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

Area of Science:

• Plant cell biology
• Molecular biology
• Cell cycle regulation

Background:

• Somatic plant cells possess a hormone checkpoint in late G2 phase.
• Cytokinin plays a role in regulating this checkpoint.
• p34cdc2 kinase activity is modulated during cell cycle progression.

Purpose of the Study:

• To investigate the role of cytokinin in regulating the G2 phase hormone checkpoint in plant cells.
• To elucidate the function of the mitotically active p34cdc2 kinase in plant mitosis.
• To determine the specific effects of the active plant metaphase kinase on microtubule structures.

Main Methods:

• Hormone treatment (cytokinin) to stimulate checkpoint response.
• Analysis of p34cdc2 kinase activity and its regulation by phosphotyrosine removal and Cdc25 phosphatase.
• Microinjection of active metaphase kinase into plant cells.
• Observation of microtubule dynamics (preprophase band, spindle, phragmoplast) using microscopy.

Main Results:

• Cytokinin stimulates phosphotyrosine removal from p34cdc2 kinase.
• Kinase activation increases as Cdc25 phosphatase activation capacity declines.
• Injected metaphase kinase specifically disassembles preprophase band microtubules.
• The kinase does not affect interphase microtubules, spindle, or phragmoplast.

Conclusions:

• The plant G2 phase hormone checkpoint involves cytokinin-mediated regulation of p34cdc2 kinase.
• The active plant metaphase kinase drives unique plant mitotic processes, including preprophase band disassembly.
• Plant metaphase kinase functions as MPF, promoting chromosome condensation and nuclear envelope breakdown.