Enhanced cyanide-resistant respiration as the predominant respiratory metabolic pathway in abnormal chilling injury behavior of postharvest papaya

Abstract

An increasing number of studies have demonstrated that reactive oxygen species (ROS) play a crucial role in the chilling injury (CI) of postharvest fruit and vegetables. This is not only associated with the free radical scavenging system but is also intimately connected to the electron transport chain pathway. However, it remains unclear whether ROS is associated with the electron transport chain in the abnormal chilling behavior observed in postharvest papaya. As such, this study investigated the electron transport chain of papaya fruit stored at 1 ℃ and 6 ℃ and its connection to ROS. In comparison to storage at 6 ℃, storage at 1 ℃ suppressed the expression of CpCCO, and induced the upregulation of CpAOX expression in papaya fruit. Throughout the middle and late stages of storage, there was an increase in pyruvate content and ubiquinone reduction level. The increase had two effects: it inhibited cytochrome oxidase (CCO) activity and promoted alternative oxidase (AOX) activity, leading to a blocked cytochrome pathway and an increased proportion of cyanide-resistant respiratory pathways. Consequently, the cyanide-resistant respiratory pathway supplanted the cytochrome pathway as the primary electron transport pathway. This transition effectively curbed the accumulation of ROS, thereby diminishing the damage degree of fruit cell membrane, boosting chilling tolerance, and ultimately inhibiting the CI of papaya fruit, which led to the emergence of abnormal chilling injury.