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An autopolyploid that contains more than two sets of the same chromosomes causes apparent alterations in morphology, development, physiology and gene expression compared to diploid. However, the mechanisms for these changes remain largely unknown. In the present study, cytological observations of mature embryos and growing cotyledons demonstrated that enlarged organ size of an autotetraploid Arabidopsis was caused by cell size and not by cell number. Quantitative real time PCR (qRT-PCR) analysis of 34 core cell cycle genes revealed a subtle but stable increase in the expression of ICK1, ICK2 and ICK5 in autotetraploid seedlings. Autotetraploid Arabidopsis plants were found to be more sensitive to glucose treatment than diploid with decreased number of rosette leaves and suppressed root elongation. Cytological observations demonstrated that both cell proliferation and cell expansion of autotetraploid were dramatically suppressed under glucose treatment. Expression levels of ICK1, ICK5 together with Cyclin D and Cyclin B was increased under glucose treatment in both diploid and autotetraploid plants. These results suggest that ICK1 and ICK5 may be involved in developmental delay and that the suppressed growth under glucose treatment probably resulted from disturbed mitotic and endoreduplication cycle in autotetraploid Arabidopsis.