Amelioration of nitrosative stress to reduce pericarp browning of harvested longan by chlorine dioxide

Abstract

Reactive nitrogen species (RNS) play a crucial role for plants to respond to environmental fluctuations. High formation of RNS leads to nitrosative stress and disorders in the higher plant. The use of gaseous chlorine dioxide (ClO2) treatments for postharvest application has grown in recent years due to its advantages over other methods, including its powerful antibrowning and antimicrobial activities and low environmental impacts. The purpose of this research was to determine the influence of ClO2 on RNS generation and nitrosative stress associated with browning of longan (Dimocarpus longan cv. Daw) pericarp after harvest. Longan were harvested and fumigated with ClO2 (0 and 10 mg L−1) for 10 min before being put in cardboard boxes and stored at 25±1°C for 7 d. The findings revealed that rapid pericarp browning was evident in the control at 6 h and the intensity increased steadily during storage. Browning developed in tandem with a significant rise in RNS levels (nitric oxide, nitrogen dioxide, peroxynitrite and S-nitrosoglutathione) and nitrosative stress (S-nitrosothiol, 3-nitrotyrosine, 8-nitroguanine and nitro fatty acid). Nitric oxide producing enzyme activities, including nitric oxide synthase (NOS) and nitrate reductase (NR), increased with a decline in their substrate contents (L-arginine and nitrate) and their product (L-citrulline and nitrite) and pH were also raised during severe pericarp browning. However, ClO2 fumigation reduced the activities of RNS producing enzymes and maintained their substrates for up to 5-6 d of storage. These reductions were correlated to lower RNS levels, nitrosative stress and pericarp browning, indicating that ClO2 treatment could diminish postharvest browning of ‘Daw' longan pericarp by lowering the activity of the RNS-producing enzyme, causes a reduction in RNS to counteract nitrosative stress.