Mitotic Activities and Levels of Nuclear DNA in the Apical Meristem of Silene armeria (strain S1.2) Following Application of Gibberellin A_3

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Strain S1.2 of Silene armeria was grown under an 8h-photoperiod and treated with GA_3 every day for 20 days. This growth substance caused stem elongation, but no flowering in this long-day plant. Changes in the mitotic index and DNA content of cells in the various zones of the apical meristem before, during and after GA_3 treatment were de-scribed. Mitotic activity and increase in the proportion of nuclei at the 4C level (S+G_2 phase of the cell cycle) were strongly stimulated in the rib-meristem, and to a lesser extent in the lateral zone, but not in the axial zone. This stimulation of apical activity reached a peak after two GA_3 treatments and then declined gradually, so that after 20 days the activity in GA_3-treated meristems was lower than that in untreated controls; at this point most cells were in the G_1 phase. When the GA_3 treatment was discontinued, there was a gradual increase in the mitotic activity which ultimately reached the same level as that in controls. Stem elongation ceased and leaves formed aerial rosettes. It is concluded that in vegetative plants of strain S1.2 of Silene armeria GA_3 acts mainly on the rib-meristem cells which- results in stem elongation. Lack of response in the axial cells explains why GA_3 fails to induce flowering in this strain of Silene armeria.
日本植物生理学会の論文