NITROGEN-METABOLISM IN TOBACCO PLANTS (NICOTIANA-TABACUM L.) - ROLE OF BORON AS A POSSIBLE REGULATORY FACTOR

Tobacco plants (Nicotiana tabacum cv. Sevilla) were grown under contro lled conditions and submitted to regular fertilization with macro- and micronutrients. The aim of the experiment was to determine the respon se of NO3- assimilation to four different boron (B) doses (B1: 0.5 mu M H3BO3; B2: 5 mu M; B3: 10 mu M H3BO3; and B4: 20 mu M H3BO3). The co ntent of foliar B and NO3-, the activity of the enzymes related to the process of NO3- reduction (NR, NiR, GS, GOGAT, and PEPC), and the end products of this process (amino acids and proteins) were analyzed. Ou r results indicate a positive effect of the B on its concentration in leaves and on NO3- assimilation, possibly by an activation of the enzy matic proteins involved in this process. Boron addition significantly reduced the foliar NO3- concentration. Finally, B affected plant growt h, since an increase in leaf dry weight and in the content of proteins and amino acids was shown.