Cytokinins and Their Possible Role in Seed Size and Seed Mass Determination in Maize

One of the richest sources of CKs in various plants species are developing seeds. In fact, zeatin, a major natural CK, was first discovered in developing seeds of maize (Letham, 1963). Not surprisingly, developing seeds of maize, rice and Lupinus albus have played a major role in CK research (reviewed in Emery & Atkins, 2005). A major focus of these studies has been on the possible role of CKs in sink strength of developing seeds. The role of CKs in controlling sink strength is inferred largely from (a) the well known role of CK in stimulating cell division that may lead to increased organ size of the sink tissue, and (b) the coincidence of CK accumulation with seed cell division profiles in several plant species (Dietrich et al., 1995; Arnau et al., 1999; Yang et al., 2002).