Effect of nitrate on uptake of pertechnetate by tomato plants

Nitrate has been shown to affect the acquisition of the nuclear waste produ ct 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- wa s studied in tomato plants (Lycopersicon esculentum Mill., cv. Tiny Tim) wi th different growth rates due to culture at 0.5, 4.0, or 30 mM NO3-. In exp eriments lasting 24 h, net TcO4- uptake decreased at higher NO3- supplies. The inhibitory effect of NO3- on TcO4- uptake also was shown in TcO4- influ x experiments (K-i = 3.3 mM), although about 30% of the TcO4- influx is sug gested to be insensitive to NO3-. In contrast, H2PO4- (30 mM) did not inhib it TcO4- influx, whereas SO42- (30 mM) tended to increase TcO4- influx, pro bably 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.