Reduction of nitrate (¹³NO₃) influx and nitrogen (¹³N) translocation by tomato and melon varieties after short exposure to calcium and potassium chloride salts

Abstract

The effect of KC1 or CaCl₂ pretreatments on ¹³NO₃ influx into melon or tomato roots was investigated. Plants, previously grown in 1/10 strength Johnson's solution, were exposed for 10 min to 1/10 strength Johnson's solution supplemented with various concentrations of KCl or CaCl₂. These solutions were than replaced by identical solutions labeled with ¹³NO₃. After 10 minutes, plants were washed, roots were separated from the tops, introduced into counting vials and radioactivities counted for 30 seconds and corrected for decay. The influx of ¹³NO₃ to the roots of melon (Cucurbita pepo L.), cultivars Rochet and Eshcolit Amakim, and tomato (Lycopersicon esculentum L.), cultivars M‐82 and VF‐785 was depressed at moderate concentrations (10–60 mol/m³) of CaCl₂. By contrast, KC1 did not inhibit ¹³NO₃ influx. Tomato plants translocated about 30% of their total ¹³N label to the shoot at low salt concentration. This proportion was significantly reduced by increased concentrations of KCl or CaCl₂ in the external medium. In melons, the influx values were lower than those of tomato and only insignificant amounts of the ¹³N label (no more than 3.5%) were transferred to the shoot during the 10 min labeling time. Salt tolerant cultivars of both melon and tomato had higher nitrate influx rates than salt sensitive ones.