Reduction of nitrate (13no3) influx and nitrogen (13n) translocation by tomato and melon varieties after short exposure to calcium and potassium chloride salts

The effect of KC1 or CaCl2 pretreatments on 13N03 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 KC1 or CaCl2. These solutions were than replaced by identical solutions labeled with 13N03. 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 13N03 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 13NCO3 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 KC1 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.