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Carrot is a root crop consumed worldwide and has great nutritional qualities. It is considered as one of the ten most important vegetable crops. Cytokinins are an essential class of the plant hormones that regulate many processes of plant growth. Till now, the effects of cytokinin, BAP, on lignin biosynthesis and related gene expression profiles in carrot taproot is unclear. In order to investigate the effect of applied BAP on lignin-related gene expression profiles, lignin accumulation, anatomical structures, and morphological characters in carrot taproots. Carrot roots were treated with different concentrations of BAP (0, 10, 20, and 30 mg L -1 ). The results showed that the application of BAP significantly increased plant length, shoot fresh weight, root fresh weight, and taproot diameter. In addition, BAP at 20 mg L -1 or 30 mg L -1 enhanced the average number of petioles. BAP treatment led to increased number and width of xylem vessels. The parenchyma cell numbers of pith were significantly induced in taproots treated with the BAP at a concentration of 30 mg L -1 . BAP significantly upregulated most of the expression levels of lignin biosynthesis genes, caused elevated lignin accumulation in carrot taproots. Our results indicate that BAP may play important roles in growth development and lignification in carrot taproots. Our results provide a valuable database for more studies, which may focus on the regulation of root lignification via controlling cytokinin levels in carrot taproots.

The NAC transcription factor participates in various biotic and abiotic stress responses and plays a critical role in plant development. Lignin is a water-insoluble dietary fiber, but it is second only to cellulose in abundance. Celery is the main source of dietary fiber, but its quality and production are limited by various abiotic stresses. Here, AgNAC1 containing the NAM domain was identified from celery. AgNAC1 was found to be a nuclear protein. Transgenic Arabidopsis thaliana plants hosting AgNAC1 have longer root lengths and stomatal axis lengths than the wide type (WT). The evidence from lignin determination and expression levels of lignin-related genes indicated that AgNAC1 plays a vital role in lignin biosynthesis. Furthermore, the results of the physiological characterization and the drought and salt treatments indicate that AgNAC1-overexpressing plants are significantly resistive to salt stress. Under drought and salt treatments, the AgNAC1 transgenic Arabidopsis thaliana plants presented increased superoxide dismutase (SOD) and peroxidase (POD) activities and decreased malondialdehyde (MDA) content and size of stomatal apertures relatively to the WT plants. The AgNAC1 served as a positive regulator in inducing the expression of stress-responsive genes. Overall, the overexpressing AgNAC1 enhanced the plants' resistance to salt stress and played a regulatory role in lignin accumulation., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Gibberellin (GA) is a phytohormone of a biguanide compound that plays an important role throughout the life cycle of a plant. Lignin, a phenylalanine-derived aromatic polymer, can enhance the water transport function and structural resistance of cell walls. This function is also the core on biology of higher terrestrial plants. An appropriate lignin level is important to the quality of leafy vegetables, such as celery. The relationship between gibberellin levels and the occurrence of lignification has not been reported in celery. In this study, the leaf blades and petioles of celery cultivars 'Liuhe Huangxinqin' and 'Jinnan Shiqin' were used as materials, and different concentrations of exogenous gibberellin were applied to analyze the growth and lignin distribution of leaf blades and petioles. It was found that gibberellin treatment could influence the lignin content in celery leaves. Autofluorescence analysis under ultraviolet (UV) excitation showed that gibberellin treatment caused lignification of celery leaf tissue. The expression profiles of 12 genes related to lignin synthesis changed with the increase of gibberellin concentration. Our results showed that gibberellin played a significant role in the accumulation of lignin in the development of celery leaves. This provides a basis for further study on the regulation of lignin metabolism in plants and exerts a vital part in the application of plant growth regulators to production.

In our study, isobaric tags for relative and absolute quantification (iTRAQ) was conducted to determine the significantly changed proteins in the fleshy roots of carrots under different carbon dioxide (CO 2 ) treatments. A total of 1523 proteins were identified, of which 257 were differentially expressed proteins (DEPs). On the basis of annotation analysis, the DEPs were identified to be involved in energy metabolism, carbohydrate metabolism, and some other metabolic processes. DcC4H and DcPER, two lignin-related proteins, were identified from the DEPs. Under elevated CO 2 stress, both carrot lignin content and the expression profiles of lignin biosynthesis genes changed significantly. The protein-protein interactions among lignin-related enzymes proved the importance of DcC4H and DcPER. The results of our study provided potential new insights into the molecular mechanism of lignin content changes in carrot roots under elevated CO 2 stress.

Key Message: Hypoxia enhances lignification of carrot root. Hypoxia stress was thought to be one of the major abiotic stresses that inhibiting the growth and development of higher plants. The genes encoding the plant alcohol dehydrogenase (ADH-P) were induced when suffering hypoxia. To investigate the impact of hypoxia on the carrot root growth, carrot plants were cultivated in the hydroponics with or without aeration. Morphological characteristics, anatomical structure, lignin content, and the expression profiles of DcADH-P genes and lignin biosynthesis-related genes were measured. Six DcADH-P genes were identified from the carrot genome. The expression profiles of only three (DcADH-P1, DcADH-P2, and DcADH-P3) genes could be detected and the other three (DcADH-P4, DcADH-P5, and DcADH-P6) could not be detected when carrot cultivated in the solution without aeration. In addition, carrot roots had more lignin content, aerenchyma and less fresh weight when cultivated in the solution without aeration. These results suggested that hypoxia could enhance the lignification and affect anatomical structure of the carrot root. However, the expression levels of the genes related to lignin biosynthesis were down-regulated under the hypoxia. The enhancement of lignification may be the consequence of the structure changes in the carrot root. Our work was potentially helpful for studying the effect of hypoxia on carrot growth and may provide useful information for carrot hydroponics.

Carbon dioxide (CO 2 ) is an important regulator of plant growth and development, and its proportion in the atmosphere continues to rise now. Lignin is one of the major secondary products in plants with vital biological functions. However, the relationship between CO 2 level and xylogenesis in celery is still unknown. In order to investigate the effects of increasing CO 2 concentration on lignin accumulation in celery, 'Jinnanshiqin' were exposed to two CO 2 applications, 400 (e 0 ) and 1000 μmol mol -1 (e 1 ), respectively. Plant morphology and lignin distribution in celery plants treated with elevated CO 2 did not change significantly. There was an upward trend on lignin content in celery leaves, and the transcript abundance of 12 genes involved in lignin metabolism has altered in response to elevated CO 2 . The effects of high level of CO 2 on different tissues were different. Our works confirmed that CO 2 may play an important role in lignin accumulation in celery leaves. The current study will offer new evidence to understand the regulation mechanism of lignin biosynthesis under elevated CO 2 and provide a reference to improve celery quality by adjusting the growth environment., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

Gibberellins (GAs) are important growth regulators involved in plant development processes. However, limited information is known about the relationship between GA and xylogenesis in carrots. In this study, carrot roots were treated with GA 3 . The effects of applied GA 3 on root growth, xylem development, and lignin accumulation were then investigated. Results indicated that GA treatment dose-dependently inhibited carrot root growth. The cell wall significantly thickened in the xylem parenchyma. Autofluorescence analysis with ultraviolet (UV) excitation indicated that these cells became lignified because of long-term GA 3 treatment. Moreover, lignin content increased in the roots, and the transcripts of lignin biosynthesis genes were altered in response to applied GA 3 . Our data indicate that GA may play important roles in xylem growth and lignification in carrot roots. Further studies shall focus on regulating plant lignification, which may be achieved by modifying GA levels within plant tissues.

Key Message: Carrot root development associates lignin deposition and regulation. Carrot is consumed worldwide and is a good source of nutrients. However, excess lignin deposition may reduce the taste and quality of carrot root. Molecular mechanisms underlying lignin accumulation in carrot are still lacking. To address this problem, we collected taproots of wild and cultivated carrots at five developmental stages and analyzed the lignin content and characterized the lignin distribution using histochemical staining and autofluorescence microscopy. Genes involved in lignin biosynthesis were identified, and their expression profiles were determined. Results showed that lignin was mostly deposited in xylem vessels of carrot root. In addition, lignin content continuously decreased during root development, which was achieved possibly by reducing the expression of the genes involved in lignin biosynthesis. Carrot root may also prevent cell lignification to meet the demands of taproot growth. Our results will serve as reference for lignin biosynthesis in carrot and may also assist biologists to improve carrot quality.

Celery of the family Apiaceae is a biennial herb that is cultivated and consumed worldwide. Lignin is essential for cell wall structural integrity, stem strength, water transport, mechanical support, and plant pathogen defense. This study discussed the mechanism of lignin formation at different stages of celery development. The transcriptome profile, lignin distribution, anatomical characteristics, and expression profile of leaves at three stages were analyzed. Regulating lignin synthesis in celery growth development has a significant economic value. Celery leaves at three stages were collected, and Illumina paired-end sequencing technology was used to analyze large-scale transcriptome sequences. From Stage 1 to 3, the collenchyma and vascular bundles in the petioles and leaf blades thickened and expanded, whereas the phloem and the xylem extensively developed. Spongy and palisade mesophyll tissues further developed and were tightly arranged. Lignin accumulation increased in the petioles and the mesophyll (palisade and spongy), and the xylem showed strong lignification. Lignin accumulation in different tissues and at different stages of celery development coincides with the anatomic characteristics and transcript levels of genes involved in lignin biosynthesis. Identifying the genes that encode lignin biosynthesis-related enzymes accompanied by lignin distribution may help elucidate the regulatory mechanisms of lignin biosynthesis in celery.

White celery (Apium graveolens L.), a variety of common celery, is an important leafy vegetable in the Apiaceae family and is famous for its nutritional value. However, limited work has been devoted to quality formation and regulation in white celery. In this study, four white celery varieties, 'Xuebaiqincai', 'Saixue', 'Baiganshiqin' and 'Ruixue', were selected and analyzed for the comparison of ascorbic acid (AsA) and lignin levels, which are two important quality evaluation indicators in celery. The expression levels of the genes involved in AsA and lignin metabolic pathways were also detected. In the leaf blades, the AsA content was highest in 'Xuebaiqincai' compared with other varieties, whereas the most abundant AsA levels in the petioles were observed in 'Baiganshiqin' and 'Ruixue'. The expression levels of AsA-related genes varied among the studied varieties. The highest level was detected in 'Xuebaiqincai', whereas other varieties exhibited relatively lower levels. The lignin content in the leaf blades was lower than that in the petioles. Correspondingly, the transcript profiles of genes involved in lignin biosynthesis were in accordance with the different levels in the petioles and blades. The results of this study provide potentially useful information for white celery breeding aimed at quality improvement and regulation. [ABSTRACT FROM AUTHOR]

Increasing the level of AsA and maintaining proper lignin content will improve the quality of celery (Apium graveolens L.). However, the study on the regulation mechanism of genes related to AsA and lignin metabolism in celery was limited, especially in yellow celery. In this study, the accumulation of AsA and lignin and the expression profiles of related-genes were detected in three kinds of yellow celery. The results showed that the content of AsA was higher in the leaf blades of 'Huangtaiji' and the petioles of 'Jinhuangqincai'. The content of lignin was the highest in 'Jinhuangqincai' leaves, followed by 'Liuhehuangxinqin' and 'Huangtaiji'. The expression levels of AgAO (r = −0.032) and AgDHAR1 (r = −0.193) genes involved in AsA recycling and degradation showed negatively correlated with AsA content. AgCCoAOMT (r = 0.692) and AgF5 H (r = 0.733) genes expression were positively correlated with lignin content, while the expression of AgCAD (r = −0.694) and AgC3ʹH (r = −0.722) genes were negatively correlated with lignin content. Our current work provided potential theoretical basis for effectively changing accumulation of AsA and lignin by genetic engineering in celery. [ABSTRACT FROM AUTHOR]