Salt stress poses a serious threat to tomato production. Red to far-red light ratio (R/FR) is actively involved in the regulation of tomato growth and development; however, it is still uncertain whether and how R/FR improves fruit quality under salt stress. Thus, we conducted metabolomic analysis of tomato fruits under four treatments, including R/FR = 7 (CK), R/FR = 0.7 (L), R/FR = 7 and 100 mmol·L⁻¹ NaCl (Na), and R/FR = 0.7 and 100 mmol·L⁻¹ NaCl (Na+L). Metabolomic analysis indicated that both low R/FR and salt stress enhanced organic acids and phenols accumulation; however, additional low R/FR mainly improved carbohydrates, organic acids, phenols and amino acids accumulation in salt-stressed tomato fruit. Physiological studies were consistent with the above results and further revealed that additional low R/FR drastically promoted plant growth, soluble sugar, total phenol and flavonoid contents, improved osmotic pressure balance and antioxidant capacity, and notably relieved the salt stress-induced suppressions. This study proved the importance of applying light quality regulation in salt-resistant tomato production.

Due to its sensitivity to cold temperatures, cucumber growth is substantially constrained by suboptimal temperature stress in northern China’s off-season production systems. Suboptimal temperatures severely repress the nutrient absorption, growth, and yield formation of vegetables in solar greenhouses during winter and early spring in China. Alginate oligosaccharides (AOSs) are anionic acidic polysaccharides derived from brown algae, known for promoting plant growth and alleviating abiotic stress. In this study, we aimed to investigate the effects of different nutrient solution concentrations combined with AOS on the growth and nutrient uptake of cucumber seedlings under suboptimal temperatures (15/8 °C, day/night). Potted ‘Jinchun 4’ cucumber seedlings grown in coconut coir were treated with 0.5×, 1.0×, or 1.5× strength of Hoagland solution alone (N0.5, N1, N1.5), or with 30 mg·L⁻¹ AOS (A0.5, A1, A1.5). The results showed that the growth attributes and nitrogen (N) accumulation of cucumber plants of N1 and N1.5 were significantly higher than those of N0.5. Additionally, plants of A0.5 exhibited significantly higher plant height, chlorophyll a content, root surface area, root volume, root vitality, N metabolism enzyme (NR, GDH, GS) activities, and N accumulation, than those under N0.5, N1, or N1.5. Moreover, compared to A0.5, the net photosynthetic rate, total root length, root surface area, root N content, leaf nitrate reductase activity, root glutamate dehydrogenase activity, and N accumulation of A1 and A1.5 were significantly higher than those of A0.5. Correlation analysis revealed strong linkages between root morphology traits and tissue N content. In summary, under suboptimal temperature conditions, the application of AOS improved cucumber seedlings’ nutrient absorption and growth more efficiently than merely raising nutrient levels, as it enhanced root surface area, root vitality, and N metabolic enzyme activities.

Alginate oligosaccharides (AOSs) have been shown to be effective in enhancing crop growth. However, their functions in horticulture crops and growth-promoting mechanisms remain insufficiently characterized. This study employed pot cultivation experiments to investigate the effects of AOS root drenching (0, 15, 30, 45 mg·L⁻¹) on tomato (Solanum lycopersicum L.) seedling growth, photosynthetic performance, and phytohormone accumulation. The results showed that AOS promoted the leaf count per plant, leaf area of the youngest fully expanded leaves, shoot and root dry mass, chloroplast pigment contents and photosynthetic rate of tomato seedlings. And the 30 mg·L⁻¹ treatment consistently showed optimal efficacy, in which tomato seedlings also exhibited a significantly longer total root length, a larger root surface area and a greater number of root tips compared to the control. Phytohormone profiling revealed that AOS differentially regulated shoot/root phytohormones as follows: increasing auxins/cytokinins (CKs)/GA₁₉ content in shoots and Indole-3-acetic acid (IAA)/CKs/1-aminocyclopropane-1-carboxylic acid (ACC) content in roots, while decreasing root Jasmonic acid (JA)/5-deoxystrigol (5DS) contents. Finally, these findings demonstrate that AOS enhances tomato growth by coordinately reprogramming phytohormone homeostasis.

Tomato seedlings were treated with nutrient solutions containing varying nitrogen concentrations (50, 150, and 250 mg·L⁻¹) after germination until the completion of flower bud differentiation. The changes in nutrient content, enzyme activity, endogenous hormone levels, and gene expression in the stem apex were analyzed to explore the mechanisms regulating the number of locules in tomatoes at different nitrogen concentrations. The results indicated that an increase in nitrogen concentration facilitated the differentiation of tomato flower buds, increased the number of fruit locules, and increased the contents of soluble sugar, soluble protein, starch, and sucrose, as well as the activities of the enzymes POD, NR, and PPO in the seedling stem apex. The contents of soluble sugars and soluble proteins, as well as the activities of POD, NR, and PPO, were closely correlated with the number of fruit locules. An increase in nitrogen concentration was also found to elevate cytokinin levels while reducing auxin content in the stem apex. The transcriptome analysis screened for peroxidase genes, auxin response genes, and cytokinin synthesis genes. The analysis of gene expression patterns suggests that CKX and LOG6 play significant roles in flower development. Additionally, combined physiological changes indicated that an increase in nitrogen concentration during the tomato seedling stage leads to a higher number of fruit locules, which may be associated with elevated cytokinin content, primarily involving the key genes CKX and LOG6.

Fruit locule number is an important agronomic trait that affects fruit appearance, quality, and yield. CLAVATA3 (SlCLV3) is a candidate gene of the fasciated (fas) locus that plays a role in controlling the number of flower organs and fruit locules in tomato. The SlCLV3 encoding signal peptide mainly acts by inhibiting the expression of WUSCHEL (WUS) but there is little research about how the receptor transmits the CLV3 signal to WUS and inhibits its expression. The CRISPR/Cas9 method was employed to edit the first exon of tomato SlCLV3 in this study, leading to the functional deletion of SlCLV3. As a result, flowers with a high number of organs and fruits with a high number of locules were produced. We screened six candidate genes using the transcriptome of clv3 mutants, analyzed expression variations in these genes between the cultivated allele and wild-type allele of fas, and showed that only SlLET6 and SlGIF1 (GRF1-interacting factor 1) were influenced by the fas locus. SlLET6 overexpression resulted in an increase in flower carpels and fruit locules. These results suggest that SlLET6 may be the downstream gene of SlCLV3 regulating the number of carpels and fruit locules in tomato.