May activate cell cycle in the root apical meristem (RAM) and promote embryonic root (radicle) protrusion. Interacts with CDKA-1, CDKB2-1, KRP4/ICK7, KRP5/ICK3, KRP6/ICK4 and KRP7/ICK5. A number of isoforms are produced. According to EST sequences. Expressed in shoot apical meristem, leaf primordia vascular tissues and tapetum of anthers. Expressed throughout the cell cycle. Transiently expressed in the root tip during seed germination up to about 21 hours after stratification. Expressed during lateral root primordia formation, vascular tissue development, in fertilized ovules, and torpedo- and heart-stage embryos. By sucrose. Belongs to the cyclin family. Cyclin D subfamily.