Ethylene formation in tobacco leaf stimulated by sodium bicarbonate treatment
Sodium bicarbonate is effective in accelerating leaf senescence and in stimulating nicotine demethylation in tobacco. It also showed potential as a color developing agent during curing of burley tobacco and in the early identification of nicotine to nornicotine converter plants. Experiments were done to determine the effect of sodium bicarbonate on stimulating endogenous ethylene production. Gas chromatography was used to measure the ethylene evolution on tobacco leaf disks in sealed containers. Ethylene levels increased rapidly during the first 4 hours after the application of 1% aqueous sodium bicarbonate solution, and remained high during the subsequent 20 hours, and then gradually decreased. When sodium bicarbonate treatment was compared to the control (water treatment), ethylene levels were found to be 62.8% to 172.9% higher during the first 6 hours, and stayed higher than the control for 72 hours. The rate of ethylene production was determined by sealing leaf disks in the container for 30 minutes before each measurement and air-curing them at 35 °C and 80% RH. The ethylene generation rate was the highest from 4 to 24 hours after the treatment, and remained constant for the subsequent 48 hours. Incubation at 35 °C of sodium bicarbonate-treated leaves gave 30% to 77% higher ethylene levels than when incubated at room temperature (24 °C) during the first 24 hours. Increasing the sodium bicarbonate concentration (0 to 2%) significantly enhanced ethylene production. Incubation of sodium bicarbonate-treated leaf with ethylene inhibitor aminoethoxyvinylglycine (10-4M) reversed the stimulation of ethylene production and the yellowing of lamina. Therefore, our results indicate that the stimulation of tobacco leaf senescence and nicotine demethylation by sodium bicarbonate may be due to its effect on ethylene generation.