Nitrite in the root zone and its effects on ion uptake and growth of wheat seedlings

The immediate and posteffects of various concentrations of NaNO₂ on ion uptake of wheat ( Triticum aestivum L. cv. GK Öthalom) seedlings were studied at different pH values. Without pretreatment, the higher the concentration of NaNO₂ the greater was the decrease in uptake of K⁺ into the roots, both at pH 4 and pH 6. At pH 6 but not at pH 4 the reverse was true when the seedlings were pretreated with NaNO₂. Due to the high Na⁺ content of the roots, an effect of Na⁺ in this process cannot be excluded. Nitrite was taken up by the roots more rapidly than nitrate. Nitrite at 0.1 m M in the medium induced the development of an uptake system for both NO⁻₂ and NO⁻₃ in wheat roots. At higher concentrations pretreatment with NO⁻₂ decreased NO⁻₃ uptake by the roots, but NO₃ did not inhibit the uptake of NO₂. The toxic effect of NO⁻₂ was strongly pH dependent. Lower pH of the external solution led to an increased inhibition by NO⁻₂ of both ion uptake and growth of seedlings. The inhibitory effect of NO⁻₂ differed considerably for roots and shoots. The roots and especially the root hairs were particularly sensitive to NO⁻₂ treatment.