Inhibition of ion uptake and growth of wheat and rice exposed to nitrite at low pH

The effects of $NO_2^-$ on the ion uptake and growth of wheat (Triticum aestivum L. cv. GK Öthalom) and rice (Oryza sativa L. cv. Oryzella) seedlings were studied in hydroponic cultures at different pH values. Increasing concentrations of NaNO2 decreased the K+, $H_2PO_4^-$, $SO_4^{2-} and $NO_2^-$ uptake of the roots. The inhibitory effect of 1 mM $NO_2^-$ on ion uptake and growth was small or negligible between pH 6-7, but increasingly severe at lower pH. The inhibitory effect of $NO_2^-$ differed considerably for nutrients and was also different for species. Rice seedlings were more sensitive than wheat seedlings to $NO_2^-$ treatment. The parallel efflux studies revealed no significant effect of even high concentration of NaNO2 (10mM) of the K+ efflux of the roots at pH 6.5, but strongly enhanced the K+ efflux of the roots at pH 4 already at 1 mM NaNO2. The results indicate that $NO_2^-$ may initiate membrane damage at low pH. The presence of $NO_3^-$ in the uptake and/or growth solution decreased the inhibitory effect of $NO_2^-$.