The excessive accumulation of copper (Cu²⁺) has become a threat to worldwide crop production. Recently, it was revealed that melatonin (MT) could play a crucial role against heavy metal (HM) stresses in plants. However, the underlying mechanism of MT function acted upon by Cu²⁺ stress (CS) has not been substantiated in tomatoes. In the present work, we produced MT-rich tomato plants by foliar usage of MT, and MT-deficient tomato plants by employing a virus-induced gene silencing methodology and exogenous foliar application of MT synthesis inhibitor para-chlorophenylalanine (pCPA). The obtained results indicate that exogenous MT meaningfully alleviated the dwarf phenotype and impeded the reduction in plant growth caused by excess Cu²⁺. Furthermore, MT effectively restricted the generation of reactive oxygen species (ROS) and habilitated cellular integrity by triggering antioxidant enzyme activities, especially via CAT and APX, but not SOD and POD. In addition, MT increased nonenzymatic antioxidant activity, including FRAP and the GSH/GSSG and ASA/DHA ratios. MT usage improved the expression of several defense genes (CAT, APX, GR and MDHAR) and MT biosynthesis-related genes (TDC, SNAT and COMT). Taken together, our results preliminarily reveal that MT alleviates Cu²⁺ toxicity via ROS scavenging, enhancing antioxidant capacity when subjected to excessive Cu²⁺. These results build a solid foundation for developing new insights to solve problems related to CS.

As a glycophyte plant, pepper (Capsicum annuum L.) is widely cultivated worldwide, but its growth is susceptible to salinity damage, especially at the seedling stage. Here, we conducted a study to determine the physiological and transcriptional differences between two genotype seedlings (P300 and 323F3) with contrasting tolerance under salt stress. The P300 seedlings were more salt-tolerant and had higher K⁺ contents, higher antioxidase activities, higher compatible solutes, and lower Na⁺ contents in both their roots and their leaves than the 323F3 seedlings. During RNA-seq analysis of the roots, more up-regulated genes and fewer down-regulated genes were identified between salt-treated P300 seedlings and the controls than between salt-treated 323F3 and the controls. Many ROS-scavenging genes and several SOS pathway genes were significantly induced by salt stress and exhibited higher expressions in the salt-treated roots of the P300 seedlings than those of 323F3 seedlings. Moreover, biosynthesis of the unsaturated fatty acids pathway and protein processing in the endoplasmic reticulum pathway were deeply involved in the responses of P300 to salt stress, and most of the differentially expressed genes involved in the two pathways, including the genes that encode mega-6 fatty acid desaturases and heat-shock proteins, were up-regulated. We also found differences in the hormone synthesis and signaling pathway genes in both the P300 and 323F3 varieties under salt stress. Overall, our results provide valuable insights into the physiological and molecular mechanisms that affect the salt tolerance of pepper seedlings, and present some candidate genes for improving salt tolerance in pepper.

The oomycete Phytophthora capsici causes Phytophthora blight, a major constraint on global pepper production. Our previous observations indicated that pretreating plants with thiamethoxam (TMX) and imidacloprid (IMI) could reduce the incidence of pepper blight, but the underlying mechanisms remained unclear. Here, we investigated how TMX and IMI induced resistance in pepper ( Capsicum frutescens ) against P. capsici . Both in vitro and in vivo assays demonstrated that TMX and IMI suppressed disease, not by directly impairing pathogen virulence but by inducing systemic resistance in susceptible (Cusheng L09) and resistant (Cusheng 356) pepper cultivars. Split‐plant systemic resistance assays showed that TMX/IMI‐primed plants developed smaller lesions in both treated and untreated leaves following P. capsici infection. Foliar application of TMX and IMI effectively alleviated disease severity, with IMI showing superior efficacy in attenuating reactive oxygen species (ROS) accumulation, and TMX/IMI priming concomitantly altering the activities of ROS‐scavenging enzymes under pathogen challenge. Reverse transcription‐quantitative PCR analysis revealed time‐dependent changes in defence gene expression, and whole‐genome transcriptome profiling highlighted temporal reprogramming of pathogenesis‐related genes. Further functional validation identified CaNEN4 as a susceptibility factor. Collectively, our findings reveal that IMI/TMX primes pepper plants with systemic resistance by modulating ROS homeostasis, defence gene expression, and susceptibility gene function, offering novel insights into chemical‐induced plant immunity and genetic targets for durable blight resistance in crops.

Blackleg, a devastating bacterial disease primarily caused by Pectobacterium carotovorum, poses a considerable threat to potato production. Accordingly, it is critical for the development of resistant cultivars to elucidate the physiological bases of resistance. Here, the resistance of 12 potato cultivars to blackleg were evaluated, identifying two highly resistant cultivars, and three susceptible cultivars. High resistant varieties Zhongshu 170 and Zhongshu 316 exhibited significantly lower decay levels compared to susceptible varieties, including Houma, Hongdao, and Huashu No. 2. This study also investigates the variations in malondialdehyde (MDA), proline (Pro), and hydrogen peroxide (H₂O₂) content among potato varieties with different blackleg resistance levels. The results indicate that high susceptibility is associated with elevated MDA and Pro, consistent with severe membrane lipid peroxidation. By contrast, H₂O₂ levels did not align strictly with resistance rankings, suggesting genotype-specific ROS signaling and scavenging strategies. Detection of antioxidant enzyme activities after pathogen inoculation showed that the activities of superoxide dismutase (SOD) and peroxidase (POD) in resistant varieties increased sharply post-inoculation. Additionally, catalase (CAT) and ascorbate peroxidase (APX) activities increased across all varieties after infection, with resistant types showing higher levels. Finally, the correlation analysis revealed a complex relationship between these indicators and disease resistance. Overall, this provides a scientific foundation for breeding programs aimed at developing potatoes with improved resistance to blackleg disease, ultimately enhancing agricultural strategies and production efficiency.