Changes in Cytokinin Activity during Seed Germination in Rice (Oryza sativa L.)

Cytokinin activity was determined in dry mature rice seeds, in endosperm and embryo tissues 24, 48 and 72 over imbibition and in radicles 96 h after germination. Cytokinins with chromatographic properties similar to zeatin, zeatin riboside, zeatin glucoside and zeatin riboside glucoside were datected in embryo and endosperm, but only the latter two were detected in mature seeds. Cytokinin activity was low during early toges of germination. Qualitative and quantitative changes in cytokinins were observed in both embryo and endosperm. The presence of higher cytokinin activity in the endosperm than in the embryo during the first 24 h after germination suggests that the endosperm may supply cytokinins until the embryo is able to synthaize its own cytokinins. The possible significance of high cytokinin glucoside activity in the embryo early during germination and high cytokinin activity in the radicle during the later stages is discussed.