Expression of CKS1At in Arabidopsis thaliana indicates a role for the protein in both the mitotic and the endoreduplication cycle

Although endoreduplication is common in plants, little is known about the m echanisms regulating this process. Here, we report the patterns of endoredu plication at the cellular level in the shoot apex of Arabidopsis thaliana L . Heynh. plants grown under short-day conditions. We show that polyploidy i s developmentally established in the pith, maturing leaves, and stipules. T o investigate the role of the cell cycle genes CDC2aAt, CDC2bAt, CYCB1;1, a nd CKS1At in the process of endoreduplication, in-situ hybridizations were performed on the vegetative shoot apices. Expression of CDC2aAt, CDC2bAt, a nd CYCB1;1 was restricted to mitotically dividing cells. In contrast, CKS1A t expression was present in both mitotic and endoreduplicating tissues. Our data indicate that CDC2aAt, CDC2bAt, and CYCB1;1 only operate during mitot ic divisions, whereas CKS1At may play a role in both the mitotic and endore duplication cycle.