Abstract
Tobacco plant was grown for 40 days hydroponically in nutrient solutions composed of different forms of nitrogen, like NO$_3$$^{[-10]}$ -N, NH$_4$$^{＋}$-N, and a mixed formulation of NO$_3$$^{[-10]}$ -N and NH$_4$$^{＋}$-N. Uptake response, nitrate reductase, and glutamine synthetase activity at growth stage were investigated to understand the basic knowledge of nitrogen metabolism. The better growth of shoot and root was observed in the mixed nutrient solution than NO$_3$$^{[-10]}$ -N or NH$_4$$^{＋}$-N, alone. The plant growth in NH$_4$$^{＋}$-N nutrient solution was poor due to ammonium toxicity. The pH of nutrient solution containing NO$_3$$^{[-10]}$ -N increased up to 40 days after transplanting. But the pH of solution containing NO$_3$$^{[-10]}$ -N decreased drastically to 3.42 at 20 days after transplant. The pH in the mixed formulation dropped to pH 3.64 at 30 days after transplant and showed re-increase. It is assumed that nitrogen of NH$_4$$^{＋}$-N form was taken up preferentially at early stage and NO$_3$$^{[-10]}$ -N form was taken up preferentially at middle stage in the treatment with the mixed solution. The result indicates that the relative proportion of nitrogen forms affected the uptake patterns at each growth stages. The contents of chlorophyll and soluble protein were high with the mixed solution. Total nitrogen content was the highest in NH$_4$$^{＋}$-N solution and the content also increased by the application of the mixed type of nitrogen. The amount of nitrate in leaves was high in NO$_3$$^{[-10]}$ -N treatment and the amount of ammonium was high in NH$_4$$^{＋}$-N treatment. The activity of nitrate reductase or glutamine synthetase was highest in the leaves grown in mixed nutrient solution than in those with any other single of nitrogen form.
질소의 형태를 질산태(NO$_3$$^{-}$-N), 암모니아태(NH$_4$$^{＋}$-N) 그리고 질산태와 암모니아태(NO$_3$$^{-}$-N ＋ NH$_4$$^{＋}$-N)를 혼합한 양액 하에서 수경재배하여 담배의 생육단계별 질소이용에 따른 흡수 양상과 생육 및 nitrate reductase, glutamine synthetase 효소활성을 평가하여 질소 시비 유형에 따른 체내 질소대사의 기초자료를 제공하고져 축행한 결과는 다음과 같다. 질소의 형태별 생육은 NO$_3$$^{-}$-N, NH$_4$$^{＋}$-N 단독 처리구보다 혼합처리구에서 지상 및 지하부의 생육이 좋았고, NH$_4$$^{＋}$-N 처리구에서는 암모늄 독성에 의해 생육이 극히 불량하였다. 생육단계별 양액의 pH 변화는 NO$_3$$^{-}$-N 처리구에서 이식 초기부터 이식 후 40일까지 증가하였고 NH$_4$$^{＋}$-N 처리구에서는 이식 후 20일에 pH 3.42, 혼합처리구에서는 이식 후 30일에 pH 3.64까지 떨어졌다가 증가하였다. 혼합처리구의 질소흡수반응은 생육초기에서는 NH$_4$$^{＋}$-N의 흡수를 우선하고 생육중기부터 NO$_3$$^{-}$-N 흡수가 증가하여 흡수 양상을 달리하였다. 생육시기에 따라 흡수형태도 NO$_3$$^{-}$-N와 NH$_4$$^{＋}$-N 사이의 상대적인 비율에 의해 크게 영향을 미쳤다. 엽록소와 가용성 단백질은 혼합처리구에서 전질소는 NH$_4$$^{＋}$-N 처리구에서 높았고, 특히 NH$_4$$^{＋}$-N 질소를 시비하였을 때는 질소함량이 증가하였다. 질산함량이 증가하였다. 질산함량은 NO$_3$$^{-}$-N 처리구에서 암모니아함량은 NH$_4$$^{＋}$-N 처리구에서 높았고, 산소 활성은 혼합처리구에서 nitrate reductase와 glutamine synthetase 활성이 높았다.
