Concentration Gradients of trans-Zeatin Riboside and trans-Zeatin in the Maize Stem

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Abstract
A sensitive, specific enzyme immunoassay (EIA) for trans-zeatin riboside (ZR) and trans-zeatin (Z) in the 0.3-30 pmol range was described. The reliability of the method for measuring ZR + Z in partially purified extracts of Z. mays L. tissues was verified by high-performance liquid chromatography. EIA measurements showed that there was a concentration gradient of ZR + Z along the length of the Zea stem. The topmost internodes, internodes 7 and 8 counting from the coleoptilar node, had the highest concentration (.simeq. 130 pmol/g fresh weight). Moving basipetally, the concentration dropped .simeq. 10-fold to a minimum at internode 4, and then increased slightly in internodes 2 and 3. There were also gradients within each internode. The 5 lowest internodes contained the highest concentrations toward their apical end, the region which included the node; this asymmetry was less pronounced near the top of the plant.