Background: Tomato is one of the most popular vegetables, and middle tolerance for salt stress. Spermidine (Spd) has an important role in plant defense mechanisms against abiotic stress; however, relatively few data are available regarding Spd in responses of tomato to saline-alkaline stress. The effect of 0.25 mmol/L Spd on some physiological parameters of two tomato cultivars grown in 75 mmol/L saline-alkaline solutions were studied. Two cultivars are cv. Jinpeng chaoguan which is a highly salt-tolerant ecotype and cv. Zhongza No. 9 which is more salt-sensitive ecotype. Results: Saline-alkaline stress upset nitrogen metabolism, induced the antioxidant enzyme activities, and accumulated much more reactive oxygen species (ROS) and osmoregulation substances in two tomato cultivars leaves. Under saline-alkaline stress condition, Spd-treated seedlings accumulated more osmoregulation substances and had greater activities of antioxidative enzymes. Exogenous Spd counteracted the stress-induced increase of contents of malondialdehyde and ammonium, glutamate dehydrogenase activity, and decreased in nitrate, nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, glutamate oxaloacetate transaminase, and glutamate pyruvate transaminase activities. Additionally, the effect of Spd was more significantly in salt-sensitive cultivar ‘Zhongza No. 9’. Conclusions: Overall, exogenous spermidine can attenuate negative effects of saline-alkaline stress on tomato seedlings which effects may depend on the plant species, and even cultivars.

Bacillus subtilis was applied in peat-based soilless cultivation systems containing a mixed substrate (peat:vermiculite:perlite = 2:1:1, v/v/v) and irrigated by one-strength or four-strength Hoagland’s nutrient solution to explore whether it can alleviate inhibition by higher-nutrient solutions (four-strength) and bring benefits to improvements of quality. The results showed that higher-nutrient solutions improved the flavor quality of cucumber fruit; especially, the contents of (E,Z)-2,6-nonadienal and (E)-2-Nonenal were effectively increased, which are the special flavor substances of cucumber. B. subtilis K424 effectively improved growth performance, photosynthetic capacity, vitamin C content, soluble sugars, soluble protein, and total pectin in cucumber under higher nutrition solution conditions. Compared with the higher solution treatment, the bacterial diversity significantly increased, whereas the presence of fungi had no significant difference following the B. subtilis K424 application. Moreover, B. subtilis K424 reduced the relative abundance of Actinomadura and promoted that of the Rhodanobacter, Bacillus, Pseudomonas, Devosiaceae, and Blastobotrys genera. Redundancy analysis showed that Bacillus, Rhodanobacter, and Blastobotrys were positively correlated with the substrate enzyme of sucrase, catalase, and urease. This study provides insight that B. subtilis K424 mitigated the deleterious effects of high levels of nutrition solution on cucumber growth and quality by improving the substrate enzyme, regulating the microbial community structure, and enhancing the photosynthetic capacity.

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.

Iron (Fe) deficiency is a common abiotic stress in plants grown in alkaline soil that causes leaf chlorosis and affects root development due to low plant-available Fe concentration. Silicon (Si) is a beneficial element for plant growth and can also improve plant tolerance to abiotic stress. However, the effect of Si and regulatory mechanisms on tomato plant growth under Fe deficiency remain largely unclear. Here, we examined the effect of Si application on the photosynthetic capacity, antioxidant defense, sugar metabolism, and organic acid contents under Fe deficiency in tomato plants. The results showed that Si application promoted plant growth by increasing photosynthetic capacity, strengthening antioxidant defense, and reprogramming sugar metabolism. Transcriptomics analysis (RNA-seq) showed that Si application under Fe deficiency up-regulated the expression of genes related to antioxidant defense, carbohydrate metabolism and organic acid synthesis. In addition, Si application under Fe deficiency increased Fe distribution to leaves and roots. Combined with physiological assessment and molecular analysis, these findings suggest that Si application can effectively increase plant tolerance to low Fe stress and thus can be implicated in agronomic management of Fe deficiency for sustainable crop production. Moreover, these findings provide important information for further exploring the genes and underlying regulatory mechanisms of Si-mediated low Fe stress tolerance in crop plants.

Chinese cabbage is a vital while perishable leafy vegetable. Blue-green light combined treatment was found to be better to retain high nutritional value in Chinese cabbage than blue or green monochromatic light treatments by increasing the contents of soluble protein, indol-3-ylmethyl (I3M), flavonoids, total phenols and carotene. Gene expression study further revealed that blue-green light treatment increased the expression of biosynthetic genes in the metabolic pathways of glucosinolates (BrCYP79B2, BrIGMT1), flavonoids (BrCHS.1, BrF3H, BrCHI) and carotenoids (BrPSY1, BrLCYB, BrLCYE, BrVDE), as well as the light signal master regulator gene BrHY5.2. In addition, the blue-green light treatment up-regulated the activities of antioxidant enzymes, as well as 2,2-diphenyl-1-picrylhydrazyl and ferric-reducing antioxidant power activities, while reducing the levels of superoxide anion, hydrogen peroxide (H₂O₂), polyphenol oxidase (PPO) activity and malondialdehyde (MDA). Overall, our findings confirmed that blue-green light treatment can effectively enrich the nutritional value and prolong the shelf life of Chinese cabbage.