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.

Suboptimal temperatures severely repress the nutrient absorption, growth, and yield formation of vegetables in solar greenhouse during winter and early spring in China. Alginate oligosaccharides (AOS) 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 concentration combined with AOS on the growth and nutrient uptake of cucumber seedling under suboptimal temperatures (15/8 °C, day/night). Potted ‘Jinchun No. 4’ cucumber seedlings grown in coconut coir were treated with 0.5×, 1.0×, or 1.5× strength of Hogland solution alone (N0.5, N1, N1.5), or with 30 mg·L⁻¹ AOS (A0.5, A1, A1.5). The results showed that growth attributes, and nitrogen accumulation of cucumber plants of N1 and N1.5 were significantly higher than those of N0.5. And plants of A0.5 exhibited significantly higher plant height, chlorophyll a content, root surface area, root volume, root vitality, nitrogen 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 indicated strong positive relationships between root surface area, root volume, root vitality, and N content in plant organs. In summary, AOS enhanced the nutrient uptake and growth of cucumber seedlings through promoting root surface area, root vitality, and nitrogen metabolism enzyme activities under suboptimal temperatures conditions, therefor it has a good application prospect and great ecological value for increasing nutrient use efficiency and reducing the use of chemical fertilizers.

Locule number, a key agronomic trait determining tomato yield and quality, is regulated by genetic determinants, low temperature, and nitrogen supply, and is also affected by phosphorus concentration during the seedling stage, although the underlying mechanism remains unclear. To address this, we treated ‘Mati’ tomato with three phosphorus concentrations (high, normal, and low) and systematically analyzed the physiological and molecular changes associated with locule formation. Results showed that high-P treatment significantly increased floral organ and locule number, increased the content of sucrose, soluble sugars, reducing sugars, fructose, soluble protein, and starch in the shoot apex, enhanced POD and APX activities, inhibited SOD activity, reduced O₂⁻ content, increased MDA content, and promoted the accumulation of active auxin and cytokinin. Based on RT-qPCR validation and their known roles in sucrose metabolism and signaling, we identified PMEI (a putative invertase/pectin methylesterase inhibitor) and TPS.1 (a trehalose-6-phosphate synthase) as candidate genes, with PMEI being upregulated and TPS.1 downregulated under high-P treatment. Consistently, TPS enzyme activity in the shoot apex was also significantly reduced under high-P treatment. In locule number mutants, their expression levels showed positive and negative correlations with locule number, respectively. These results suggest that PMEI and TPS.1 may participate in phosphorus-regulated locule number formation through coordinated modulation of sucrose accumulation and signaling in the shoot apex.