Regulation on Antioxidant Defense System in Rice Seedlings (Oryza sativa L. ssp. indica cv. ‘Pathumthani 1’) Under Salt Stress by Paclobutrazol Foliar Application

The present study investigated the effect of paclobutrazol (PBZ) foliar application on oxidative metabolism in salt-stressed rice (Oryza sativa L. cv. ‘Pathumthani 1’; PTT1) seedlings. Fourteen-days-old rice seedlings, grown in the pots were pretreated with 15 mg L-1 paclobutrazol supplied as foliar spray. One week after pretreatment, the rice seedlings were exposed to salt stress (150 mM NaCl) for 12 days. It was observed that salinity enhanced the production of reactive oxygen species (ROS), including superoxide radical (O2•−), hydrogen peroxide (H2O2) and hydroxyl radical (OH·). It also increased reactive oxygen species-associated oxidative damage, measured in terms of lipoxygenase activity, conjugated dienes, malondialdehyde content and relative electrolyte leakage. Increase in these parameters was associated with the decrease in the activity of enzymatic antioxidants [superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT)] and the levels of non-enzymatic antioxidants [ascorbic acid (AsA), total glutathione and α-tocopherol contents). Pretreatment of seedlings with paclobutrazol significantly lowered reactive oxygen species accumulation and membrane damage (p < 0.05), which can be correlated with the increased antioxidant activity (both enzymatic and non-enzymatic traits) under salt stress. The study concluded that paclobutrazol-treatment up-regulates the antioxidant defense system and recuperates the salt-induced oxidative damage in ‘Pathumthani 1’ rice seedlings under salt stress

Reduction of enzymatic browning of harvested 'Daw' longan exocarp by sodium chlorite

ABSTRACT: Post-harvest exocarp browning is a major problem resulting in reduced shelf-life of longan fruits. The objective of this study was to evaluate the possibility of using sodium chlorite (SC) as an anti-browning agent for controlling enzymatic browning of harvested longan fruits during storage at ambient conditions. Longan fruits cv. Daw were dipped in 0.001%, 0.005%, 0.01%, and 0.05% SC (W/V) for 10 min. The fruits were packed in cardboard boxes and stored at 25 ± 1°C with a relative humidity of 82 ± 5% for 72 h. Changes in browning index, colour parameter (L* and b* values), polyphenol oxidase (PPO) activity, peroxidase (POD) activity, and total phenolic content were measured. The results showed that the fruits treated with SC had lower browning index, but higher L* (lightness) and b*(yellowness) values than those of the control group during storage for 48 h. SC at a concentration of 0.01% was the most effective in reducing exocarp browning. The application of SC reduced PPO and POD activities and delayed a decrease in the total phenolic content. The treatment with 0.01% and 0.05% SC had the lowest PPO and POD activities, and maintained the highest total phenolic content. It was concluded that an application of SC is an alternative method for reducing exocarp browning and maintaining quality of harvested longan fruits