Green 'Anjou' pear and its bud mutation, red 'Anjou' were compared to understand their differences in phenolic metabolism and its effect on primary metabolism. In the flesh of the two cultivars, no difference was detected in the concentration of any phenolic compound, the transcript level of MYB10 or the transcript levels or activities of key enzymes involved in anthocyanin synthesis. Compared with green 'Anjou', the shaded peel of red 'Anjou' had higher anthocyanin concentrations, higher transcript levels of MYB10 and higher activity of UDP-glucose:flavonoid 3-O-glycosyltransferase (UFGT), suggesting that MYB10 regulates UFGT to control anthocyanin synthesis in red 'Anjou' peel. In the sun-exposed peel, activities of phenylalanine ammonia lyase, dihydroflavonol reductase, flavonol synthase and anthocyanidin synthase as well as UFGT were higher in red 'Anjou' than in green 'Anjou'. The peel of red 'Anjou' had higher activities of sorbitol dehydrogenase, raffinose synthase and sucrose synthase and higher levels of raffinose, myo-inositol and starch, indicating that sorbitol metabolism, raffinose synthesis and starch synthesis were upregulated in red 'Anjou'. The flesh of red 'Anjou' had higher concentrations of glucose, but lower activities of ATP-dependent phosphofructokinase, pyruvate kinase and glucose-6-phosphate dehydrogenase and lower dark respiration. The peel of red 'Anjou' had higher activities of glutaminase, asparagine synthetase and asparaginase, and higher concentrations of asparagine, aspartate, alanine, valine, threonine and isoleucine. The effects of anthocyanin synthesis on primary metabolism in fruit peel are discussed.
European pears (Pyrus communis L.) require a range of cold-temperature exposure to induce ethylene biosynthesis and fruit ripening. Physiological and hormonal responses to cold temperature storage in pear have been well characterized, but the molecular underpinnings of these phenomena remain unclear. An established low-temperature conditioning model was used to induce ripening of ‘D’Anjou’ and ‘Bartlett’ pear cultivars and quantify the expression of key genes representing ripening-related metabolic pathways in comparison to non-conditioned fruit. Physiological indicators of pear ripening were recorded, and fruit peel tissue sampled in parallel, during the cold-conditioning and ripening time-course experiment to correlate gene expression to ontogeny. Two complementary approaches, Nonparametric Multi-Dimensional Scaling and efficiency-corrected 2-(ΔΔCt), were used to identify genes exhibiting the most variability in expression. Interestingly, the enhanced alternative oxidase (AOX) transcript abundance at the pre-climacteric stage in ‘Bartlett’ and ‘D’Anjou’ at the peak of the conditioning treatments suggests that AOX may play a key and a novel role in the achievement of ripening competency. There were indications that cold-sensing and signaling elements from ABA and auxin pathways modulate the S1-S2 ethylene transition in European pears, and that the S1-S2 ethylene biosynthesis transition is more pronounced in ‘Bartlett’ as compared to ‘D’Anjou’ pear. This information has implications in preventing post-harvest losses of this important crop.
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