EFFECTS OF PH AND NITRITE ON POTASSIUM UPTAKE AND GROWTH OF RICE SEEDLINGS

The effects of increasing concentrations of NaNO2 on the K+ uptake of rice seedlings (Oryza sativa L. cv. Oryzella) were studied at differen t pH values. Increasing concentrations of NaNO2 caused decreases in th e K+ uptake of the roots. When NaNO3 was present in the uptake solutio n, marked changes were not observed in the K+ uptake. The inhibitory e ffect of NO2- was strongly influenced by the H+ concentration of the o uter medium. A decrease of the pH of the external solution led to an i ncreased inhibitory effect of NO2- on both the ion uptake and the grow th of the seedlings. However, the reverse was true in the case of Nauptake. The inhibitory effect of NO2- was different for roots and shoo ts. Marked changes in the K+ efflux properties were not observed at pH 6. A decrease of the pH of the efflux medium, however, led to an incr eased loss of K+ from the roots. The results strongly suggest a distin ct role of NO2- in membrane damage at lower pH.