Flowering Chinese cabbage is one of the most economically important stalk vegetables. However, the molecular mechanisms underlying bolting, which is directly related to stalk quality and yield, in this species remain unknown. Previously, we examined five key stem development stages in flowering Chinese cabbage. Here, we identified a gene, BcSOC1 (SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1), in flowering Chinese cabbage using transcriptome analysis, whose expression was positively correlated with bolting. Exogenous gibberellin (GA₃) and low-temperature treatments significantly upregulated BcSOC1 and promoted early bolting and flowering. Additionally, BcSOC1 overexpression accelerated early flowering and stem elongation in both Arabidopsis and flowering Chinese cabbage, whereas its knockdown dramatically delayed bolting and flowering and inhibited stem elongation in the latter; the inhibition of stem elongation was more notable than delayed flowering. BcSOC1 overexpression also induced cell expansion by upregulating genes encoding cell wall structural proteins, such as BcEXPA11 (cell wall structural proteins and enzymes) and BcXTH3 (xyloglucan endotransglycosidase/hydrolase), upon exogenous GA₃ and low-temperature treatments. Moreover, the length of pith cells was correlated with stem height, and BcSOC1 interacted with BcAGL6 (AGAMOUS-LIKE 6) and BcAGL24 (AGAMOUS-LIKE 24). Thus, BcSOC1 plays a vital role in bolting and stem elongation of flowering Chinese cabbage and may play a novel role in regulating stalk development, apart from the conserved function of Arabidopsis SOC1 in flowering alone.

Gibberellin (GA) plays a major role in controlling Brassica rapa stalk development. As an essential negative regulator of GA signal transduction, DELLA proteins may exert significant effects on stalk development. However, the regulatory mechanisms underlying this regulation remain unclear. In this study, we report highly efficient and inheritable mutagenesis using the CRISPR/Cas9 gene editing system in BraPDS (phytoene desaturase) and BraRGL1 (key DELLA protein) genes. We observed a loss-of-function mutation in BraRGL1 due to two amino acids in GRAS domain. The flower bud differentiation and bolting time of BraRGL1 mutants were significantly advanced. The expression of GA-regulatory protein (BraGASA6), flowering related genes (BraSOC1, BraLFY), expansion protein (BraEXPA11) and xyloglucan endotransferase (BraXTH3) genes was also significantly upregulated in these mutants. BraRGL1-overexpressing plants displayed the contrasting phenotypes. BraRGL1 mutants were more sensitive to GA signaling. BraRGL1 interacted with BraSOC1, and the interaction intensity decreased after GA₃ treatment. In addition, BraRGL1 inhibited the transcription-activation ability of BraSOC1 for BraXTH3 and BraLFY genes, but the presence of GA₃ enhanced the activation ability of BraSOC1, suggesting that the BraRGL1-BraSOC1 module regulates bolting and flowering of B. rapa through GA signal transduction. Thus, we hypothesized that BraRGL1 is degraded, and BraSOC1 is released in the presence of GA₃, which promotes the expression of BraXTH3 and BraLFY, thereby inducing stalk development in B. rapa. Further, the BraRGL1-M mutant promoted the flower bud differentiation without affecting the stalk quality. Thus, BraRGL1 can serve as a valuable target for the molecular breeding of early maturing varieties.

Flowering Chinese cabbage (Brassica campestris L. ssp. Chinensis var. utilis Tsen et Lee) is an important and extensively cultivated vegetable in south China, whose major food product is the stalk. In the process of stalk formation, its initiation and development are regulated by a series of hormonal signals, such as cytokinin and gibberellin. In this study, we analyzed the effects of zeatin (ZT) and gibberellin A3 (GA3), and their interaction, on the bolting of flowering Chinese cabbage. The results indicated that the three-true-leaf spraying of ZT and GA synthesis inhibitor (PAC) inhibited plant height but increased stem diameter. Cytokinin (CTK) synthesis inhibitor (YZJ) and GA3 treatment increased plant height and decreased stem diameter. In addition, ZT and GA3 co-treated plants displayed antagonistic effect. Further, 19 type-B authentic response regulators (ARR-Bs), the positive regulators of cytokinin signal transduction were identified from flowering Chinese cabbage. Comprehensive analysis of phylogeny showed BcARR-Bs clustered into three subfamilies with 10 conserved motifs. Analysis of their expression patterns in different tissues and at various growth stage, and their response to hormone treatment suggest that ARR1-b localized in the nucleus displayed unique highest expression patterns in stem tips, are responsive both to ZT and GA, suggesting a significant role in mediating the crosstalk of ZT and GA in the bolting of flowering Chinese cabbage.

The aim of this study was to determine the effects of various NH₄⁺/NO₃⁻ ratios in a nutrient solution on the growth and nitrogen uptake of Chinese kale under hydroponic conditions. The four NH₄⁺/NO₃⁻ ratios in the nutrient solution were CK (0/100), T1 (10/90), T2 (25/75), and T3 (50/50). An appropriate NH₄⁺/NO₃⁻ ratio (10/90, 25/75) promoted the growth of Chinese kale. T2 produced the highest fresh and dry weight among treatments, and all indices of seedling root growth were the highest under T2. A high NH₄⁺/NO₃⁻ ratio (50/50) promoted the growth of Chinese kale seedlings at the early stage but inhibited growth at the late growth stage. At harvest, the nutrient solution showed acidity. The pH value was the lowest in T3, whereas NH₄⁺ and NH₄⁺/NO₃⁻ ratios were the highest, which caused ammonium toxicity. Total N accumulation and N use efficiency were the highest in T2, and total N accumulation was the lowest in T3. Principal component analysis showed that T2 considerably promoted growth and N absorption of Chinese kale, whereas T3 had a remarkable effect on the pH value. These findings suggest that an appropriate increase in NH₄⁺ promotes the growth and nutrient uptake of Chinese kale by maintaining the pH value and NH₄⁺/NO₃⁻ ratios of the nutrient solution, whereas excessive addition of NH₄⁺ may induce rhizosphere acidification and ammonia toxicity, inhibiting plant growth.

Flowering Chinese cabbage (Brassica campestris L. ssp. Chinensis var. utilis Tsen et Lee) is a widely consumed vegetable in southern China with significant economic value. Developing product organs in the flowering Chinese cabbage involves two key processes: bolting and flowering. Nuclear factor Y (NF-Y) is a heterotrimeric transcription factor known for its crucial role in various plant developmental processes. However, there is limited information available on the involvement of this gene family during flowering during Chinese cabbage development. In this study, 49 BcNF-Y genes were identified and characterized along with their physicochemical properties, gene structure, chromosomal location, collinearity, and expression patterns. We also conducted subcellular localization, yeast two-hybrid, and transcriptional activity assays on selected BcNF-Y genes. The findings of this study revealed enhanced expression levels of specific BcNF-Y genes during the stalk development and flowering stages in flowering Chinese cabbage. Notably, BcNF-YA8, BcNF-YB14, BcNF-YB20, and BcNF-YC5 interacted with BcRGA1, a negative regulator of GA signaling, indicating their potential involvement in GA-mediated stalk development. This study provides valuable insights into the role of BcNF-Y genes in flowering Chinese cabbage development and suggests that they are potential candidates for further investigating the key regulators of cabbage bolting and flowering.

Nitrogen concentration affects growth and bolting of plants, but its regulation mechanism is still unclear. In this work, three nitrate concentration treatments (5%, 100%, 200%) in nutrient solution were conducted to explore the internal relationship between nitrogen and bolting in flowering Chinese cabbage. The results showed that the bolting and flowering time was earlier under the treatment with low nitrate and, the lower the nitrate concentration, the earlier the bolting and flowering. Low-nitrate treatment reduced the content of nitrate, soluble protein, free amino acid and total nitrogen, and increased the C/N ratio. The C/N ratio was significantly negatively correlated with plant height, stem thickness and biomass, while it was significantly positively correlated with flowering rate. Thus, it was indicated that nitrogen may affect bolting and flowering by regulating the C/N ratio of flowering Chinese cabbage plants. The expression of flowering-related genes (SOC1, LFY) was increased significantly under low nitrate treatment. In addition, the pith cell area at the stem tip was significantly reduced under low nitrate treatment, resulting in a significant decrease in stem thickness. The expression of cyclin- and expansin-related genes (CYCD3-3, CYCB1-1 and EXPA8) was significantly reduced, which indicated that nitrogen may regulate the stem development of flowering Chinese cabbage by regulating the expression of cyclin- and expansin-related genes.