Abstract
Flavonoids are secondary metabolites that play important roles in plant physiology. Despite numerous studies examined the effects of available carbon (C) or nitrogen (N) on flavonoid biosynthesis, the mechanism of C/N interactive effects on flavonoid metabolism is still unclear. In this study, we analyzed the composition of flavonoids and the expression levels of flavonoid-related genes in leaves and calli of crabapple (Malus sp.) cultivars with different leaf colors grown on media with different C/N ratios. Our results show that high C/N ratios induce anthocyanin pigmentation in leaves of the ever-red cultivar ‘Royalty’ and the spring-red cultivar ‘Prairifire,’ as well as in three types of calli derived from the ever-green cultivar ‘Spring Snow,’ but not in the leaves of the ever-green cultivar ‘Flame.’ This phenomenon therefore correlated with anthocyanin content in these different samples. In addition, high C/N ratios in the growth media resulted in an increase in the concentration of flavones and flavonols in the leaves of the three crabapple cultivars. The transcript levels of the general flavonoid pathway genes [from chalcone synthase (CHS) to uridine diphosphat-glucose: flavonoid 3-O-glycosyltransferase (UFGT) and flavonol synthase (FLS)] increased in response to high C/N ratios, and this in turn was correlated with the concentration of anthocyanins, flavones and flavonols in the leaves and calli. Expression of the late flavonoid/anthocyanin biosynthetic genes, anthocyanidin synthase (ANS), UFGT and FLS in particular, was more strongly influenced by C/N ratios than other structural genes, and the increased expression of the structural genes under high C/N ratios coincided with a coordinated increase in transcript levels of a MYB transcription factor, MYB10. These results are likely to be useful for future generation of plants with an optimized flavonoid/anthocyanin content or desirable organ coloration.
Highlights
Atmospheric carbon dioxide (CO2) concentration is projected to rise to 500–1000 mmol mol−1 by the end of this century (Susan, 2007), and this increase will accelerate the greenhouse effect and alter the C and N balance in the global ecosystem (Carlisle et al, 2012; Fulweiler et al, 2014)
220 bp 182 bp 233 bp 108 bp 126 bp 202 bp 194 bp 120 bp 102 bp Carbon and Nitrogen Balance can Affect the Growth of Crabapple To investigate the influence of the C and N nutrient balance on the growth of crabapple, plantlets of ‘Royalty,’ ‘Prairifire,’ and ‘Flame,’ as well as three types of calli, were grown on modified Murashige and Skoog medium (MS) media containing various C/N levels
With respect to the plantlets, in media with 60N, increasing C from 30 to 270 mM led to an increase in fresh weight (FW) for ‘Royalty,’ ‘Prairifire,’ and ‘Flame,’ with the highest FW increment at 270, 150, and 270 mM, respectively (Figure 1A)
Summary
Atmospheric carbon dioxide (CO2) concentration is projected to rise to 500–1000 mmol mol−1 by the end of this century (Susan, 2007), and this increase will accelerate the greenhouse effect and alter the C and N balance in the global ecosystem (Carlisle et al, 2012; Fulweiler et al, 2014). The availability of CO2 is regarded as one of the major limiting factors in photosynthesis, which is the mechanism by which carbohydrates are synthesized for subsequently use as an energy source and to provide C-skeletons for plant metabolism, growth, and development (Broadmeadow and Jackson, 2000; Jaafar et al, 2012; Sun et al, 2012). Cellular C and N metabolism must be tightly coordinated to sustain optimal growth and development in plants and other organisms Carbohydrates can provide both the energy and the C-skeletons used for N assimilation during amino acid biosynthesis, while amino acids and proteins are the key building blocks for the cell (Coruzzi and Zhou, 2001). Despite numerous studies focusing on the biochemical and physiological aspects of C or N metabolism (Tallis et al, 2010; Sun et al, 2012; Fulweiler et al, 2014; Takatani et al, 2014; Marble et al, 2015), there is still a lack of a detailed understanding of the molecular mechanisms underlying the interaction between C and N
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