État nucléaire des méristèmes du pois dans la graine sèche; imbibition et reprise du cycle cellulaire

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Abstract
In the dry seed of pea (Pisum sativum cv. Nain Hâtif d'Annonay), the shoot and root meristematic cells are arrested at specific phases of the cell cycle, showing organ specificity. The root apex contains resting nuclei both at the 2C- and 4C-DNA levels in approximately the same proportions; the shoot apex possesses nuclei arrested only at the 2C-DNA level. The emergence of the radicle (20th–24th hour) follows a 100% increase in fresh weight (16th hour) and is due to cell elongation only. Under dark conditions, this emergence occurs at the same time than the beginning of the S period (24th hour) from the 2C nuclei of root meristematic cells. The first mitoses of 4C nuclei occur only at the 26th hour of imbibition. In the shoot apex, the cell cycle does not start with the 2C nuclei entering the S period before the 36th hour under dark conditions, and later, in light conditions. The first mitoses begin around the 48th hour, suggesting a S + G2 period of about 12 h. These data are discussed in relation to the mechanisms responsible for the various types of blockage or control of the cell cycle.

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