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 [Te-99m]TcO4-, [S-35] SO42- and H-2[P-32]PO4- 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 NO3-. In experiments lasting 24 h, net TcO4- uptake decreased at higher NO3- supplies. The inhibitory effect of NO3- on TcO4- uptake also was shown in TcO4- influx experiments (K-i = 3.3 mM), although about 30% of the TcO4- influx is suggested to be insensitive to NO3-. In contrast, H2PO4- (30 mM) did not inhibit TcO4- influx, whereas SO42- (30 mM) tended to increase TcO4- influx, probably due to the ionic strength of the uptake solution. Significant effects of the NO3- supply on Tc efflux were not found. Overall, this leads to the conclusion that TcO4- and NO3- share at least one transporter.