BackgroundChimeras synthesized artificially by grafting are crucial to the breeding of perennial woody plants. ‘Hongrou Huyou’ (Citrus changshan-huyou + Citrus unshiu) is a new graft chimera originating from the junction where a Citrus changshan-huyou (“C”) scion was top-grafted onto a stock Satsuma mandarin ‘Owari’ (C. unshiu, “O”). The chimera was named OCC because the cell layer constitutions were O for Layer 1(L1) and C for L2 and L3. In this study, profiles of primary metabolites, volatiles and carotenoids derived from different tissues in OCC and the two donors were investigated, with the aim of determining the relationship between the layer donors and metabolites.ResultsThe comparison of the metabolite profiles showed that the amount and composition of metabolites were different between the peels and the juice sacs, as well as between OCC and each of the two donors. The absence or presence of specific metabolites (such as the carotenoids violaxanthin and β-cryptoxanthin, the volatile hydrocarbon germacrene D, and the primary metabolites citric acid and sorbose) in each tissue was identified in the three phenotypes. According to principal component analysis (PCA), overall, the metabolites in the peel of the chimera were derived from donor C, whereas those in the juice sac of the chimera came from donor O.ConclusionThe profiles of primary metabolites, volatiles and carotenoids derived from the peels and juice sacs of OCC and the two donors were systematically compared. The content and composition of metabolites were different between the tissues and between OCC and the each of the two donors. A clear donor dominant pattern of metabolite inheritance was observed in the different tissues of OCC and was basically consistent with the layer origin; the peel of the chimera was derived from C, and the juice sacs of the chimera came from O. These profiles provide potential chemical markers for genotype differentiation, citrus breeding assessment, and donor selection during artificial chimera synthesis.

The diversity of fruit color in sweet cherry (Prunus avium L.) has been attributed to the presence of either anthocyanin or carotenoid. We profiled the anthocyanin and carotenoid metabolites to investigate the different pigments and the underlying regulatory mechanisms of differential expression genes (DEGs) between red and yellow fruits of sweet cherry. We profiled two cultivars, ‘Jiangnanhong’(JNH, red fruits) and ‘Chaoyang’(CY, yellow fruits) to establish their anthocyanin and carotenoid metabolites by LC-MS/MS and transcriptome analysis by RNA-seq to test the difference in gene expression and metabolic substances between the two varieties. Cyanidin-3-O-rutinoside was the most different pigment between two cultivars, the content of which in red fruit was significantly higher than in the yellow one during the whole ripening stage (stage 3 and stage 4). The total carotenoid content in the two color types of fruits was close, but the content in yellow fruit was shown to be more stable after harvest. Based on the transcriptome data, the heatmap of selected structural DEGs showed that all of the anthocyanin genes expressed significantly higher levels in red fruits than that in yellow fruits. Two unigenes encoding chalcone synthase (CHS) and UDP glucose-flavonoid 3-O-glucosyltransferase (UFGT) were expressed 1134.58 and 1151.24 times higher in red than in yellow fruits at stage 4, respectively. Correlation analysis showed that anthocyanin genes in JNH were negatively correlated with those in CY; by contrast, there were some strong correlations observed between the two cultivars in carotenoid genes. Thus, the coloration of sweet cherry was mainly attributed to anthocyanin-related genes.

The effect of carnauba wax-based nanoemulsion coating-1 (NC-1) combined with 1-methylcyclopropene (1-MCP) treatment on the storage of honey peach fruit 'Yulupantao' for 28 days under 0 AE 0.5 °C, and 90% RH conditions was studied. The results showed that NC-1 or 1-MCP treatment alone and in combination were proved to be more effective in maintaining fruit qualities compared to the control group with no treatment. However, the application with the combination of NC-1 and 1-MCP treatment had the most significant effect on reducing mass loss and decay rate, maintaining firmness, total soluble solids (TSS), ascorbic acid (AsA) and titratable acid (TA) contents, suppressing malondialdehyde (MDA) accumulation and conductivity ascend. Moreover, the activities of peroxidase (POD) were maintained, and polyphenol oxidase (PPO) and phenylalanine ammonialyase (PAL) were effectively suppressed in NC-1, 1-MCP and combined treatment than that of control. Therefore, the combination of NC-1 and 1-MCP treatment could be an efficient way to maintain the qualities of peach fruit during low-temperature storage after harvest.

Background: Graft chimeras can be synthesized out, which is crucial to cultivar breeding. A new graft chimera named ‘Hongrou Huyou’, simply as OCC (the cell layers constitutions were ‘O’ for L1 and ‘C’ for L2 & L3, determined by ‘Owari’ satsuma mandarin and ‘Changshan Huyou’, respectively) was found at the junction where a scion C top-grafted onto a stock O, in an orchard in Changshan county, Quzhou city of Zhejiang province. This study investigated the primary metabolites, volatiles and carotenoids of OCC, aiming to figure out which substances are derived from layer source donors and which are newly generated by genetic regulation and interaction of two donors. Results: Based on statistical similarity analysis, the main results indicated that some substances in peels of OCC, such as 4-aminobutanoic acid, and palmitic acid were derived from C, while others in juice sacs, such as 4-aminobutanoic acid and palmitic acid were produced by O. Among those identical compounds observed in three cultivars, the concentrations of 13 and 7 compounds in OCC were significantly higher and lower than those in any of the donors, respectively. Especially, Germacrene D even exceeded 6-17 times than two donors in juice sacs. Interestingly, α-ylangene was herein exclusively observed in OCC and were rarely reported in any other citrus species, this was probably due to the interactions of cell layers from different genotypic donor parents and then lead to addictive effect in chimeras; the presence and absence of some profiles, such as the disappearance of α-carotene in C, can be used for genotype differentiation and citrus breeding assessment. Conclusion: Our results first systematically provide a chemical characterization of a citrus chimera, and found the genetic regularity of chemical substances and put forward some predictions on donor-controlled and autonomous metabolic patterns in plant chimeras. This work provide a theory guidance for synthetic chimera and diversity of certain chemical-preserved cultivars can try to be obtained in this way. Key words: Citrus, Periclinal chimera, Metabolites, Volatiles, Carotenoids