Preharvest GA3 treatment at optimized time points enhanced the storability of 'Shixia' longan fruit

The effects of 50 mg L-1 GA3 spraying at 65+75 days after flowering (DAF) (GA3_a), 75+85 DAF (GA3_b) and 85+95 DAF (GA3_c) on the room-temperature storability were compared to screen the ideal treatment timepoints. GA3_b significantly inhibited the increasing of mass loss, rotting, aril breakdown, electrolyte leakage and pericarp browning. More importantly, GA3_b enhanced ROS-scavenging capacity through up-regulating activities of PAL (phenylalanine ammonia-lyase), CAT (catalase) and APX (ascorbate peroxidase), therefore reduced H2O2 and malondialdehyde, retained phenolics, chlorophylls and carotenoid in pericarp at the later storage stages. GA3_b significantly inhibited pericarp enzymatic-browning by down-regulating expression and activities of POD (peroxidase), PPO (polyphenol oxidase) and LAC (laccase) and postharvest flavan-3-ols' polymerization. Moreover, GA3_b up-regulated GA3, SA and MeJA content at ripening & earlier storage, inhibited ABA biosynthesis at 85 DAF, up-regulated postharvest expression of NCED (9-cis-epoxycarotenoid dioxygenase), ABF (Abscisic acid-insensitive 5-like protein), NPR1 (non-expresser of pathogenesis related [PR] 1) expression but down-regulated PR1 (pathogen-related protein 1) and might promote survival of pericarp cell. In summary, 50 mg L-1 GA3 spraying at 75+85 DAF was an ideal treatment to effectively improved the storability of longan fruit through enhancing ROS-scavenging capacity, inhibiting enzymatic-browning and promoting the survival of pericarp cell by reprogramming phytohormone.