With the expansion of the area under Cruciferae vegetable cultivation, and an increase in the incidence of natural threats such as pests and diseases globally, Cruciferae vegetable losses caused by pathogens, insects, and pests are on the rise. As one of the key metabolites produced by Cruciferae vegetables, glucosinolate (GLS) is not only an indicator of their quality but also controls infestation by numerous fungi, bacteria, aphids, and worms. Today, the safe and pollution-free production of vegetables is advocated globally, and environmentally friendly pest and disease control strategies, such as biological control, to minimize the adverse impacts of pathogen and insect pest stress on Cruciferae vegetables, have attracted the attention of researchers. This review explores the mechanisms via which GLS acts as a defensive substance, participates in responses to biotic stress, and enhances plant tolerance to the various stress factors. According to the current research status, future research directions are also proposed.

Melatonin plays key roles in improving fruit quality and yield by regulating various aspects of plant growth. However, the effects of how melatonin regulates primary and secondary metabolites during fruit growth and development are poorly understood. In this study, the surfaces of tomato fruit were sprayed with different concentrations of melatonin (0, 50, and 100 µmol·L⁻¹) on the 20th day after anthesis; we used high-performance liquid chromatography (HPLC) and liquid chromatography/mass spectrometry (LC/MS) to determine the changes in primary and secondary metabolite contents during fruit development and measured the activity of sucrose metabolizing enzymes during fruit development. Our results showed that 100 µmol·L⁻¹ melatonin significantly promoted the accumulation of soluble sugar in tomato fruit by increasing the activities of sucrose synthase (SS), sucrose phosphate synthase (SPS), and acid convertase (AI). The application of 100 µmol·L⁻¹ melatonin also increased the contents of ten amino acids in tomato fruit as well as decreased the contents of organic acids. In addition, 100 µmol·L⁻¹ melatonin application also increased the accumulation of some secondary metabolites, such as six phenolic acids, three flavonoids, and volatile substances (including alcohols, aldehydes, and ketones). In conclusion, melatonin application improves the internal nutritional and flavor quality of tomato fruit by regulating the accumulation of primary and secondary metabolites during tomato fruit ripening. In the future, we need to further understand the molecular mechanism of melatonin in tomato fruit to lay a solid foundation for quality improvement breeding.

Studies on the diversity within and among cabbage (Brassica oleracea L. var. capitata L.), cauliflower (Brassica oleracea var. botrytis), and Chinese cabbage (Brassica rapa L. ssp. pekinensis) variants are essential for the development of healthy diets. However, most studies on them have been limited to a single species, with little integrated analysis between them. In this study, the diversity within and among these species and varieties is assessed by determining the contents of 15 major characteristic nutrients, antioxidants, and minerals in 12 varieties of cabbage, 9 varieties of cauliflower, and 12 varieties of Chinese cabbage cultivated under the same conditions. The results show that there are significant differences in the compositional distributions of cabbage, cauliflower, and Chinese cabbage. Cabbage has the highest contents of soluble sugars (27.73 mg·kg⁻¹ FW), flavonoids (5.90 mg·g⁻¹ FW), and Fe (46.90 mg·kg⁻¹ DW). Cauliflower is an ideal source of soluble protein (603.04 mg·kg⁻¹ FW), polyphenols (1.53 mg·g⁻¹ FW), glucosinolates (25.27 μmol·g⁻¹ FW), and Cu (4.25 mg·kg⁻¹ DW). Chinese cabbage is rich in vitamin C (0.45 mg·g⁻¹ FW) and minerals (K, Ca, Mg, P, Mn, and Zn, at 9206.67 mg·kg⁻¹ DW, 3297.00 mg·kg⁻¹ DW, 3322.79 mg·kg⁻¹ DW, 5614.78 mg·kg⁻¹ DW, 15.36 mg·kg⁻¹ DW, and 21.87 mg·kg⁻¹ DW, respectively). There is a correlation between the quality, antioxidant properties, and minerals of the three species. In principal component analysis, a wide distribution of cabbage varieties and a high degree of overlap with the confidence ellipse of cauliflower are observed, indicating that certain cabbage varieties share compositional characteristics with cauliflower. These findings provide a reference for selecting varieties with higher nutritional value and antioxidant properties, as well as breeding new varieties.

The biological activities of the primary metabolites and secondary metabolites of 69 green cabbage varieties were tested. The LC-MS detection method was used to determine the content of 19 free amino acids (lysine, tryptophan, phenylalanine, methionine, threonine, isoleucine, leucine, valine, arginine, asparagine, glycine, proline, tyrosine, glutamine, alanine, aspartic acid, serine, and glutamate). The content of 10 polyphenols (chlorogenic acid, gallic acid, 4-coumaric acid, ferulic acid, gentisic acid, cymarin, erucic acid, benzoic acid, rutin, and kaempferol) was determined by the HPLC detection method. Considering the complexity of the data obtained, variance analysis, diversity analysis, correlation analysis, hierarchical cluster analysis (HCA), and principal component analysis (PCA) were used to process and correlate amino acid or polyphenol data, respectively. The results showed that there were significant differences between the different amino acids and polyphenols of the 69 cabbage varieties. The most abundant amino acids and polyphenols were Glu and rutin, respectively. Both amino acids and polyphenols had a high genetic diversity, and multiple groups of significant or extremely significant correlations. The 69 cabbage varieties were divided into two groups, according to 19 amino acid indexes, by PCA. Among them, seven varieties with high amino acid content all fell into the fourth quadrant. The HCA of amino acids also supports this view. Based on 10 polyphenols, the 69 cabbage varieties were divided into two groups by HCA. Based on 29 indexes of amino acids and polyphenols, 69 cabbage varieties were evaluated and ranked by PCA. Therefore, in this study, cabbage varieties were classified in accordance with the level of amino acids and polyphenols, which provided a theoretical basis for the genetic improvement of nutritional quality in cabbage.

Supplementary light exposure using light-emitting diodes (LEDs) promotes the growth of tomato plants in greenhouses. Owing to the biological clock in plants, determining the period during which they must be exposed to supplementary light is essential to enhance growth. In this study, we used red and blue LEDs (red:blue = 7:2) as the supplementary light source, to determine the effects of different light supplemental periods on the growth and photosynthetic characteristics of tomato seedlings. Light supplementation in the morning and evening promoted the growth of tomato plants to varying degrees, including the accumulation of photosynthetic products in the leaves. Light supplementation in the morning enhanced dry matter accumulation, root growth, and the contents of chlorophyll and carotenoids in the leaves. Although both morning and evening light supplementation increased the levels of gas exchange parameters and Rubisco activity in tomato leaves, these effects were more prominent after morning light supplementation. Furthermore, red and blue light supplementation in the morning pre-activated the key photosynthetic enzymes, promoted the synthesis and accumulation of photosynthetic pigments, increased the photosynthetic capacity of, and photosynthate production in, tomato leaves. These findings suggest that light supplementation in the morning is more effective in promoting the growth and development of tomato plants cultivated in greenhouses.

Hydrogen sulfide (H₂S) is involved in the regulation of plant salt stress as a potential signaling molecule. This work investigated the effect of H₂S on cucumber growth, photosynthesis, antioxidation, ion balance, and other salt tolerance pathways. The plant height, stem diameter, leaf area and photosynthesis of cucumber seedlings were significantly inhibited by 50 mmol·L⁻¹ NaCl. Moreover, NaCl treatment induced superoxide anion (O₂^·−) and Na⁺ accumulation and affected the absorption of other mineral ions. On the contrary, exogenous spraying of 200 μmol·L⁻¹ sodium hydrosulfide (NaHS) maintained the growth of cucumber seedlings, increased photosynthesis, enhanced the ascorbate–glutathione cycle (AsA–GSH), and promoted the absorption of mineral ions under salt stress. Meanwhile, NaHS upregulated SOS1, SOS2, SOS3, NHX1, and AKT1 genes to maintain Na⁺/K⁺ balance and increased the relative expression of MAPK3, MAPK4, MAPK6, and MAPK9 genes to enhance salt tolerance. These positive effects of H₂S could be reversed by 150 mmol·L⁻¹ propargylglycine (PAG, a specific inhibitor of H₂S biosynthesis). These results indicated that H₂S could mitigate salt damage in cucumber, mainly by improving photosynthesis, enhancing the AsA–GSH cycle, reducing the Na⁺/K⁺ ratio, and inducing the SOS pathway and MAPK pathway.