Seasonal changes in glutamate dehydrogenase activities and amino acid content in green asparagus during spear growth

Seasonal changes in glutamate dehydrogenase (GDH) amination and deamination activities in the top and bottom portion of the spear of two asparagus cultivars 'Welcome' and 'E414' grown in greenhouse conditions from March to October were investigated. In the two cultivars and portions, GDH amination activity showed an increasing trend in July, then declined remarkably from August to September and started to increase in October. On the other hand, GDH deamination activity increased gradually with the temperature changes during growth of the spears. GDH deamination activity in the top portion showed significantly higher activity than in the bottom portion. Of the two cultivars, 'Welcome' had relatively higher activities in both GDH amination and deamination activities than 'E414' in both portions, but differences were not significant. The GDH activities had significantly higher activities in the top portion than in the bottom portion. Glutamine, glutamic acid, asparagine and aspartic acid contents fluctuated during the growing season with a higher content at higher temperature and lower content at low temperature. These results clearly demonstrate that temperature had a significant influence on the metabolic rate of enzymes and its accumulation of amino acid in asparagus spears.