Changes in the Activities of Glutamine Synthetase and Glutamate Dehydrogenase of Asparagus Spears after Harvest

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Respiration rate, glutamine/glutamic acid levels and the activities of glutamine synthetase (GS, EC 6.3.1.2) and glutamate dehydrogenase (GDH, EC 1.4.1.2) in the top and bottom portions of harvested asparagus spears (<I>Asparagus officinalis</I> L. cv. Welcome) were examined. Spears were stored for up to 5 days at 25°C. Respiration rate (CO<SUB>2</SUB> production) of the spears declined during the first 2 days of storage and increased subsequently until the end of the storage period. The respiration rate of the top portion was over 2 or 3 times greater than that of the bottom portion or intact spears. GS activity increased in the top and bottom portions of the spears after 1 day and declined to about 38% and 65% of the initial levels by day 5, respectively. GDH activities in the top portion as well as the bottom portion showed an increasing trend until the end of the storage. Glutamine level increased, whereas glutamic acid decreased in concentration substantially during the first 24 h after harvest, in the top and bottom portions of the spears. There was a highly significant negative correlation observed between GS activity and the glutamine and glutamic acid content in the top and bottom portions of the spears. On the other hand, a highly significant positive correlation between GDH activity and the glutamine and glutamic acid content in the top and bottom portions of the spears was observed.