Mechanical injury to lettuce often leads to enzymatic browning caused by polyphenol oxidase (PPO), significantly impairing its sensory quality and processing suitability. In this study, the LsPPOs gene family was comprehensively identified and characterized using bioinformatics methods, including gene and protein structure, codon usage bias, phylogenetic relationships, and gene expression in response to wound stress. Further analysis of the relationship between LsPPOs expression profile and browning was performed. A total of 17 LsPPO family members (LsPPO1-LsPPO17) were identified from publicly available lettuce databases, encoding proteins ranging from 146 to 667 amino acids, with a G/C bias. Most were localized in the chloroplast. The motif structure was highly conserved among family members, and phylogenetic analysis revealed four distinct groups. All genes lacked introns, except LsPPO2 which contained an intron. After mechanical injury, browning at the stem site deepened over time, with PPO activity increasing. The majority of PPO members were significantly upregulated after fresh-cut processing. Among them, LsPPO3, LsPPO4, and LsPPO12 showed sustained upregulation, exhibiting a strong positive correlation with the browning phenotype and PPO activity. Notably, LsPPO4 demonstrated the highest transcriptional abundance and upregulation in response to a wound, indicating its major role in lettuce stem browning. The results of this study provide a foundation for further investigation into the functional role of LsPPOs and support the development of lettuce varieties with enhanced resistance to browning.

This study aims to comparatively analyze and evaluate the postharvest quality of tomatoes, and to further screen and utilize the excellent tomato germplasm resources. Correlation analysis, principal component analysis (PCA), and cluster analysis were performed on 18 appearance and nutritional quality indicators of 57 tomato F1 hybrids (labeled accession 1# to 57#). The results show that the variation coefficients of the tested quality indicators among tomato accessions ranged from 3.77% to 42.92%. Among them, 11 indicators had variation coefficients greater than 10%. The soluble protein content had the highest variation coefficient. Six principal components were extracted through PCA, accounting for 78.696% of the variability. The appearance indicators (size, single fruit weight, and a* value) and soluble solid content played key roles in tomato quality evaluation. According to the calculated comprehensive scores, the top 10 accessions with superior overall quality were selected from the tested tomato accessions. Cluster analysis divided the 57 tomato accessions into two major groups and seven subgroups. Notably, accession 6# showed the best flavor and nutritional quality, which could be a focus for future tomato breeding. These results provide a theoretical basis for comprehensive evaluation of tomato and quality improvement in tomato breeding.