Control by cytokinins of the cellular behavior in the plate meristem of zucchini cotyledons

Abstract

The temporal and spatial effects of exogenous cytokinins on both cell expansion and division activity in the plate meristem of cultured zucchini cotyledons were studied. N6-benzylaminopurine (1-100 microM) and N-(2-chloro-4pyridyl)-N'-phenylurea (4PU-30) (0.1-100 microM) greatly stimulated the cell growth and division. They provoked multiple cell cycles, formation of larger clusters of daughter cells and an increase of the final number of cells. Both cytokinins led to earlier achievement of final cotyledon size and shortened the cell doubling time. By contrast to the purine cytokinin, phenylurea cytokinin 4PU-30 enlarged the cotyledon predominantly in length. Zeatin and kinetin were less effective, particularly in stimulating cell expansion. In low concentrations, all cytokinins were more effective in stimulating division activity rather than expansion. The cells in the cotyledon margins displayed a higher division activity, especially when treated with exogenous cytokinins. The final cotyledon and cluster areas were not of the strict proportional dependence upon the number of their cells. These results provide a novel example where stimulated cell division fails to evoke a respective increase in the final organ size.

Modulating zucchini cotyledon plate meristem activity by interactions between the cycline-dependent kinase inhibitor roscovitine and cytokinins

“…However, the effect of 400 lM roscovitine varied in the different seed batches: no effect; stimulatory or inhibitory. The exogenous BA substantially enhanced the cotyledon enlargement and respectively, the growth of cotyledon units (the growth in area of the daughter cells resulted from the initial palisade cells) as already shown by Stoynova-Bakalova and Petrov (2006). When the cotyledon was well supplied with cytokinins, the stimulation caused by 200 lM roscovitine on the cotyledon growth was greater (in a combined treatment with BA; Figs.…”

“…We have not found a concentration dependency on the exogenous cytokinin in the zucchini cotyledon marginal cells (Stoynova-Bakalova and Petrov 2006) and have expected analogous parameters of growth and cell division provoked by both roscovitine concentrations. The evaluated parameters are somewhat different, however, always testifying to a significant stimulation of both cluster area enlargement and cell division.…”

“…The main stimulators of the early postembryonic cotyledon growth and plate meristem activity are exogenous cytokinins, acting in a concentration-dependent manner (Stoynova-Bakalova et al 2002;Stoynova-Bakalova and Petrov 2006). The similar (however, somewhat lower) activation of both cell division and growth, found in roscovitine-treated cotyledons, testifies to elevated levels of active endogenous cytokinins.…”

“…Exogenous cytokinins usually lead to some lamina deformations, to formation of more or less uneven surfaces of cotyledon blades (Stoynova-Bakalova and Petrov 2006). It is known that cytokinin activates one of the cyclins, CysD3, whose over-expression results in undulated leaves (Riou-Khamlichi et al 1999).…”

“…Recently the use of plate meristem of Arabidopsis cotyledons (Stoynova-Bakalova et al 2004) and that of cultivated (isolated from dry seeds) Cucurbita cotyledons (StoynovaBakalova 2007;Stoynova-Bakalova et al 2002, 2008Stoynova-Bakalova and Petrov 2006) has been introduced as efficient experimental systems giving an opportunity for simultaneous and exact quantifying of cell growth and proliferation during the organ growth. The second innovative model system consists of monolayers of palisade cells, whose constant height is conserved by the anticlinal divisions and lateral cell growth.…”