Changes in Endogenous Cytokinin Levels in Kernels of Zea mays L. during Imbibition and Germination

In order to assess the potential role of endogenous cytokinins in the germination of Zea mays L. caryopses, cytokinin activity was determined in mature kernels and in kernels 1, 2, and 3 d after imbibition. Cytokinin activity was also recorded in the endosperm and embryo tissue of mature kernels and of kernels 3 d after imbibition to establish the localization and changes in the levels of endogenous cytokinins during imbibition and early germination. Using chromatographic, chemical, and enzymic techniques, compounds with chromatographic properties resembling those of zeatin, zeatin riboside, zeatin glucoside, zeatin riboside glucoside, and their respective dihydro derivatives were detected in extracts from mature maize kernels. From analyses of the endosperm and embryo tissue at the two stages, it appears that the cytokinin glucosides present in the endosperm are transported to the embryonic axis for utilization in growth and development of the seedling. This concept is supported by the fact that the levels of /?- glucosidase activity detected were highest in the embryos, particularly in the radicles, 3 d after imbibition.