May negatively regulate endocycles and act as a regulator of ploidy levels in endoreduplication. Expressed in tissues with active cell division: apical root and shoot meristems, lateral root and leaf primordia, floral meristems and developing pollen. Starts to be expressed during S phase with a maximum just before the G2-to-M boundary and disappears in the metaphase of mitosis. Expressed during embryogenesis in the ovule, integuments, egg cell and synergids, and in the embryo up to late-torpedo stage. Expressed during germination in the root apical meristem, shoot apical meristem, vascular bundles of the cotyledons and vascular cylinder of the roots up to lateral roots emergence. Expressed during flowering in the caulines leaves, peduncle, sepals of flower buds, early expanded petals, ovary, placenta, funiculi, devoloping ovules, pollen connective tissues, tapetum, endothecium, epidermis and developing pollen grains. By auxin in the roots, cytokinin in the shoot apex and sucrose in suspension cell culture. Down-regulated by salt stress in root meristem and shoot apex. Belongs to the cyclin family. Cyclin AB subfamily.