While salinity effects have been largely documented in crop plants, little data are available on Nicotiana rustica species (snuff tobacco), mainly nitrogen metabolism changes. Here, tobacco (N. rustica L. var. Souffi) seedlings were grown for one month on control medium, and then exposed for seven days to different levels of salt stress (0, 50, 100 and 200 mM NaCl). A significant decrease in dry weight accumulation was observed only at 200 mM NaCl. Na+ and Cl- ions accumulation was greater in leaves relative to roots, while growth was similarly decreased in both organs. Referring to roots, leaf water content was less affected by salinity. The increase of endogenous levels of salt ions was accompanied by a drop in NO3-content in both leaves and roots, and a more pronounced decrease in K+ content in leaves. Under salinity, nitrate reductase activity (NR, EC 188.8.131.52) was inhibited in both leaves and roots. The activities of nitrite reductase (NiR, EC 184.108.40.206) and glutamine synthetase (GS, EC 220.127.116.11) were inhibited in leaves but not in roots by salt stress. In stressed seedlings, NH4+ contents, protease activity, aminating and deaminating activities of glutamate dehydrogenase (NADH-GDH and NAD-GDH, EC 18.104.22.168) were enhanced mainly in the leaves. It could be stated that tobacco leaves and roots exhibited similar salt sensitivity in terms of growth and NO3- assimilation (NR activity), however they showed differential response for salt ions accumulation and NH4+metabolism steps (GS and GDH).
Key words: Assimilation, growth, salt stress, nitrogen, mineral nutrition, tobacco.
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