Chilling stress increases the amount of polyphenols, especially lignin, which protects tobacco (Nicotiana tabacum L. cv. k326) from chilling stress. To clarify the molecular biosynthesis mechanism of the key representative compounds, specifically lignin, RNA sequencing and ultra-high pressure liquid chromatography coupled to quadrupole-time of flight mass spectrometry technologies were used to construct transcriptomic and metabolomic libraries from the leaves of tobacco plants subjected to normal (25°C) and chilling (4°C) temperature treatments. Transcriptomic libraries from the different samples were sequenced, generating more than 40 million raw reads. Among nine samples, metabolomic analysis identified a total of 97 encoding enzymes that function in the key steps of pathways related to polyphenol biosynthesis, where 42 metabolites were also located. An integrated analysis of metabolic and transcriptomic data revealed that most of the intermediate metabolites and enzymes related to lignin biosynthesis were synthesised in the leaves under chilling stress, which suggests that the biosynthesis of lignin plays an important role in the response of tobacco leaves to cold temperatures. In addition, the cold insensitivity of chalcone synthase genes might be considered to be an important rate-limiting factor in the process of precursor substance flow to flavonoid biosynthesis under chilling stress. Furthermore, the upregulated expression of phenylalanine ammonia lyase (PAL), hydroxycinnamoyl transferase (HCT) and cinnamyl-alcohol dehydrogenase (CAD) under chilling stress is the key to an increase in lignin synthesis. This study provides a hypothetical basis for the screening of new active metabolites and the metabolic engineering of polyphenols in tobacco.

Drought stress is one of the main factors limiting crop production, which provokes a number of changes in plants at physiological, anatomical, biochemical and molecular level. To unravel the various mechanisms underpinning tobacco (Nicotiana tabacum L.) drought stress tolerance, we conducted a comprehensive physiological, anatomical, biochemical and transcriptome analyses of three tobacco cultivars (i.e., HongHuaDaJinYuan (H), NC55 (N) and Yun Yan-100 (Y)) seedlings that had been exposed to drought stress. As a result, H maintained higher growth in term of less reduction in plant fresh weight, dry weight and chlorophyll content as compared with N and Y. Anatomical studies unveiled that drought stress had little effect on H by maintaining proper leaf anatomy while there were significant changes in the leaf anatomy of N and Y. Similarly, H among the three varieties was the least affected variety under drought stress, with more proline content accumulation and a powerful antioxidant defense system, which mitigates the negative impacts of reactive oxygen species. The transcriptomic analysis showed that the differential genes expression between HongHuaDaJinYuan, NC55 and Yun Yan-100 were enriched in the functions of plant hormone signal transduction, starch and sucrose metabolism, and arginine and proline metabolism. Compared to N and Y, the differentially expressed genes of H displayed enhanced expression in the corresponding pathways under drought stress. Together, our findings offer insights that H was more tolerant than the other two varieties, as evidenced at physiological, biochemical, anatomical and molecular level. These findings can help us to enhance our understanding of the molecular mechanisms through the networks of various metabolic pathways mediating drought stress adaptation in tobacco.

Reasonable canopy structure and leaf physiological characteristics are considered as important factors for improving canopy nitrogen (N) distribution by matching the available light resources and thus increasing the grain yield of maize (Zea mays L.). However, the determinants of different maize varieties in light–N matching and grain yields with specific canopy structures and leaf physiological characteristics, as well as the response to the N application rate, remain poorly understood. In this study, we analyzed the relationships between different canopy structures and the enzyme activity and light utilization of spring maize in the field. Two maize varieties (XY335 and ZD958) with different canopy structures were used as the experimental material in a 2-year field experiment from 2014 to 2015, grown under different N inputs of 0, 100, 200, and 300 kg N ha⁻¹ (N0, N1, N2, and N3) at a planting density of 90,000 plants ha⁻¹ in Jilin Province on the Northeast China Plain. The results show that XY335 combined with N3 had a greater leaf angle, upper internode length and number, and upper leaf area index of the upper layer compared with ZD958. Higher N assimilatory enzyme (glutamine synthase (GS), glutamate synthase (GOGAT), and nitrate reductase (NR)) activities in the upper and middle leaves were observed in XY335 compared to ZD958. Furthermore, the light interception and light utilization efficiency of the upper leaves of XY335 increased, especially at higher N application rates, which significantly affected the N translocation post-silking and its distribution in different populations. As a result, the photosynthetic N use efficiency (PNUE) values of the upper leaves (10.4%) and middle leaves (5.2%) of XY335 were higher than those of ZD958, coordinating the canopy light and N distributions and being positively correlated with the maize grain yield. This suggested that the superior canopy structure of the upper layer and N assimilatory enzymes of the upper and middle leaves of this maize variety significantly increased the light interception of the canopy, while the synchronization of light and the N of the upper and middle leaves increased the light and N utilization efficiency of maize, which ultimately increased the grain yield at a high plant density.