Abstract: In order to investigate the change in proline metabolism of two varieties of Hami melon fruits during low-temperature storage, ‘Xizhoumi 25’ and ‘Gashi’ melons were pre-cooled for 24 h and then placed for up to 42 days in a mechanical cold storage at (3.0 ± 0.5) ℃. Chilling injury symptoms were recorded, and chilling injury index, free proline content and proline metabolism-related indexes were measured every seven days . The results showed that the symptoms of chilling injury in ‘Gashi’ melon were significantly milder than those in ‘Xizhoumi 25’ melon, and as the storage time increased, free proline content, Δ1-pyrrolidine-5-carboxylic acid synthase (P5CS) activity, ornithine transaminase (OAT) activity and their relative gene expression increased significantly for both varieties; all these indicators were significantly higher in ‘Gashi’ melon than ‘Xizhoumi 25’ melon. The activity and relative gene expression of proline dehydrogenase (ProDH) decreased, indicating that both varieties of Hami melon fruits could resist chilling injury by increasing the free proline content and the activities of P5CS and OAT, the key enzymes for proline synthesis, and decreasing the activity of ProDH, the key enzyme for proline degradation. The metabolomics study revealed that the amino acid content of ‘Xizhoumi 25’melon decreased when the chilling injury became more serious, while the amino acid content of ‘Gashi’ melon showed an opposite trend. Whole gene synthesis of CmP5CS, a key enzyme gene involved in the proline metabolic pathway of Hami melon fruits, revealed that the Hami melon CmP5CS gene had the closest relatedness to melon (LOC103485529) P5CS, indicating functional similarity between them.

Key words: Hami melon; chilling injury; proline metabolism; metabolomics; whole gene synthesis