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Nitrogen (N) is a major limiting factor for plant growth and vegetable production. Understanding the regulatory mechanisms of N uptake, transport, and assimilation is key to improving N use efficiency in plants. Ammonium transporters (AMTs) play an important role in plant N metabolism. In this study, we isolated an important AMT1 subfamily member (BcAMT1;5) with a highly conserved signatural AMT1 subfamily motif from flowering Chinese cabbage. Based on functional complementation in yeast mutant 31019b and overexpression of BcAMT1;5 in Arabidopsis, BcAMT1;5 is a functional AMT. Tissue expression analysis showed that BcAMT1;5 was mainly expressed in roots and showed multiple N regime transcript patterns to respond to varying nutritional conditions. This was up-regulated by N-deficiency and down-regulated by supplying NH4+. The glucuronidase (GUS) activities of BcAMT1;5pro::GUS showed a similar change in response to different N conditions. Overexpression of BcAMT1;5 accelerated the growth of transgenic seedlings, increased NH4+ net influxes, and enhanced the content and accumulation of NH4+ and NO3− at low N concentrations. Additionally, it increased the transcript levels of N assimilation-related genes in shoots. These results indicate that BcAMT1;5 may participate in N uptake and assimilation under various N conditions in flowering Chinese cabbage, but it was differed obviously from other AMT1s. [ABSTRACT FROM AUTHOR]

Compared with sole nitrogen (N), the nutrition mixture of ammonium (NH4+) and nitrate (NO3–) is known to better improve crop yield and quality. However, the mechanism underlying this improvement remains unclear. In the present study, we analyzed the changes in nutrient solution composition, content of different N forms in plant tissues and exudates, and expression of plasma membrane (PM) H+-ATPase genes (HAs) under different NH4+/NO3– ratios (0/100, 10/90, 25/75, 50/50 as control, T1, T2, and T3) in flowering Chinese cabbage. We observed that compared with the control, T1 and T2 increased the economical yield of flowering Chinese cabbage by 1.26- and 1.54-fold, respectively, whereas T3 significantly reduced plant yield. Compared with the control, T1–T3 significantly reduced the NO3– content and increased the NH4+, amino acid, and soluble protein contents of flowering Chinese cabbage to varying extents. T2 significantly increased the N use efficiency (NUE), whereas T3 significantly decreased it to only being 70.25% of that of the control. Owing to the difference in N absorption and utilization among seedlings, the pH value of the nutrient solution differed under different NH4+/NO3– ratios. At harvest, the pH value of T2 was 5.8; in the control and T1, it was approximately 8.0, and in T3 it was only 3.6. We speculated that appropriate NH4+/NO3– ratios may improve N absorption and assimilation and thus promote the growth of flowering Chinese cabbage, owing to the suitable pH value. On the contrary, addition of excessive NH4+ may induce rhizosphere acidification and ammonia toxicity, causing plant growth inhibition. We further analyzed the transcription of PM H+-ATPase genes (HAs). HA1 and HA7 transcription in roots was significantly down-regulated by the addition of the mixture of NH4+ and NO3–, whereas the transcription of HA2 , HA9 in roots and HA7 , HA8 , and HA10 in leaves was sharply up-regulated by the addition of the mixture; the transcription of HA3 was mainly enhanced by the highest ratio of NH4+/NO3–. Our results provide valuable information about the effects of treatments with different NH4+/NO3– ratios on plant growth and N uptake and utilization. [ABSTRACT FROM AUTHOR]

Plant growth and development are tightly regulated by phytohormones. However, little is known about the interaction between auxin and gibberellin acid (GA) during flower stalk elongation and how it is directly related to organ formation. Therefore, the effects of indole acetic acid (IAA) and GA3 treatments and their interaction on flower stalk elongation in flowering Chinese cabbage were investigated. The growth of flowering Chinese cabbage is regulated by IAA and GA3, and the opposite results were observed after treatments with uniconazole (GA synthesis inhibitor) and N-1-naphthylphthalamic acid (NPA) (auxin transport inhibitor). Anatomical analysis of the pith region in stalks revealed that IAA promoted expansion via signal transduction and transport pathways. GA3 regulated the elongation of flower stalks by controlling GA synthesis and partially controlling the IAA signaling pathway. GA3 also had a stronger effect on stalk elongation than IAA. The results of qRT-PCR and histological analysis revealed that GA3 and IAA induced the expansion of cell walls by activating the expression of genes encoding cell wall structural proteins such as Expansin (EXP). These findings provide new insights into the mechanism of stalk formation regulated by the combination of IAA and GA3. [ABSTRACT FROM AUTHOR]

The provision of ammonium (NH4+) and nitrate (NO3−) mixture increases the total nitrogen (N) than the supply of sole NH4+ or NO3– with the same concentration of total N; thus, the mixture contributes to better growth in Brassica campestris. However, the underlying mechanisms remain unknown. In this study, we analyzed NH4+ and NO3– fluxes using a scanning ion-selective electrode technique to detect under different N forms and levels in B. campestris roots. We observed that the total N influxes with NH4+ and NO3− mixture were 1.25- and 3.53-fold higher than those with either sole NH4+ or NO3−. Furthermore, NH4+ and NO3– might interact with each other under coexistence. NO3– had a positive effect on net NH4+ influx, whereas NH4+ had a negative influence on net NO3– influx. The ammonium transporter (AMT) played a key role in NH4+ absorption and transport. Based on expression analysis, BcAMT1.2 differed from other BcAMT1s in being upregulated by NH4+ or NO3−. According to sequence analysis and functional complementation in yeast mutant 31019b, AMT1.2 from B. campestris may be a functional AMT. According to the expression pattern of BcAMT1.2 , β-glucuronidase activity, and the cellular location of its promoter, BcAMT1.2 may be responsible for NH4+ transport. Following the overexpression of BcAMT1.2 in Arabidopsis , BcAMT1.2 -overexpressing lines grew better than wildtype lines at low NH4+ concentration. In the mixture of NH4+ and NO3–, NH4+ influxes and NO3– effluxes were induced in BcAMT1.2 -overexpressing lines. Furthermore, transcripts of N assimilation genes (AtGLN1.2 , AtGLN2 , and AtGLT1) were significantly upregulated, in particular, AtGLN1.2 and AtGLT1 were increased by 2.85–8.88 times in roots, and AtGLN1.2 and AtGLN2 were increased by 2.67–4.61 times in leaves. Collectively, these results indicated that BcAMT1.2 may mediate in NH4+ fluxes under the coexistence of NH4+ and NO3– in B. campestris. [ABSTRACT FROM AUTHOR]

Flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) is an important and extensively cultivated vegetable in south China, and its stalk development is mainly regulated by gibberellin (GA). DELLA proteins negatively regulate GA signal transduction and may play an important role in determining bolting and flowering. Nevertheless, no systematic study of the DELLA gene family has been undertaken in flowering Chinese cabbage. In the present study, we found that the two-true-leaf spraying of gibberellin A3 (GA3) did not promote bolting but did promote flowering, whereas the three-true-leaf spraying of GA3 promoted both bolting and flowering. In addition, we identified five DELLA genes in flowering Chinese cabbage. All five proteins contained DELLA, VHYNP, VHIID, and SAW conserved domains. Protein-protein interaction results showed that in the presence of GA3, all five DELLA proteins interacted with BcGID1b (GA-INSENSITIVE DWARF 1b) but not with BcGID1a (GA-INSENSITIVE DWARF 1a) or BcGID1c (GA-INSENSITIVE DWARF 1c). Their expression analysis showed that the DELLA genes exhibited tissue-specific expression, and their reversible expression profiles responded to exogenous GA3 depending on the treatment stage. We also found that the DELLA genes showed distinct expression patterns in the two varieties of flowering Chinese cabbage. BcRGL1 may play a major role in the early bud differentiation process of different varieties, affecting bolting and flowering. Taken together, these results provide a theoretical basis for further dissecting the DELLA regulatory mechanism in the bolting and flowering of flowering Chinese cabbage. [ABSTRACT FROM AUTHOR]