Radioimmunoassays for trans-zeatin and related cytokinins

Abstract

Radioimmunoassays for the quantitation of trans-zeatin and related cytokinins have been developed. Antisera produced against bovine serum albumin conjugates of trans-zeatinriboside have a high affinity (K_a=2.4.10^-11 M) for zeatinriboside and for zeatin, but show a negligible cross reaction to isopentenyladenosine (0.1%) and cis-zeatinriboside (0.4%), only a slight cross reaction to dihydrozeatin (1.7%), and no cross reaction at all to other purines, such as adenosine and related, compounds, was observed. The assays are sensitive and measuring ranges extend from 0.06–30 pmol (0.02–10 ng) of zeatinriboside. This has been achieved by employing as tracers immunoreactive zeatin derivatives with high-specific activity, (tritiated zeatinriboside-dialcohol: 8.37.10¹¹ Bq mmol^-1 and zeatinribosyl-[¹²⁵I]tyramine: ca. 1.9.10¹³ Bq mmol^-1. The detection limit is 40 fmol (15pg) for the assay employing the tritiated tracer, and assay reproducibility is high (variation coefficients of triplicates less than 5%). Several hundred assays can be completed in one day, and, due to the high specificity of this assay, crude extracts may be used for analysis. The course of zeatin levels in developing fruits of Lycopersicon esculentum cv. Moneymaker is given.