Etude structurale, fonctionnelle et métabolique du méristème apical jeune de l’Isoetes setacea

Abstract

The apical meristem of Isoetes setacea Lam. is morphologically and cytologically individualized after the third plastochron. Compared with the adult, the young meristem is characterized by reduced dimensions and the absence of structural and functional zonation. In these young meristems, cells have a very fast RNA turnover and a short cell cycle in which the presynthesis phase, G1, is preponderant. No cells exhibiting morphological, cytological, or metabolical characters typical of filicinean apical cells have been recognized.

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“…Perhaps the slow growth rate at the apical summit prevents primordia from being formed there, just as much as the rapid rate on the flanks allows it. However, in young apices of the pteridophytes Isoetes and Pohpodium, w^hich are making primordia, the rate of growth in the central, axial cells is the same as that of the peripheral cells where the primordia are initiated (Michaux-Ferriere, 1980. ln this case, a higher rate of growth at the primordial sites cannot be essential for primordium initiation.…”