Changes in growth and activity of enzymes involved in nitrate reduction and ammonium assimilation in tomato seedlings in response to NaCl stress.
OBJECTIVE
In Tunisia, salt water is largely used for tomato irrigation. In this work, a study was made of the changes in the nitrate reduction and ammonium assimilation into amino acids in tomato seedlings under salinity in order to providee further insight into the salt effects on plant growth. Methods Ten-day-old tomatoes (Solanum lycopersicum) were subjected to 100 mm NaCl stress, and nitrogen metabolism in leaves and roots was studied.


RESULTS
The concentrations of Na+ and Cl- rapidly increased in the leaves and in the roots following exposure of tomato seedlings to NaCl stress. In contrast, the NO3- concentrations were lowered first in the roots and later in the leaves. From 5 to 10 d of treatment, salt ions provoked a decrease in the dry weight and an increase in the NH4+ concentrations in the leaves. Inhibition was observed in the leaves for the activities of nitrate reductase (NR, EC 1.6.6.1), ferredoxin-dependent glutamate synthase (Fd-GOGAT, EC 1.4.7.1) and deaminating glutamate dehydrogenase (NAD-GDH, EC 1.4.1.2). NaCl affected these enzyme activities less in the roots than in leaves. This was in accordance with the pronounced decrease of dry weight by salt in leaves compared with that in the roots.


CONCLUSIONS
NaCl stress effects on growth, metabolite concentrations and enzyme activities depended on the duration of salt treatment and the plant tissue.
Debouba
Mohamed
M
Unité de Recherche Nutrition et Métabolisme Azotés et Protéines de Stress 99/UR/C 09-20, Département des Sciences Biologiques, Faculté des Sciences de Tunis, 1060 Tunisie.
Maâroufi-Dghimi
Houda
H
Suzuki
Akira
A
Ghorbel
Mohamed Habib
MH
Gouia
Houda
H
D000594:Amino Acid Oxidoreductases / Q000378:metabolism; D018551:Solanum lycopersicum / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D050901:Nitrate Reductase / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology*; D013997:Time Factors
D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D012965:Sodium Chloride; D000594:Amino Acid Oxidoreductases; C042233:glutamate synthase (ferredoxin); D050901:Nitrate Reductase