Magnitude and Kinetics of Stem Elongation Induced by Exogenous XXXX in Intact Light-Grown @entity3587 Seedlings.

@entity6207 @entity3587 @entity9634 @entity2708
Exogenously applied @entity9634 ( @entity6207 ) strongly promoted stem elongation over the long term in intact light-grown seedlings of both dwarf (cv Progress No. 9) and tall (cv Alaska) @entity3587 ( @entity3587 .), with the relative promotion being far greater in dwarf plants. In dwarf seedlings, solutions of @entity6207 (between 10-4 and 10-3 M), when continuously applied to the uppermost two internodes via a @entity2708 wick, increased whole-stem growth by at least 6-fold over the first 24 h. The magnitude of growth promotion correlated with the applied @entity6207 concentration from 10-6 to 10-3 M, particularly over the first 6 h of application. @entity6207 applied only to the apical bud or the uppermost internode of the seedling stimulated a biphasic growth response in the uppermost internode and the immediately lower internode, with the response in the latter being greatly delayed. This demonstrates that exogenous @entity6207 effectively promotes growth as it is transported through intact stems. @entity6207 withdrawal and reapplication at various times enabled the separation of the initial growth response (IGR) and prolonged growth response (PGR) induced by auxin. The IGR was inducible by at least 1 order of magnitude lower @entity6207 concentrations than the PGR, suggesting that the process underlying the IGR is more sensitive to auxin induction. In contrast to the magnitude of the @entity6207 effect in dwarf seedlings, applied @entity6207 only doubled the growth in tall seedlings. These results suggest that endogenous @entity6207 is more growth limiting in dwarf plants than in tall plants, and that auxin promotes stem elongation in the intact plant probably by the same mechanism of action as in isolated stem segments. However, since dwarf plants to which @entity6207 was applied failed to reach the growth rate of tall plants, auxin cannot be the only limiting factor for stem growth in @entity3587 .
