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Nitrogen is the primary nutrient for plants. Low nitrogen generally affects plant growth and fruit quality. Melon, as an economic crop, is highly dependent on nitrogen. However, the response mechanism of its self-rooted and grafted seedlings to low-nitrogen stress has not been reported previously. Therefore, in this study, we analyzed the transcriptional differences between self-rooted and grafted seedlings under low-nitrogen stress using fluorescence characterization and RNA-Seq analysis. It was shown that low-nitrogen stress significantly inhibited the fluorescence characteristics of melon self-rooted seedlings. Analysis of differentially expressed genes showed that the synthesis of genes related to hormone signaling, such as auxin and brassinolide, was delayed under low-nitrogen stress. Oxidative stress response, involved in carbon and nitrogen metabolism, and secondary metabolite-related differentially expressed genes (DEGs) were significantly down-regulated. It can be seen that low-nitrogen stress causes changes in many hormonal signals in plants, and grafting can alleviate the damage caused by low-nitrogen stress on plants, ameliorate the adverse effects of nitrogen stress on plants, and help them better cope with environmental stresses. [ABSTRACT FROM AUTHOR]

It is generally recognized that the root uptake capacity of grafted plants strongly depends on the rootstocks' well-developed root system. However, we found that grafted plants showed different nitrate uptake capacities when different varieties of oriental melon scion were grafted onto the same squash rootstock, suggesting that the scion regulated the nitrate uptake capacity of the rootstock root. In this study, we estimated the nitrate uptake capacity of grafted plants with the different oriental melon varieties' seedlings grafted onto the same squash rootstocks. The results indicated a significant difference in the nitrate uptake rate and activity of two heterologous grafting plants. We also showed a significant difference in CmoNRT2.1 expression in the roots of two grafting combinations and verified the positive regulation of nitrate uptake by CmoNRT2.1 expression. In addition, the two varieties of oriental melon scion had highly significant differences in CmHY5 expression, which was transported to the rootstock and positively induced CmoHY5-1 and CmoHY5-2 expression in the rootstock roots. Meanwhile, CmHY5 could positively regulate CmoNRT2.1 expression in the rootstock roots. Furthermore, CmoHY5-1 and CmoHY5-2 also positively regulated CmoNRT2.1 expression, respectively, and CmoHY5-1 dominated the positive regulation of CmoNRT2.1, while CmHY5 could interact with CmoHY5-1 and CmoHY5-2, respectively, to jointly regulate CmoNRT2.1 expression. The oriental melon scion regulated the nitrate uptake capacity of the melon/squash grafting plant roots, and the higher expression of CmHY5 in the oriental melon scion leaves, the more substantial the nitrate uptake capacity of squash rootstock roots. [ABSTRACT FROM AUTHOR]

Root-zone CO2 is a major factor that affects crop growth, development, nutrient uptake, and metabolism. Oriental melon is affected by root-zone gases during growth, the microstructure, sugar and starch contents, enzymatic activities related to sugar and starch metabolism, and gene expression in the roots of oriental melon seedlings were investigated under three root-zone CO2 concentrations (CK: 0.2%, T1: 0.4%, T2: 1.1%). Elevated root-zone CO2 altered the cellular microstructure, accelerated the accumulation and release of starch grains, disrupted organelle formation, and accelerated root senescence. The sugar and starch contents and metabolic activity in the roots increased within a short duration following treatment. Compared to the control, 232 and 1492 differentially expressed genes (DEGs) were identified on the 6th day of treatment in T1 and T2 plants, respectively. The DEGs were enriched in three metabolic pathways. The majority of genes related to sucrose and starch hydrolysis were upregulated, while the genes related to sucrose metabolism were downregulated. The study revealed that oriental melon seedlings adapt to elevated root-zone CO2 stress by adjusting sugar and starch metabolism at the transcriptome level and provides new insights into the molecular mechanism underlying the response to elevated root-zone CO2 stress. [ABSTRACT FROM AUTHOR]

Root-zone CO2 is essential for plant growth and metabolism. However, the partitioning and assimilation processes of CO2 absorbed by roots remain unclear in various parts of the oriental melon. We investigated the time at which root-zone CO2 enters the oriental melon root system, and its distribution in different parts of the plant, using 13C stable isotopic tracer experiments, as well as the effects of high root-zone CO2 on leaf carbon assimilation-related enzyme activities and gene expressions under 0.2%, 0.5% and 1% root-zone CO2 concentrations. The results showed that oriental melon roots could absorb CO2 and transport it quickly to the stems and leaves. The distribution of 13C in roots, stems and leaves increased with an increase in the labeled root-zone CO2 concentration, and the δ13C values in roots, stems and leaves increased initially, and then decreased with an increase in feeding time, reaching a peak at 24 h after 13C isotope labeling. The total accumulation of 13C in plants under the 0.5% and 1% 13CO2 concentrations was lower than that in the 0.2% 13CO2 treatment. However, the distributional proportion of 13C in leaves under 0.5% and 1% 13CO2 was significantly higher than that under the 0.2% CO2 concentration. Photosynthetic carbon assimilation-related enzyme activities and gene expressions in the leaves of oriental melon seedlings were inhibited after 9 days of high root-zone CO2 treatment. According to these results, oriental melon plants' carbon distribution was affected by long-term high root-zone CO2, and reduced the carbon assimilation ability of the leaves. These findings provide a basis for the further quantification of the contribution of root-zone CO2 to plant communities in natural field conditions. [ABSTRACT FROM AUTHOR]

To study the influence of the Chinese high-speed railway ballastless track spectrum and the German low-interference spectrum on riding comfort, a long-span highway-railway suspension bridge is studied as an example, and a passenger–train–bridge coupling model is established based on the structural dynamics. The vibration responses of the passenger–train–bridge system during the CRH2C train running on the bridge are studied by a combination of the self-written computer program and general finite element software, considering the hunting movement, and the riding comfort of trains and passengers is evaluated using NMV and ISO-2631 standard, respectively. The results show that track irregularity has a few effects on the lateral vibration of the bridge. Compared with the German low-interference spectrum, the Chinese high-speed railway ballastless track spectrum has less exciting effects on the vibration of the passenger–train–bridge system and better riding comfort. Passengers in the middle of the train and on the middle seats of the same train have better riding comfort, and with the increase of train speed, the riding comfort of passengers will gradually reduce. Instead of passenger responses, the riding comfort classification based on the car body is overestimated. [ABSTRACT FROM AUTHOR]

Rhizosphere CO 2 is vital for crop growth, development, and productivity. However, the mechanisms of plants' responses to root-zone CO 2 are unclear. Oriental melons are sensitive to root-zone gas, often encountering high root-zone CO 2 during cultivation. We investigated root growth and nitrogen metabolism in oriental melons under T1 (0.5%) and T2 (1.0%) root-zone CO 2 concentrations using physiology and comparative transcriptome analysis. T1 and T2 increased root vigor and the nitrogen content in the short term. With increased treatment time and CO 2 concentration, root inhibition increased, characterized by decreased root absorption, incomplete root cell structure, accelerated starch accumulation and hydrolysis, and cell aging. We identified 1280 and 1042 differentially expressed genes from T1 and T2, respectively, compared with 0.037% CO 2 -grown plants. Among them, 683 co-expressed genes are involved in stress resistance and nitrogen metabolism (enhanced phenylpropanoid biosynthesis, hormone signal transduction, glutathione metabolism, and starch and sucrose metabolism). Nitrogen metabolism gene expression, enzyme activity, and nitrogen content analyses showed that short-term elevated root-zone CO 2 mainly regulated plant nitrogen metabolism post-transcriptionally, and directly inhibited it transcriptionally in the long term. These findings provided a basis for further investigation of nitrogen regulation by candidate genes in oriental melons under elevated root-zone CO 2 ., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.