Nitrate reductase activity in tomato and cucumber leaves as influenced by NaCl and n source

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Abstract
The combined effects of NaCl and N nutrition (NO3 ‐ and NH4 ++NO3 ‐) on nitrate reductase activity (NRA) in intact tomato (Lvcopersicum esculentum) and cucumber (Cucumis sativus) seedlings were studied. NRA decreased in leaves of both plant species as salinity increased. Within each salinity level, NRA increased with the external NO3 ‐ concentration. An interference of C1‐ on NO3 ‐ uptake was observed. Based on these results, it appears that the NRA was affected directly by the presence of excessive NaCl in the root media at least in two ways, by either interfering with the uptake of NO3 ‐ by roots, or by inhibiting the transport of NO3 ‐ from vacuole to cytosol. The effects were accentuated by the presence of NH4 + as N source.