The histone deacetylase (HDA) inhibitors, trichostatin A (TSA) and HC toxin halt mitosis in cultured root meristems of Pisnum sativum, while the anti-protozoan HDA inhibitor apicidin is ineffective. Two-dimensional PAGE of proteins from root meristems exposed to TSA and HC toxin did not show significant differences compared to controls, although a previously tested HDA inhibitor, butyrate, exhibited dramatic variations in its protein profile. Northern analysis of butyrate- and TSA-treated root meristems indicated that non-proliferating cells are expressing significant amounts of transcripts of the known cell proliferation associated genes: histone H2A, MAP kinase, cycA2:1 and cdc2. Western analysis reveals the presence of hyperacetylated nuclear proteins in HDA-inhibitor treated cells. These results suggest that the HDA inhibitors, butyrate and TSA, halt mitosis without down-regulating genes that typically have low or nonexistent expression levels in non-dividing cells.