Emission of volatile esters and transcription of ethylene- and aroma-related genes during ripening of 'Pingxiangli' pear fruit (Pyrus ussuriensis Maxim)

- We analyzed biochemical and physiological changes during 'Pingxiangli' pear ripening.
- Aldehyde levels decreased and ester levels increased during fruit ripening.
- Ethylene may regulate ester formation in climacteric pear fruit.
- Increased ester production coincided with the ethylene peak during fruit ripening.
- Expression of LOX, ADH, and AAT genes may be critical for ester production.

The fruit of Pyrus ussuriensis Maxim produces an intense aroma, which is accompanied by elevated ethylene levels, during postharvest ripening. In this study, we evaluated the relationships between lipoxygenase (LOX) pathway-derived volatiles and the transcription of genes related to ethylene and ester biosynthesis during fruit ripening. The amount of esters produced by the fruit increased dramatically during ripening, while the amount of aldehydes decreased. During the 12-day ripening period, the transcript levels of PuACO2 and PuACO3 peaked on day 6, and then remained constant. The transcript levels of PuACO5 and PuACO6 peaked on day 6 and day 3, respectively, and subsequently decreased throughout the ripening period. PuLOX6 and PuLOX11 showed increased transcript levels as the fruit ripened, while the transcript levels of PuLOX1 and PuLOX8 peaked on day 3. The highest transcript levels of PuADH2, PuADH3, and PuADH5 were detected on day 6, day 3, and day 1, respectively, during the 12-day ripening period. The transcript levels of PuAAT first increased, and then decreased during ripening. Climacteric increases in ethylene production and volatile ester concentrations were observed during the ripening of P. ussuriensis, and PuLOX1, PuLOX8, PuADH3 and PuAAT may play important roles in ester formation.