Effects of Sucrose on the Activities of Enzymes Involved in Ammonium Assimilation in Roots of Rice Cultivated in Different Nitrogen Source

Sugar,organic acid and amino acids play important effects on gene expression and enzyme activities involved in carbon and nitrogen metabolism.With rice cultivating,sucrose was superinduced to the nutrient solution containing(NH₄)₂SO₄(NH₄⁺) or L-Ala,which contained same nitrogen content,and then determined the activities of glutamine synthetase (GS),NADH-dependent glutamate synthase(NADH-GOGAT),phosphoenolpyruvate carboxylase(PEPC),NADP-dependent isocitrate dehydrogenase(NADP-ICDH).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 and NADH-ICDH.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.Based on the additional carbon skeleton of Ala compared to(NH₄)₂SO₄,these resulted suggested that carbon/nitrogen balance play an important role in the different regulation of the enzyme activity.