Inhibition of Cell Proliferation and Expansion in Vitro by Three Stem Growth Retardants

Three inhibitors of stem elongation, Amo, CCC, and Phosfon, inhibit cell division and expansion in tissues cultured in vitro. However, contrary to the case in intact plants, gibberellic acid does not prevent the retardant‐induced inhibition in vitro. Supplementary auxin is also without effect in preventing the inhibition. Thus, the effect of the retardants cannot be simply that of inhibiting gibberellin or auxin synthesis. With respect to growth, carrot, chrysanthemum, and geranium tissues are equally sensitive to all 3 retardants, whereas tobacco tissues are considerably more resistant to Amo and apparently unaffected by CCC.