Apical reactions to gibberellic acid application according to the genotype inSilene armeria

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Abstract
Two selected strains ofSilene armeria L. were used: S1-2 (GA-line, not induced to flowering by GA3 in SD of 8 h) and S2-1 (GA+ line which reacts to GA3 with flowering in non-inductive photoperiod). Moreover S1-2 and S2-1 differ in their critical daylength 14.5 and 8.0 h, respectively. Changes in the mitotic index and DNA content of cells in the various zones of the apical meristem during GA3 treatment were described. At the start of the experiment, the functioning of the apex was characterized by a predominance of G1 phase in the two strains. Therefore S2-1 differed by a higher mitotic activity specially in the central zone. In S1-2, GA3 acted mainly on the rib-meristem cells, which resulted in stem elongation. Lack of response in the cells of the central zone explains why GA3 fails to induce flowering in this strain. In S2-1, GA3 acted mainly on the central zone where a gradual increase in mitotic acitivity and in the percentages of nuclei at the (S + G2) level was recorded. This stimulation brought the meristems into the prefloral stage. The differences between the two strains are discussed according to the status of control meristems. The reactions induced by GA3 were compared with the pattern of changes during induction, in LD.