Role of CaCl2 in Ammonium Assimilation in Roots of Tobacco Plants (Nicotiana tabacum L.)

The aim of this study was to determine the response of NH4+ assimilation in roots to different CaCl2 application (Ca1: 1.25 mmol/L CaCl2 · 2H2O, Ca2: 2.5 mmol/L CaCl2 · 2H2O and Ca3: 5 mmol/L CaCh · 2H2O). Tobacco plants (Nicotiana tabacum cv. Tennessee 86) were grown under controlled conditions and submitted to regular fertilization with macro- and micronutrients. The contents of Ca2+, Cl- and NH4+, the activity of enzymes related to the process of NH4+ assimilation (GS: glutamine synthetase, EC 6.3.1.2.; GOGAT: glutamate synthase, EC 1.4.1.14; GDH, glutamate dehydrogenase EC 1.4.1.2.), and the end products of this process (amino acids and proteins) were analysed in roots. Our results indicate that the utilization of NH4+ in the plant was influenced by the different treatments. In the Ca3 treatment the NH4+ content was lower than in Ca1 and Ca2, apparently due to the higher GS, GOGAT and GDH activities registered in Ca3. However, we found that the concentration of amino acids and protein as well as biomass production in the root was more important in the Ca1 and Ca2 treatments than in Ca3. This is the result of the greater translocation of these products to the shoot, stimulated by the high Ca2+ dosage applied (5 mmol/L) to the cultivation medium in the Ca3 treatment.