Expression of anti-oxidant enzyme genes in scald-resistant 'Belfort' and scald-susceptible 'Granny Smith' apples during cold storage.

Real-Time PCR was used to determine whether the levels of mRNAs coding for anti-oxidant enzymes varied in apple peel during post-harvest cold storage, and if these were correlated with the occurrence of apple scald symptoms. Levels of the scald-related compounds, α-farnesene and conjugated trienes (CT; particularly, CT281 and CT258), were determined in fruit peel of the scald-resistant apple 'Belfort' and the scald-susceptible apple 'Granny Smith' during storage. α-Farnesene levels varied, irrespective of the incidence of scald, whereas the levels of CTs were correlated with the degree of scald. On the other hand, the level of H₂O₂ in 'Granny Smith' apple peel increased gradually, but significantly, from harvest during storage, whereas this value did not vary in 'Belfort' peel. In both apple cultivars, the levels of mRNA for Mn superoxide dismutase (MnSOD) decreased with storage time, whereas the levels of ascorbate peroxidase (APX) mRNA did not vary. In 'Granny Smith' apples, mRNA levels for catalase (CAT) increased dramatically (7.8-fold) late in the storage period. Monodehydro-ascorbate reductase (MDHAR) and glutathione reductase (GR) mRNA levels also increased greatly (12- and 18.8-fold, respectively) early in storage. Conversely, in 'Belfort' apples the transcript levels of these genes did not change during storage. These results indicate that scald- resistance in 'Belfort' apples was not directly related to higher levels of mRNAs for anti-oxidant enzymes. However, the higher levels of H₂O₂ in 'Granny Smith' apples was positively correlated with the higher levels of mRNAs for the anti-oxidant enzymes CAT, GR and MDHAR, suggesting direct regulation by the level of H₂O₂ on transcription of these anti-oxidant enzyme genes. [ABSTRACT FROM AUTHOR]