Regulation of Embden-Meyerhof-Parnas (EMP) Pathway and Tricarboxylic Acid (TCA) Cycle Concerning Aberrant Chilling Injury Behavior in Postharvest Papaya (Carica papaya L.)

Postharvest abnormal chilling injury (CI) behavior in papaya (Carica papaya L.) fruit is a rare phenomenon that may be associated with respiratory metabolism. This study thus aimed to investigate the impacts of storage temperatures (1 and 6 degrees C) on the respiratory metabolism of postharvest papaya and its impact on CI development. Results demonstrated that 1 degrees C storage reduced the activities of hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), citrate synthase (CS), and alpha-ketoglutarate dehydrogenase (alpha-KGDH) and regulated the expression of corre-sponding enzymes in the Embden-Meyerhof-Parnas (EMP) pathway and tricarboxylic acid (TCA) cycle compared with 6 degrees C storage, resulting in a lower respiration rate of the EMP-TCA pathway and mitigating the development of CI. Meanwhile, lower contents of nicotinamide adenine dinucleotide (hydrogen) (NAD(H)) were observed in papaya fruit stored at 1 degrees C. Notably, papaya fruit stored at 1 degrees C maintained higher activity and transcriptional levels of SDH and IDH during the whole storage period. These findings suggest that 1 degrees C storage reduced the respiration rate of the EMP-TCA pathway by reducing the expression level and activity of related enzymes, which is conducive to the reduction of respiration substrate consumption and finally alleviating the occurrence of CI.

Automated summary

Storage temperature has an impact on the respiratory metabolism and development of abnormal chilling injury in papaya. Storage at 1 degree Celsius reduces the respiration rate of the EMP-TCA pathway, lowers the consumption of respiratory substrates, and mitigates the occurrence of chilling injury.