Uptake and distribution of ¹⁴C-labeled Fosthiazate in tomato (Lycopersicon esculentum L.)

The uptake of ¹⁴C-labeled fosthiazate (0.75 mg.L^–1) by tomato plants was studied in solution culture both in the presence or absence of 2, 4 dinitrophenol (DNP, 1 × 10^–2 mM), a metabolic inhibitor. Fosthiazate was rapidly taken up by tomato plants and nearly one third of the finally absorbed quantity was taken up in the first half an hour. The translocation of fosthiazate to the shoot part was under metabolic control during the initial stage of uptake. The kinetics of uptake both in the presence and absence of DNP conformed well to the dual phase than a single phase. In the presence of DNP, the uptake capacity (V_max1) for the initial phase suffered, approximately three fold reduction in comparison to the absence of DNP while V_max2 for the latter phase was statistically similar to the value observed in the absence of DNP signifying the metabolic dependence of the initial uptake phase. Autoradiography indicated that fosthiazate in the tomato plants tends to accumulate in the roots and at the root-shoot junction. In shoot, it is accumulated in the older leaves especially, near the leaf tip and margins.