Figure 1.
Diagram of the biosynthetic pathway for polyphenol compounds, highlighting the cascade of compounds produced from phenylalanine and the action of the PPO enzyme.
Figure 2.
Trait distribution for L*, a* and b* parameters measured after 60 minutes of exposure to air.
The panels on the left are for POP_1 (‘Fuji x Pink Lady’), while the panels on the right are for POP_2 (‘Golden Delicious x Braeburn’). The grey bars in each panel represent the data distribution observed, while the black line is the normal fit of data. The x-axis gives the value for the three indexes, while the y-axis plots the number of observations.
The position of the four parental varieties is indicated by four letters: F_’Fuji’, PL_’Pink Lady’, GD_’Golden Delicious’ and B_’Braeburn’.
Figure 3.
Physical localization of the ten PPO genes discovered in the ‘Golden Delicious’ genome.
The position in Kb is plotted for each chromosome on the left , while the gene ID is shown on the right.
Figure 4.
QTL-LOD profile targeted on 6 linkage groups of the POP_1 and related to several flesh browning components.
In particular:.
LG9: b*_T0 (solid red).
LG10: L*T30-0 (solid green), a*_T30-0 (solid violet), L*_T60-0 (solid dark green), a*_T60-0 (dashed black), L*T30-0% (dashed blue), L*_T60-0% (dashed pink).
LG11: a*_T30 (solid dark green), b*_T30 (solid red), a*_T60 (solid blue), L*_T30-0 (solid green), a*_T30-0 (solid violet), b*_T30-0 (solid light blue), a*_T60-0 (dashed black), L*_T30-0% (dashed blue), a*_T30-0% (dashed yellow), L*_T60-0% (dashed pink), a*_T60-0% (dashed light green).
LG13: b*_T30 (solid blue).
LG14: b*_T30 (solid black), a*_T60 (solid yellow), b*_T60 (solid pink), L*_T60-30 (dashed red), a*_T60-30 (dashed green).
LG16: a*_T0 (solid black).
The QTL analysis was performed by using the phenotypic data of 47 seedlings of the POP_1. For each seedling a total of five apples were considered (biological replicates), and for each fruit the browning was measured on the two cut halves (technical replicates).
Figure 5.
Md-PPO haplotype validation in the POP_2 progeny.
White bars represent individuals characterised by a heterozygous haplotype (“np”), while the grey bars show the homozygous category (“nn”). The standard error is reported in each bar.
On the x-axis, 30-0 and 60-0 are the percentage variation of ∆ a* calculated between T30-T0 and T60-T0 respectively (2). indicates the ∆ value calculated after two months’ cold storage.
As for the analysis carried out for the POP_1, five apples (biological replicates) were assessed for each genotypes, and for each fruit the flesh browning was measured of the two halves (technical replicates).
Asterisks show statistically significant comparison based on the LSD-ANOVA test (P-value ≤ 0.05).
Figure 6.
Expression profile of the two genes involved in the polyphenolic pathway, PAL (Md-PAL, panel a) and PPO (Md-PPO, panel b).
In both graphs the y axis shows the mean normalised expression, graphing the three samples selected to monitor flesh browning (T0, T30 and T60).
Over the same time-course, the accumulation of the four main polyphenolic compounds, namely hydroxycinnamic acid (c), dihydrochalcones (d), flavan-3-ols (e) and flavonols (f), is shown below in the figure. The amount of these compounds is plotted on the y axis and expressed as μg/g of fresh weight (FW). Polyphenolic profiling was performed analyzing four replicates/experimental time.
For each bar the standard error is also reported.
Samples significantly different are shown using different letters following a LSD-ANOVA test (P-value ≤ 0.05).