Fluctuations in the Activities of Some Ammonia-assimilating Enzymes and Ammonia Content in Broccoli Harvested at Different Seasons

Temperature changes during growth and development influence various metabolic processes in plants. To determine its influence in broccoli (Brassica oleracea L.) at harvest, we examined the activities of some ammonia-assimilating enzymes and ammonia content in the floret and branchlet portions of two cultivars (Hartland and Sairin) harvested from October to April. Glutamine synthetase (GS; EC 6.3.1.2) in the two portions showed decreasing and increasing activity in the florets and branchlets, respectively with decrease in temperature. Asparagine synthetase (AS; EC 6.3.5.4) activity did not show significant variation in both cultivars throughout the experimental period except the branchlet portion wherein activity reached a peak in January and then fluctuated until April. AS activity was significantly higher in the floret than in the branchlet portion in both cultivars. Glutamate dehydrogenase (GDH; EC 1.4.1.2) aminating activity was higher during warmer harvest months while no distinct declining or inclining trend was found in the deaminating activity throughout the experimental period. GDH activities were significantly higher in the branchlet than in the floret portion except for GDH-amination in Hartland harvested in October and December. In the floret portion GDH activity was not detected in Sairin and Hartland after December and February harvests, respectively. The results of this study may provide insights in obtaining optimum yield and product quality of broccoli.