Quantitative changes of free amino acids and amides in barley plants during ammonia and nitrate assimilation

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Quantitative changes of free amino acids and amides were investigated in barley plants supplied with ammonia or nitrate for 1 hr, followed by transfer to nitrogen-deficient medium for 6 hr. Changes in levels of free ammonia and nitrate were closely correlated with the synthesis of amino acids and amides. In ammonia-supplied roots, rapid primary synthesis and turnover of glutamine and glutamate occurred, with glutamine playing a leading role in the assimilation. Decreases of glutamate and aspartate during the initial period suggested that glutamate was synthesized more slowly than glutamine, and the aspartate-glutamate cycle was in operation. After transfer to N-deficient medium, glutamine was rapidly converted into glutamate, which in turn seemed to undergo transamination to aspartate and alanine. There was also a rapid rise in O_2-uptake of roots during the 1 hr supply of ammonia. In nitrate-supplied plants, most of the absorbed nitrate was transported to the shoot where it was assimilated into glutamate and aspartate. The amount of glutamine increased continuously, suggesting that it was a primary product of nitrate assimilation In roots. The crucial difference observed between synthesis rates of amino compounds during the initial periods of the two treatments was probably due to a lag in nitrate reduction. We will discuss metabolic phenomena associated with active assimilation of ammonia.
日本植物生理学会の論文