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 io n uptake of wheat (Triticum aestivum L. cv. GK Othalom) seedlings were studied at different pH values. Without pretreatment, the higher the concentration of NaNO2 the greater was the decrease in uptake of K+ in to the roots, both at pH 4 and pH 6. At pH 6 but not at pH 4 the rever se 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 nitr ate. Nitrite at 0.1 mM in the medium induced the development of an upt ake system for both NO2- and NO3- in wheat roots. At higher concentrat ions pretreatment with NO2- decreased NO3- uptake by the roots, but NO 3- did not inhibit the uptake of NO2-. The toxic effect of NO2- was st rongly pH dependent. Lower pH of the external solution led to an incre ased inhibition by NO2- of both ion uptake and growth of seedlings. Th e inhibitory effect of NO2- differed considerably for roots and shoots . The roots and especially the root hairs were particularly sensitive to NO2- treatment.