Role of CaCl2 in nitrate assimilation in leaves and roots of tobacco plants (Nicotiana tabacum L)

The aim of this study was to determine the response of NO; assimilation in roots and leaves to different CaCl2 application (T1, 1.25 mM CaCl2. 2H(2)O; T2, 2.5 mM CaCl2. 2H(2)O and T3, 5 mM CaCl2. 2H(2)O). Tobacco plants (Nico tiana tabacum cv Sevilla) were grown under controlled conditions and submit ted to regular fertilization with macro- and micronutrients. The content of Ca2+, Cl- and NO3- the activity of the enzymes related to the process of N O3- reduction (NR: nitrate reductase, EC 1.6.6.1; NiR: nitrite reductase, E C 1.7.7.1; GS: glutamine synthetase, EC 6.3.1.2; GOGAT: glutamate synthase, EC 1.4.1.14; PEPC: phosphoenolpyruvate carboxylase, EC 4.1.1.31), and the end products of this process (amino acids and proteins) were analysed in ro ots and leaves. Our results indicate that the utilization of NO3- in the pl ant was influenced by the different treatments. NO3- was translocated towar ds the aerial part and subsequently assimilated in the leaves in treatments T1 and T2, the latter significantly intensifying these processes and givin g rise to greater production of dry matter both in the leaves and in the ro ots. With the T3 treatment, NO3- assimilation occurred principally in the r oots, due possibly to decreased NO3- translocation towards the aerial part, thereby increasing its availability in the roots. In addition, the possibl e negative effect of the maximum foliar concentrations of Ca2+ and Cl- on t he foliar activity of NR in this treatment could also cause NO3- assimilati on in the roots with the T3 treatment. Finally, it is noteworthy that the a pplication of T3 significantly reduced root growth. (C) 1999 Elsevier Scien ce Ireland Ltd. All rights reserved.