Effects Of Sucrose On The Activities Of Enzymes Involved In Ammonium Assimilation In Roots Of Rice (Oryza Sativa L.) Cultivated In Different Nitrogen Source

Sugar, organic acid and amino acids have important effects on gene expression and enzyme activities involved in carbon and nitrogen metabolism. With rice cultivating, sucrose was fed to the nutrient solution containing (NH₄)₂SO₄ (NH₄⁺) or L-Ala, and then determined the activities of glutamine synthetase(GS), NADH-dependent glutamate synthase(NADH-GOGAT), phosphoenolpyruvate carboxylase(PEPC), NADP-dependent isocitrate dehydrogenase(NADP-ICDH), and NADH-dependent glutamate dehydrogenase(NADH-GDH). The results showed that sucrose induced markedly the enzyme activities of GS and NADH-GOGAT in roots of seedlings with NH₄⁺ as the nitrogen source ,however, inhibited them in roots of seedlings growing in L-Ala nitrogen source. Sucrose had different effects on the activity changes of PEPC, NADH-ICDH and NADH-GDH. Without sucrose supplementation, the activities of GS, NADH-GOGAT, PEPC, NADP-ICDH in the roots of rice seedlings growing in L-Ala nitrogen source were higher than that with NH₄⁺ as the nitrogen source. The changes trend in biomass and protein content were coincident with the former parameters. Different concentration sucrose was fed to the seedlings grown in (NH₄)SO₄ nutrient solution, the results followed. From 24h to 48h, the activity of GS, NADH-GOGAT, NADP-ICDH, the soluble protein content and biomass increased gradually, and their values have a positive correlation with sucrose concentration; to 72h, the enzyme activity of GS began to fall down when the sucrose concentration was 0.5% and 2%, but continued to increase when the sucrose concentration was 0.1%. The enzyme activity of NADH-GOGAT maintained to increase when the sucrose concentration was 0.1% and 0.5%, only decreased when the sucrose concentration was 2%. The enzyme activity of NADP-ICDH, biomass and the soluble protein content continued to increase under three different sucrose concentration. The enzyme activity of NADH-GDH maintained to decrease at three sampled time at every sucrose concentration. For NADH-PEPc, the enzyme activity maintained to increase from 24h to 72h when the sucrose concentration was 0.1%, had a decrease at 72h when the concentration was 0.5% and 2%. Based on the additional carbon skeleton of Ala compared to (NH₄)SO₄, these resulted suggested that carbon/nitrogen balance play a important role in the different regulation of the enzyme activity.