Abstract
In carbohydrate-starved root meristems of <em>Vicia faba </em>subsp. minor, the expression of two Principal Control Points located at the final stages of the G1 (PCP1) and G2 (PCP2) phases has been found to be correlated with a marked decrease of protein phosphorylation within cell nuclei, nucleoli and cytoplasm. Adopting the same experimental model in our present studies, monoclonal FITC conjugated antibodies that recognize phosphorylated form of threonine (αT<sup>P</sup>ab-FITC) were used to obtain an insight about how the indole-3-acetic acid (IAA), benzyl-6-aminopurine (BAP), and the mixture of both phytohormones influence the time-course changes in an overall protein phosphorylation during sucrose-mediated PCP1→S and PCP2→M transitions. Unsuspectedly, neither IAA, BAP, nor the mixture of both phytohormones supplied in combination with sucrose did up-regulate protein phosphorylation. However using the block-and-release method, it was shown that root meristems of Vicia provided with sucrose alone indicated higher levels of αT<sup>P</sup>ab-FITC. Contrarily, phytohormones supplied in combination with sucrose induced apparent decline in phosphorylation of cell proteins, which - when compared with the influence of sucrose alone - became increasingly evident in time. Thus, it seems probable, that a general decline in the amount of αT<sup>P</sup>ab-FITC labeled epitopes may overlay specific phosphorylations and dephosphorylations governed by the main cell cycle kinases and phosphatases.
Highlights
A conserved network of surveillance pathways, called checkpoints, has evolved to delay or to block cell cycle progression in response to signals generated by various intracellular perturbations
Cytological data show that both positions, noted as carbohydrate-dependent, are relative and they refer to the respective shifts from G1 to S and from G2 to M (Vant Hof 1985)
Polit 1999; Polit et al 2003), root meristems starved for 72 h in carbohydrate-free medium were found to comprise two distinct populations of cells blocked in G1 and G2 phases, resolving phenotypic characters influenced either by PCP1 or PCP2
Summary
A conserved network of surveillance pathways, called checkpoints, has evolved to delay or to block cell cycle progression in response to signals generated by various intracellular perturbations. The effects described above prompted us to adopt the same model system for experiments aimed at determining the influence of BAP and IAA on the time-course changes in protein phosphorylation during sucrose-mediated PCP1®S and PCP2®M transitions in carbohydratestarved root meristem cells of Vicia faba.
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