is also involved in the abiotic stress-related processes in plants. Moreover, exogenous melatonin induces H₂S generation in plants under salinity or heat stress. However, the involvement of H₂S action in melatonin-induced Cd tolerance is still largely unknown. In this review, we summarize the progresses in various physiological and molecular mechanisms regulated by melatonin in plants under Cd stress. The complex interactions between melatonin and H₂S in acquisition of Cd stress tolerance are also discussed.

Melatonin acts as a multifunctional molecule that takes part in various physiological processes, especially in the protection against abiotic stresses, such as salinity, drought, heat, cold, heavy metals, etc. These stresses typically elicit reactive oxygen species (ROS) accumulation. Excessive ROS induce oxidative stress and decrease crop growth and productivity. Significant advances in melatonin initiate a complex antioxidant system that modulates ROS homeostasis in plants. Numerous evidences further reveal that melatonin often cooperates with other signaling molecules, such as ROS, nitric oxide (NO), and hydrogen sulfide (H₂S). The interaction among melatonin, NO, H₂S, and ROS orchestrates the responses to abiotic stresses via signaling networks, thus conferring the plant tolerance. In this review, we summarize the roles of melatonin in establishing redox homeostasis through the antioxidant system and the current progress of complex interactions among melatonin, NO, H₂S, and ROS in higher plant responses to abiotic stresses. We further highlight the vital role of respiratory burst oxidase homologs (RBOHs) during these processes. The complicated integration that occurs between ROS and melatonin in plants is also discussed.

Polybrominated diphenyl ethers (PBDEs) are a group of flame retardants used in plastics, textiles, polyurethane foam, and other materials. They contain two halogenated aromatic rings bonded by an ester bond and are classified according to the number and position of bromine atoms. Due to their widespread use, PBDEs have been detected in soil, air, water, dust, and animal tissues. Besides, PBDEs have been found in various tissues, including liver, kidney, adipose, brain, breast milk and plasma. The continued accumulation of PBDEs has raised concerns about their potential toxicity, including hepatotoxicity, kidney toxicity, gut toxicity, thyroid toxicity, embryotoxicity, reproductive toxicity, neurotoxicity, and immunotoxicity. Previous studies have suggested that there may be various mechanisms contributing to PBDEs toxicity. The present study aimed to outline PBDEs’ toxic effects and mechanisms on different organ systems. Given PBDEs’ bioaccumulation and adverse impacts on human health and other living organisms, we summarize PBDEs’ effects and potential toxicity mechanisms and tend to broaden the horizons to facilitate the design of new prevention strategies for PBDEs-induced toxicity.

Large areas of arable lands in China have been contaminated by heavy metals, in which cadmium (Cd) contamination was the most prevalent. Cd accumulation in main food crops and leafy vegetables grown in Cd-contaminated fields has aroused considerable attention in recent years. The present study investigated the Cd pollution of farmland soils and vegetables in Qujing city of Yunnan Province, China. By comparing the Cd uptake capacities of different crops, this study aimed to provide guidance for agricultural production in Cd-contaminated farmland, and clarify the influence of Cd bioavailability in soil and chemical forms of Cd in plant roots on its migration. Results showed that soil Cd concentration was up to 37 mg kg⁻¹, which was 61-fold higher than the soil environmental quality standard in China. Concentration of Cd in 73% of the investigated vegetable samples, with the mean value of 5.43 mg Cd kg⁻¹ (dry weight basis), exceeded the food safety standard of China. Leafy vegetables had the highest bioaccumulation factors (BF) and transfer factors (TF), with the mean values of 0.53 and 0.41, respectively. Water spinach (Ipomoea aquatica Forsk.), cole (Brassica campestris L.), and fennel (Foeniculum dulce Mill.) had the highest Cd TFs, with averages of 0.67, 0.66, and 0.64, respectively. On the contrary, garlic (Allium sativum L.), onions (Allium fistulosum L.), and pea (Lathyrus odoratus L.) had the lowest Cd TFs, with averages of 0.04, 0.03, and 0.04, respectively. The main chemical fraction of Cd in garlic root was insoluble phosphate (35–48%), whereas in water spinach root, it was pectate, protein binding or sorbed fraction (50–64%), resulting in a higher TF value of water spinach than garlic. These results indicate that there were significant differences in Cd uptake and accumulation between vegetables, and the Cd accumulation in leafy vegetable was significantly higher than that in alliums. Therefore, it is possible to reduce the uptake and accumulation of Cd in crop edible parts by the selection of vegetable species with low Cd accumulation capacity. The chemical fractions of Cd in crop roots, especially the proportions of more mobile fractions, might be an important reason for the root-to-shoot Cd transport and Cd accumulation in the aerial portions.

The application amount of fertilizer is believed to dramatically influence soil bacteria in paddy fields, and soil bacteria critically affect soil enzyme activities and the growth of rice in paddy fields. Thus, providing a suitable amount of fertilization to ensure rice yields is an important issue in field management. In this study, four treatments were carried out in a paddy field, including control (fertilization methods commonly used by farmers in the past), IT + RF 10, IT + RF 20, and IT + RF 30 (integrated technology and 10%, 20%, and 30% reduction in nitrogen fertilizer, respectively). Soil samples were collected in two periods, the rice booting stage and the harvest period. High-throughput sequencing was used for analysis of soil bacterial diversity and community composition across different fertilizer treatments, and clarified the effects of different fertilizer treatments on soil enzyme activities and bacterial community composition. This study showed that a reduction in chemical fertilizer application has a certain impact on the soil pH, total nitrogen (TN), total phosphorus (TP), soil organic matter (SOM) value, and bacterial community of the rice planting system, and that the IT + RF 10 treatment was the best way to reduce fertilizer application, which can reduce nutrient loss in the paddy soil. The application of organic fertilizer partially replaces chemical fertilizer, which not only effectively stimulates soil enzyme activity, but also enriches bacterial groups that may participate in complex organic matter decomposition and soil nutrient mobilization.