Wednesday, August 18
The expression pattern of primary metabolism key-genes is differentially affected in apple cortex following the oxygen concentration shift applied in DCA storage protocols
Wednesday, August 18
3:20 pm - 3:35 pm


The dynamic controlled atmosphere (DCA) technique is based on the use of oxygen levels that are kept at extremely low values (about 0.3−0.4 kPa), close to the anaerobic compensation point. These conditions may cause negative consenquences on fruits in particular if this hypoxic stress is excessively prolonged. On the basis of specific parameters that are effective in assessing the stress level reached by the fruit (e.g. ethanol production), the oxygen level is increased up to a “safe” concentration (about 0.8−0.9 kPa). The responses of apples to this oxygen shift result in primary metabolite profile and gene expression changes. We analyzed the expression pattern of selected genes in the cortex of two different apple varieties (Granny Smith, GS, and Stark Red Delicious, RD) after 24h and 7 days from the shift of oxygen concentration from 0.4 to 0.8 kPa. In GS, alcohol dehydrogenase (ADH), phosphofructokinase (PFK) and pyruvate kinase (PK) genes resulted to be rapidly (24h after the oxygen level shift) down-regulated, suggesting that the glycolytic and fermentative pathways undergo a rapid re-adjustment. A rapid response in terms of amino acid metabolism was also hypothesized based on the observed down-regulation of genes encoding enzymes of the serine-, alanine-, and glycine-biosynthesis pathways. Molecular responses to oxygen re-supply appear to change depending on the timing of the oxygen shift application with respect to the storage duration at 0.4 kPa. Among the primary metabolism studied genes (ADH; PFK; alanine amino transferase, AlaAT; β-amylase, AMY; sucrose synthase, SuSy; pyruvate decarboxylase, PDC), PFK and SuSy expression showed a different pattern of relative expression 7 days after the oxygen shift applied following 1 or 11 weeks of storage at 0.4 kPa oxygen in RD cortex. AlaAT confirmed to be a gene highly sensitive to the oxygen levels, also showing different expression patterns in relation to the timing of oxygen shift application. The possible modulation of sucrose metabolism and glycolysis in relation to the hypoxic conditions applied and the storage protocol will be discussed, also considering the recovery mechanisms activated by the apple cortex tissue after different hypoxic stress conditions.

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