In vivo measurement of cadmium ((115m)Cd) transport and accumulation in the stems of intact tomato plants (Lycopersicon esculentum, Mill.) : II. Lateral migration from the xylem and redistribution in the stem.

The internal distribution processes of cadmium ((115m)Cd) in the stems of tomato plants have been investigated using in vivo β-spectrometric measurements with semiconductor detectors. The initial penetration into the xylem after root uptake and the subsequent lateral redistribution in the surrounding tissues were monitored continuously in each individual plant. The kinetics of the lateral migration toward the epidermis can be described by a diffusion process, characterized by an apparent diffusion coefficient of about 10(-8) cm(2) s(-1). After two days of cadmium supply this heavy metal is accumulated in relatively large amounts in the epidermal and cortical layers, from which it can be released only very slowly. On the contrary, the exchange processes with other divalent cations cause in the xylem a quick release, its rate being dependent on the duration of the preceding cadmium treatment.