To investigate the effects of exogenous spermidine (Spd) on metabolism changes under salt stress in cucumber roots, a gas chromatography-mass spectrometry (GC-MS) was performed. The results showed that most of the 142 metabolites responded to salt stress or exogenous Spd treatment. Salt stress reduced carbon consumption, resulted in the transformation of glycolysis and the tricarboxylic acid (TCA) cycle to the pentose phosphate pathway (PPP), and meanwhile increased salicylic acid (SA) and ethylene synthesis, and, thus, inhibited the growth of seedlings. However, exogenous Spd further improved the utilization of carbon, the energy-saving pattern of amino acid accumulation, and the control of hydroxyl radicals. In conclusion, Spd could promote energy metabolism and inhibit SA and ethylene synthesis in favor of root growth that contributes to higher salt tolerance. This study provides insight that may facilitate a better understanding of the salt resistance by Spd in cucumber seedlings.

Essential macronutrient nitrogen (N) is crucial for plant growth and yield, but excessive chemical N fertilizer not only increases unnecessary production costs but also causes environmental pollution. Therefore, reducing N fertilizer use by increasing organic fertilizer use is crucial for sustainable agriculture. In this study, we investigated the effects of three nitrogen levels—the recommended rate (N), a 20.0% reduced rate (0.8N), and a 40.0% reduced rate (0.6N)—and two levels of organic fertilizer—a normal dose (M) and a four-times the normal dose (4M)—combined with root application of the beneficial element silicon (Si) on the photosynthetic characteristics, yield, and fruit quality of the tomato cultivar ‘Tianxi No. 5’. Compared with M + N treatment, the longitudinal diameter, transverse diameter, fruit weight, and fruit yield of tomato fruit in 4M + 0.6N treatment significantly increased by 12.4%, 14.6%, 14.5%, and 12.8%, respectively, while the yield was further improved with Si application. In addition, a reduction in N fertilizer and an increase in organic fertilizer, combined with Si application, improved fruit quality parameters such as concentrations of vitamin C, lycopene, phenols, flavonoids, sucrose, fructose, etc., and promoted sugar metabolism-related enzyme activity (sucrose synthase, invertase, and sucrose phosphate synthase) and the accumulation of N in the fruit. The principal component analysis and three-factor analysis of variance (ANOVA) of the fruit quality and yield indices showed that nitrogen fertilizer, organic fertilizer, silicon fertilizer, and the interaction of the three had significant effects on the quality and yield of tomato fruits, and that the 4M + 0.6N + Si treatment had the best combined effect on the yield and quality of the tomatoes. Thus, a moderate reduction in chemical N fertilizer, combined with increased organic fertilizer and Si, could be an effective agronomic practice for improving the yield and quality of tomatoes.

Glucosinolates (GSLs) are important secondary metabolites that play important defensive roles in cruciferous plants. Chinese flowering cabbage, one of the most common vegetable crops, is rich in GSLs and thus has the potential to reduce the risk of cancer in humans. Many genes that are involved in GSL biosynthesis and metabolism have been identified in the model plant Arabidopsis thaliana; however, few studies investigated the genes related to GSL biosynthesis and metabolism in Chinese flowering cabbage. In the present study, the GSL composition and content in three different organs of Chinese flowering cabbage (leaf, stalk, and flower bud) were determined. Our results showed that the total GSL content in flower buds was significantly higher than in stalks and leaves, and aliphatic GSLs were the most abundant GSL type. To understand the molecular mechanisms underlying the variations of GSL content, we analyzed the expression of genes encoding enzymes involved in GSL biosynthesis and transport in different tissues of Chinese flowering cabbage using RNA sequencing; the expression levels of most genes were found to be consistent with the pattern of total GSL content. Correlation and consistency analysis of differentially expressed genes from different organs with the GSL content revealed that seven genes (Bra029966, Bra012640, Bra016787, Bra011761, Bra006830, Bra011759, and Bra029248) were positively correlated with GSL content. These findings provide a molecular basis for further elucidating GSL biosynthesis and transport in Chinese flowering cabbage.

Eceriferum (cer) genes are a group of genes that have functions in wax biosynthesis, which play important roles in plant epidermal permeability, drought resistance, fertility, and organ fusion. In this study, CsCER4, an AtCER4 homologue, was cloned from cucumber (Cucumis sativus L.). The full-length cDNA of CsCER4 is 1464 bp, encoding a protein with 487 amino acid residues. CsCER4 was expressed in all analysed tissues, including leaves, male flowers, female flowers, and fruit. Its expression level among fruit development increased and then decreased, and the expression was markedly different between 3413 (glossy type cucumber) and 3401 (waxy type cucumber), suggesting that CsCER4 has a role in wax biosynthesis.

Environmental stress, notably the exposure to low temperatures during the early developmental stages of seedlings, has been identified as a critical determinant impacting the yield and quality of tomato crops cultivated in greenhouses. Silicon (Si), recognized as a beneficial element, is posited to mitigate the adverse effects of such stress on plant physiology. This study explores whether exogenous Si fertilizer can effectively alleviate the stress of low temperature and cold damage on tomato plant growth, fruit yield, and quality. Tomato plants were placed under low temperature conditions (6 °C at night, daily average temperature 15 °C), with normal temperature conditions as the control (below 16 °C at night, daily average temperature 28 °C), and two different concentrations of nano Si and ionic Si (50 mg·L⁻¹ and 200 mg·L⁻¹) were sprayed on the leaves, with an equivalent amount of deionized water as the control, for a total of 10 treatments. Relevant indexes were measured to investigate the effects of exogenous Si on tomato resistance, yield, and quality under low-temperature stress. The results show that compared with the control treatment, the plant height, stem diameter, and fresh weight of above-ground and underground parts of tomato seedlings decreased significantly by 46.52%, 42.53%, 28.81%, and 28.97%, respectively, after 15 days of low-temperature stress (p < 0.05), and in order to resist low temperature, the activity of antioxidant enzymes and the content of osmotic adjustment substances were up-regulated in seedlings. Ultimately, low-temperature stress inhibited the morphological growth, nutritional quality, and yield of fruits. Both concentrations of Si application can promote the growth and biomass accumulation of tomato plants under low temperature conditions. Moreover, it significantly ameliorated the osmotic adjustment and antioxidant capacity of the plants, thereby alleviating the low-temperature stress. Under low-temperature stress, 50 mg L⁻¹ ionic Si was the most effective for increasing tomato yield per plant, which was significantly increased by 22.44% compared with the control treatment (p < 0.05). Consequently, the study advocates for the application of 50 mg·L⁻¹ ionic Si fertilizer as a strategy to mitigate the impact of low-temperature stress on tomato plants. Furthermore, the use of nano Si fertilizer has been demonstrated to exert a significant influence on enhancing both the yield and quality of tomatoes, with a 50 mg·L⁻¹ concentration of nano Si fertilizer leading to a notable increase in yield by 20.15% under normal temperature conditions (p < 0.05). These findings are intended to furnish a theoretical foundation and practical direction for advancing research aimed at combating the detrimental effects of low-temperature stress in the context of protected vegetable cultivation.

Carrot is an important vegetable with roots as the edible organ. A complex regulatory network controls root growth, in which auxin is one of the key players. To clarify the molecular mechanism on auxin regulating carrot root expansion, the growth process and the indole-3-acetic acid (IAA) content in the roots were measured in this experiment. It was found that the rapid expansion period of the root was from 34 to 41 days after sowing and the IAA content was the highest during this period. The root growth then slowed down and the IAA levels decreased. Using the transcriptome sequencing database, we analyzed the expression of IAA-metabolism-related genes and found that the expression of most of the IAA synthesis genes, catabolism genes, and genes related to signal transduction was consistent with the changes in IAA content during root expansion. Among them, a total of 31 differentially expressed genes (DEGs) were identified, including 10 IAA synthesis genes, 8 degradation genes, and 13 genes related to signal transduction. Analysis of the correlations between the DEGs and IAA levels showed that the following genes were closely related to root development: three synthesis genes, YUCCA10 (DCAR_012429), TAR2 (DCAR_026162), and AMI1 (DCAR_003244); two degradation genes, LPD1 (DCAR_023341) and AACT1 (DCAR_010070); and five genes related to signal transduction, IAA22 (DCAR_012516), IAA13 (DCAR_012591), IAA27 (DCAR_023070), IAA14 (DCAR_027269), and IAA7 (DCAR_030713). These results provide a reference for future studies on the mechanism of root expansion in carrots.