Low Temperature and Breaking of Dormancy Effects on Respiration Rate, Sugars, Phenolics and Peroxidase Activity Changes in Inner Buds of Onion Allium cepa L.

Respiration rate (CO 2 production), soluble sugars, total phenolics and peroxidase activity (POD) were measured in inner bud tissues during the break of dormancy of onion bulbs treated for one week at 0°C and stored in the dark at 20°C. Results showed that after eight weeks, the RR C O 2 of sprouted control onions was 52% higher than that of unsprouted control onions. High concentrations of soluble sugars (glucose, fructose and sucrose) were observed for cold treated bulbs (from 9 to 20 mg g - 1 FW) after two weeks following cooling, but in control bulbs high concentrations were only observed after eight weeks. In cold-treated onions, a slight increase in phenolics (from 0.17 to 0.2 mg g - 1 FW) was observed after one week, and then there was a decrease to 0.12 mg g - 1 FW after five weeks. In inner buds of control bulbs, an increase from 0.17 to 0.2 mg g - 1 FW was observed during the first five weeks and then a decrease to 0.15 mg occurred during the three last weeks when the bulbs began to sprout. Peroxidase activity followed the same pattern as phenolics, with a decrease (38%) in cold-treated bulb after four weeks. In control samples, a decrease of 25% was noted after eight weeks. This decrease in POD activity coincided with the decrease in phenolics and the onset of sprouting. With cold treatment, total sprouting was observed after eight weeks. In comparison, only 20% of the control bulbs started sprouting after the same period.