Ascorbic acid mitigates ROS-induced chilling injury development in postharvest sweet basil via improving antioxidant defense system to impede senescence process

The visible manifestations of chilling injury symptoms significantly worsen nutritional and quality losses in sweet basil, rendering low-temperature storage impractical for extending its postharvest longevity. This study sought to determine how immersion in ascorbic acid (AsA) affected the visible development of chilling injury symptoms (leaf discoloration and death lesion manipulation) in sweet basil leaves, specifically focusing on oxidative damage, chlorophyll degradation and cell death. After being submerged in AsA at concentrations of 0, 1, 5 and 10 mM for 20 min, sweet basil branches were kept at 6 +/- 1 degrees C for 12 d. The best concentration (10 mM) in alleviating chilling injury development and maintaining leaf quality was underwent analysis for reactive oxygen species (ROS) accumulations, antioxidant systems, chlorophyll degradation and cell death. The visible sight of chilling injury initially appeared on day 3 coinciding with gradually elevated levels of ROS (superoxide and hydrogen peroxide), malondialdehyde and caspase 3, 8 and 9-like activities. Moreover, a surging in leaf discoloration coincided with the reduction in the rate of electron transport in isolated chloroplast and chlorophyll contents. However, the AsA-treated group exhibited lower chilling injury (25-60 %) than control on day 3 to day 12, which was associated with enhanced antioxidant systems, decreased ROS accumulation and lower activities of chlorophyll degrading enzymes (chlorophyll peroxidase and chlorophyllase) as well as caspase-like activities. These findings suggested that AsA immersion elevated antioxidant activity to suppress oxidative damage, reduced chlorophyll degradation and mitigated cell death, thereby improving cold stress tolerance in sweet basil during storage.