The plant cell cycle: conserved and unique features in mitotic control.

Somatic plant cells can use a hormone checkpoint in late G2 phase. Here cytokinin stimulates removal of phosphotyrosine from p34cdc2 kinase and concurrently capacity for activation of the kinase by Cdc25 phosphatase declines while activity of the kinase increases and cells enter mitosis. Processes unique to plant mitosis are driven by the mitotically active kinase since the enzyme taken from plant cells in metaphase, when injected, can disassemble the preprophase band microtubules that form in G2 phase at the site of the future cross wall. This action is specific, since microtubules are not depolymerised when in interphase cytoplasmic array, or spindle, or phragmoplast. Plant metaphase kinase acts as MPF by accelerating chromosome condensation and nuclear envelope breakdown.