Figure 3. Relative mRNA expression for genes encoding enzymes involved in sugar metabolism (including MdSDHs, MdCWINVs, MdNINVs, MdvAINVs, MdSUSYs, MdFKs, MdHKs, MdSPSs) during apple fruit development.

Quantitative RT-PCR was performed with gene-specific primers, except for MdSDH2-9 where a pair of universal primer was designed from the conserved cDNA region of MdSDH2 to MdSDH9. For each sample, transcript levels were normalized with those of Actin, and the relative expression levels of each gene were obtained using the ddCT method while expression in 40-DAB-fruit was designated as ‘10’. Values are means of three replicates of the reverse transcribed RNA sample pooled from 5 biological replicates ± SD.