Changes in antioxidant properties and their relationship to paclobutrazol-induced flooding tolerance in Welsh onion

BACKGROUND: Flooding is an important factor affecting Welsh onion production, because under such stress the production and quenching of reactive oxygen species (ROS) in plants will fail to be kept in a balanced state. The purpose of this study was to examine the effect of paclobutrazol (PBZ) on the growth and development of Welsh onion plants (Allium fistulosum L.), particularly to evaluate changes in antioxidant properties. RESULTS: Welsh onion plants were treated with 0 and 2 ppm per plant of PBZ, subsequently subjected to non-flooding and flooding-stress conditions for 0, 1, 5, 9 and 13 days, followed by a 4-day drainage period. Flooding stress was judged by any decrease in biomass production and chlorophyll content. The results indicated that PBZ applied to plants was able to protect Welsh onion from flooding stress. The increased levels of antioxidant activity in different systems, including alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH)-radical scavenging activity, superoxide anion radical scavenging, metal chelating activities and reducing power observed on flooding, afforded the Welsh onion improved flooding tolerance. Under non-flooding conditions, the antioxidative activity of Welsh onion was regulated and elevated by PBZ pretreatment. CONCLUSION: It seems that the PBZ-induced flooding tolerance of Welsh onion is mediated through increased activities of various antioxidative systems. Thus, pre-applying 2 ppm per plant of PBZ 24 h prior to flooding could mitigate flooding stress. (C) 2008 Society of Chemical Industry.