Effect of BAP and IAA on the expression of G1 and G2 control points and G1-S and G2-M transitions in root meristem cells of Vicia faba.

Excised, carbohydrate-starved root meristems of Vicia faba subsp. minor have been used to investigate the impact of the auxin indole-3-acetic acid (IAA) and the cytokinin benzyl-6-aminopurine (BAP) on (1) the expression of Principal Control Points (PCPs) during the G1- and G2-phases of the cell cycle, and (2) the dynamics of sucrose-mediated resumption of DNA replication and mitosis (G1-to-S and G2-to-M transitions). Compared with the excised root tips starved in mineral medium without hormones, stationary phase meristems induced during continuous treatment with BAP, IAA, or a mixture of BAP+IAA, increased the number of G2 cells, producing characteristic profiles of nuclear DNA content. In medium containing 2% sucrose, BAP accelerated PCP1-->S and PCP2-->M, whereas continuous treatment with IAA resulted in marked prolongation of both transitions. Since the PCPs regulate progression through the key events of interphase and mitosis by interacting with cyclin dependent kinases (CDKs), these results seem to correspond with current data indicating functional connections between phytohormones, nutritional signals, gene expression and the cell division cycles in plants.