Cytokinins as Phytohormones — Sites of Biosynthesis, Translocation, and Function of Translocated Cytokinin

Abstract

This chapter assesses sites of cytokinin biosynthesis, cytokinin translocation, and the function of this translocated cytokinin. Cytokinins have been found in roots, stems, leaves, flowers, fruits, and seeds, and are probably present in all living cells of intact higher plants. However, establishing unequivocally which particular organs or tissues are sites of cytokinin biosynthesis has proved to be a perplexing problem. Marked cytokinin production follows adventitious root formation. Root development on petioles of excised bean leaves results in marked increases in the cytokinin level in the laminae. Determination of the cytokinin level, by reliable methods, along primary roots is important in relation to the site of cytokinin biosynthesis and the role of cytokinin in control of the site of lateral root initiation. Cytokinin levels increase in buds of excised poplar shoots that lack roots about the time of bud burst. A number of reports substantiate the view that cotyledons are supplied with cytokinin from the axis.