Role of CaCl 2 in nitrate assimilation in leaves and roots of tobacco plants ( Nicotiana tabacum L.)

Abstract

The aim of this study was to determine the response of NO 3 − assimilation in roots and leaves to different CaCl 2 application (T1, 1.25 mM CaCl 2·2H 2O; T2, 2.5 mM CaCl 2·2H 2O and T3, 5 mM CaCl 2·2H 2O). Tobacco plants ( Nicotiana tabacum cv Sevilla) were grown under controlled conditions and submitted to regular fertilization with macro- and micronutrients. The content of Ca 2+, Cl − and NO 3 −, the activity of the enzymes related to the process of NO 3 − reduction (NR: nitrate reductase, EC 1.6.6.1; NiR: nitrite reductase, EC 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 roots and leaves. Our results indicate that the utilization of NO 3 − in the plant was influenced by the different treatments. NO 3 − was translocated towards the aerial part and subsequently assimilated in the leaves in treatments T1 and T2, the latter significantly intensifying these processes and giving rise to greater production of dry matter both in the leaves and in the roots. With the T3 treatment, NO 3 − assimilation occurred principally in the roots, due possibly to decreased NO 3 − translocation towards the aerial part, thereby increasing its availability in the roots. In addition, the possible negative effect of the maximum foliar concentrations of Ca 2+ and Cl − on the foliar activity of NR in this treatment could also cause NO 3 − assimilation in the roots with the T3 treatment. Finally, it is noteworthy that the application of T3 significantly reduced root growth.