Nitrate reductase activity and yield of dry mass and protein content in cucumber cucumis sativus cultivar monastyrski seedlings supplied with nitrates and ammonium

Buczek, J.; Burzynski, M.

Acta Societatis Botanicorum Poloniae 48(3): 465-472


ISSN/ISBN: 0001-6977
Accession: 005984798

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The presence of NH4+ ions in a nutrient solution containing NH4NO3 with the K+ ions removed caused an inhibition of nitrate reductase (NR) activity in cucumber leaves. The lack of K+ in a NaNO3 medium also decreased the NR activity. Addition of K+ to these media suppressed the inhibitory effect of NH4+ and enhanced the NR activity in the leaves of plants growing in NaNO3 nutrient solution. Apparently K+ is essential for NO3- reduction, Na+ is less effective in this process and NH4+ ions markedly inhibit NO3- reduction. The protein content and increment of dry mass of cucumber plants grown 10 days with NH4-N as the sole N source was significantly lower as compared with NO3-N supplied plants or with plants fed with both forms of mineral N (NH4NO3). The results show that cucumber prefers the nitrates, although it can utilize the ammonium form of N.