Uptake and translocation of benzyladenine by elm shoots cultured in vitro

Abstract

The rate of uptake of 8-[14C]benzyladenine by Ulmus campestris L. (elm) shoots cultured in vitro was extremely rapid during the first 30-60 min of incubation. Total radioactivity, both in methanol extracts and in the pellet, continued to increase up to the 15th day in culture when shoots were transferred to a basal medium. After transfer, the 14C extracted and that remaining in the pellet diminished significantly, especially in the former, while only a small amount of radioactivity was released into the medium, suggesting that some 14C must have been released as 14CO2. A possible pathway leading to CO2 formation is described. Activated charcoal in the basal medium did not affect the loss of activity from the tissue. Benzyladenine was translocated into the upper half of the shoots quite rapidly (within 30 min) and benzyladenine degradation into a metabolite which cochromatographed with adenine was already detectable after 2 h in the lower half and 6 h in the upper half of the shoots. Throughout the 24-h feeding period, uptake was more rapid than degradation. By day 5, however, benzyladenine levels in the tissue were decreasing rapidly, reaching almost zero by day 15. In parallel, there was a transient increase in what is assumed to be adenine levels; the levels of products which cochromatographed with adenosine and adenine nucleotide were measured only during the 24-h feeding period and remained low throughout.