Figures (5)  Tables (2)

    • Figure 1. 

      The biosynthetic pathway of ascorbic acid in higher plants (D-mannose/L-galactose pathway). The reactions catalyzed by the enzymes are numbered as follows: 1. HXK (hexokinase); 2. PGI (phosphoglucose isomerase); 3. PMI (phosphomannose isomerase); 4. PMM (phosphomannomutase); 5. GMP (GDP-D-mannose pyrophosphorylase); 6. GME (GDP-D-mannose 30,50-epimerase); 7. GGP (GDP-L-galactose phosphorylase); 8. GPP (L-galactose-1-P phosphatase); 9. L-GalDH (L-galactose dehydrogenase); 10. GLDH (L-galactono-1,4-lactone dehydrogenase). VTC2 and VTC5 catalyze the first commitment step in the synthesis of GGP from L-ascorbic acid (step 7).

    • Figure 2. 

      Effect of leaf shading (a, b), fruit shading (c, d), and both types of shading (e, f) on total ascorbic acid (a, c, e) and reduced ascorbic acid content (b, d, f) in fruits which were harvested at immature green (IMG), mature (MG), breaker (BR) and red ripe (RR) stages of fruits in plants. LS, leaf shading; FS, fruit shading; BS, both shading. Data is presented as mean ± SD. Statistical analysis was enforced using Duncan's test. The indication of * and ** is a significant difference at P ≤ 0.05 and P ≤ 0.01, respectively.

    • Figure 3. 

      The mRNA transcription level of AsA biosynthetic genes in S. lycopersicum 'Ailsa Craig' at immature green (IMG), mature green (MG), breaker (BR) and red ripe (RR) stages with or without leaf shading. US, un-shaded; LS, leaf shading. Data is presented as mean values ± SD (n = 3). * and ** illustrate a significant difference at P < 0.05 and P < 0.01 levels, respectively.

    • Figure 4. 

      The relative mRNA transcription of AsA biosynthetic genes in S. lycopersicum 'Ailsa Craig' at immature green (IMG), mature green (MG), breaker (BR) and red ripe (RR) fruits with or without fruit shading. US, un-shaded; FS, fruit shading. Data is presented as mean values ± SD (n = 3). * and ** indicate significant difference at P ≤ 0.05 and P ≤ 0.01 levels, respectively.

    • Figure 5. 

      The effect of leaf and fruit shading on the expression level of AsA biosynthetic genes in S. lycopersicum 'Ailsa Craig' at immature (IMG), mature (MG), breaker (BR) and red ripe (RR) fruits. US, un-shaded; BS, Both shading of leaf and fruits. Data is presented as mean values ± SD (n = 3). The * and ** illustration is a significant difference at P ≤ 0.05 and P ≤ 0.01, respectively.

    • FunctionGeneFull nameAccession No.Forward primer (5'-3')Reverse primer (5'-3')
      synthesisGPIglucose-6-phosphate isomeraseSolyc04g076090TGCTCTTCAAAAGCGTGTCCCGGCAATAAGTGCTCTGTCA
      PMIphosphomannose isomeraseSolyc02g086090TACATTGTGGTGGAACGAGGAACCCCATTTGGCAAGAACAG
      PMMphosphomannomutaseSolyc05g048760TTTACCCTCCATTACATTGCTGATCTTCTTGACTACAGTTTCTCCCA
      GMPGDP-D-mannose pyrophosphorylaseSolyc03g096730AAACCTGAAATCGTGATGTGAGATGAAGAAGAGGAGAACTGGAAAC
      GME1GDP-Mannose 3′,5′-epimerase1Solyc01g097340AATCCGACTTCCGTGAGCCCTGAGTTGCGACCACGGAC
      GME2GDP-Mannose 3′,5′-epimerase2Solyc04g077020CCATCACATTCCAGGACCAGACGTAATCCTCAACCCATCCTT
      GGP1GDP-L-galactose-1-phosphate phosphorylase1Solyc06g073320GAAATCTGGTCTGTTCCTCTGTGATTCACACACCAACTCCACATTACA
      GGP2GDP-L-galactose-1-phosphate phosphorylase2Solyc02g091510CTGTTGTCTTGGTTGGAGGTTGTAGCACAGTCAAAACACCAACAAA
      GP1L-galactose-1-phosphate phosphatase1Solyc04g014800AGCCGCTACAAACCCTCATCTTGTCCGCTTTCCATCTCCTAT
      GP2L-galactose-1-phosphate phosphatase2Solyc11g012410GGTTAGGTCCCTTCGTATGTGTTTCACAATCACAGCACCACC
      GalDHL-galactose dehydrogenaseSolyc01g106450CTTCTTACTGAGGCTGGTGGTCAACCTCTTTAACAGACTTCATCCC
      MIOXmyo-inositol oxygenaseSolyc12g008650ACTACTCTTCCTTCTGCTGCTTTAAATGTTGAGCCACTTCATGTTCT
      recyclingDHAR1dehydroascorbate reductase 1Solyc05g054760CCTACCTTCGTCTCATTTCCGTGAACAAACATTCTGCCCATT
      oxidationcAPXCytoplasm ascorbate peroxidaseSolyc06g005150TGGAGCCCATTAGGGAGCAGCCAGGGTGAAAGGGAACAT
      tAPXThylakoidal ascorbate peroxidaseSolyc11g018550CTTTCTTCAATGGCTTCTCTCACCGCAACCTGGTAGCGAAACACATGGG
      APX1ascorbate peroxidase 1Solyc06g005160TGGAGCCCATTAGGGAGCAGCCAGGGTGAAAGGGAACAT
      APX4ascorbate peroxidase 4Solyc01g111510GGAACAGTTCCCAATCCTATCCCATAGGTTCCTGCATCATGCCACC
      APX5ascorbate peroxidase 5Solyc02g083620AGTAGATGCAGAGTATCTGAAGGACATAGGTTCCTGCATCATGCCACC
      APX7Stromal ascorbate peroxidase 7Solyc06g060260CTTTCTTCAATGGCTTCTCTCACCGCAACCTGGTAGCGAAACACATGGG
      ActinActinSolyc11g005330GTCCTCTTCCAGCCATCCAACCACTGAGCACAATGTTACCG

      Table 1. 

      Primers used for qPCR.

    • GenesGPIPMIPMMGMPGME1GME2GGP1GGP2GP1GP2GalDHMIOXDHAR1cAPXtAPXAPX1APX4APX5APX7
      rT-AsA US0.5*−0.69*−0.63*−0.01−0.36−0.85*−0.82*−0.14−0.57*−0.08−0.69*−0.75*0.080.20.26−0.07−0.75*−0.61*−0.37
      rT-AsA LS−0.63*0.83*0.66*−0.030.58*0.88*0.76*0.55*0.67*0.140.77*0.450.27−0.25−0.250.29 0.81*0.75**0.53*
      rT-AsA FS−0.340.61*0.54*0.010.79*0.73*0.96**0.6*0.51*0.250.71*0.59*0.220.31−0.310.080.9**0.51*0.16
      rT-AsA BS0.10.90**0.47−0.090.91**0.97**0.94**0.69*0.490.54*0.20.67*0.110.26−0.1−0.080.95**0.75*0.13
      rAsA US0.55*-0.62*-0.52*0.14−0.38−0.77*−0.78*−0.09−0.46−0.18−0.59*−0.66*0.160.110.290.32−0.68*−0.52*−0.26
      rAsA LS−0.40.83*0.39−0.130.81*0.93**0.91**0.6*0.57*0.5*0.65*0.180.110.13−0.240.40.67*0.63*0.3
      rAsA FS−0.250.67*0.52*0.130.74*0.8*0.91**0.64*0.56*0.140.78*0.69*0.280.21−0.280.170.91**0.6*0.29
      rAsA BS0.170.86*0.43−0.110.88*0.94**0.92**0.68*0.440.56*0.160.62*0.110.34−0.09−0.090.91**0.72*0.09
      * and ** indicate a significant correlation at P < 0.05 and P < 0.01, respectively.

      Table 2. 

      The correlation coefficient between AsA biosynthetic gene expression and AsA accumulation in fruits with shading or un-shaded treatment.