Nitrate Transport Characteristics inHordeum vulgareL. Seedlings using Three Different Tracer Techniques

Deane-Drummond, C. E. and Thayer, J.R. 1986. Nitrate transport characteristics in Hordeum vulgare L. seedlings using three different tracer techniques.—J. exp. Bot. 37: 429–439. $CIO363-$, $NO133-$ and $NO153-$ have been used to investigate various properties of nitrate uptake and translocation into Hordeum vulgare L seedlings. Short term $CIO363-$/$NO3-$ influx into seed lings grown in CaSO⁴ was stimulated by $NO3-$ after a lag of 2 h. The apparent kinetics of short term $NO133-$ influx over the concentration range 0·0–0·7 mol m fitted Michaelis-Menten equations The apparent V_max did not change when seedlings were used that had been pretreated in 10 or 100 mmol m⁻³$NO3-$ and V_max=3.77 and 3·56μmol g⁻¹ fr. wt. h⁻¹ respectively. The apparent Michaelis constants were also similar and K_m=0·47 and 0·45 mol m⁻³ respectively. Longer term pulse chase experiments with the heavy isotope ¹⁵N have shown that feeding roots with $NO153-$ resulted in the preferential appearance of ¹⁵N labelled amino acids in the xylem sap. Pulse chase experiments with the radioisotope ¹³N have shown that feeding shoots with $NO133-$ resulted in a radial pattern of distnbution of label in the leaf veins, which can be detected using autoradiography. The limitations and advantages of all three techniques are compared by reference to other known experimental data.