Effect of Nitrate on Uptake of Pertechnetate by Tomato Plants

Nitrate has been shown to affect the acquisition of the nuclear waste product technetium (Tc) by plants. The mechanism responsible for this phenomenon is unknown. The uptake of [99mTc]TcO−4, [35S] SO2−4 and H2[32P]PO−4 was studied in tomato plants (Lycopersicon esculentum Mill., cv. Tiny Tim) with different growth rates due to culture at 0.5, 4.0, or 30 mM NO−3. In experiments lasting 24 h, net TcO−4 uptake decreased at higher NO−3 supplies. The inhibitory effect of NO−3 on TcO−4 uptake also was shown in TcO−4 influx experiments (Ki = 3.3 mM), although about 30% of the TcO−4 influx is suggested to be insensitive to NO−3. In contrast, H2PO−4 (30 mM) did not inhibit TcO−4 influx, whereas SO2−4 (30 mM) tended to increase TcO−4 influx, probably due to the ionic strength of the uptake solution. Significant effects of the NO−3 supply on Tc efflux were not found. Overall, this leads to the conclusion that TcO−4 and NO−3 share at least one transporter.