Root elongation of Alaska pea seedling was suppressed by higher concentrations of growth retardants, CCC and ancymidol, than those required for shoot elongation. Gibberellic acid (GA3) led to recovery of ancymidol-inhibited elongation, with the concentration (1 nM) required for roots being lower than that for shoots (10μM). Ancymidol caused swelling of cortical cells in the elongating zone of the root, while GA3completely canceled this. These results suggest that roots require much less gibberellin than shoots for normal elongation growth.Growth kinetics recorded by a computer-regulated rhizometer indicated that the lag periods for growth suppression by ancymidol and growth recovery by GA3were about 10 h and 7 h, respectively.The composition of the cell wall sugars changed remarkably along the root axis from the tip to the base. The arabinose content was highest in the tip and rapidly decreased toward the base, whereas galactose complementarily increased toward the base. The thickened zone of ancymidol-treated roots had a higher galactose content than GA3-treated slender roots. Other neutral sugars were not significantly influenced by ancymidol and/or GA3. These results suggest that ancymidol makes cells short and thick with galactose-rich cell walls while GA3 keeps cells extensible and slender with galactose-poor cell walls
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