Enhancement of respiratory metabolism of the pentose phosphate pathway (PPP) strengthens the chilling tolerance of postharvest papaya fruit stored at 1 °C

Papaya (Carica papaya L.) is a typical tropical fruit with high economic value but relatively sensitive to cold temperatures and vulnerable to chilling injury (CI). Low storage temperatures result in more severe CI symptoms in most tropical fruits and vegetables. Notably, papaya fruit stored at 1 degrees C exhibit lesser CI symptoms than those stored at 6 degrees C. The variance in the severity of CI and respiration metabolism in papaya fruit when stored at both temperatures was thus investigated to explicitly explain the mechanism of the abnormal CI phenomenon of papaya fruit. Papaya fruit stored at 1 degrees C had a significant decrease in the development of CI compared to fruit stored at 6 degrees C. Fruit stored at 1 degrees C were also accompanied by an increase in the respiration rate of the pentose phosphate pathway (PPP) and nicotinamide adenine dinucleotide phosphate (NADPH) content and lower pro-duction of the reactive oxygen species (ROS). Storage at 1 degrees C also remarkably promoted the activities of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) and upregulated the expression of CpG6PDH and Cp6PGDH genes compared to storage at 6 degrees C. These results suggest that enhancing the respiratory metabolism of the PPP improves the ability to scavenge ROS by increasing the content of NADPH, which consequently strengthens the chilling tolerance of postharvest papaya fruit stored at 1 degrees C.

Automated summary

Papaya fruit stored at 1 degrees C exhibits milder chilling injury symptoms and has stronger respiratory metabolism and chilling tolerance compared to fruit stored at 6 degrees C.