REGULATION OF GROWTH AND GRAVITROPISM IN THE PEANUT GYNOPHORE
This investigation set out to examine the role of plant growth regulators in cell growth and gravitropism of the peanut gynophore. Gibberellin and auxin were found to be important in regulating growth and gravitropism of gynophores in situ. Endogenous auxin levels appeared to be sub-optimal as low concentrations of applied IAA caused them to bend away from the point of application. Both auxin and ACC caused gynophores to alter their gravitropic orientation. Experiments looking at 14C-IAA transport within the gynophore indicated that any ethylene-induced bending was apparently not caused by altered auxin transport. Dose-response relationships were obtained for the growth regulators auxin and gibberellin using excised and depleted gynophore as well as internodal sections. Different optima were observed for the two tissue types. This suggested that either different sensitivities to IAA and GA3 existed within the two shoot systems or that quantitative differences in endogenous levels of IAA and GA3 were present. Further investigations indicated that ethylene altered the responsiveness of gynophore sections to auxin - this effect being specific to sub-optimal IAA concentrations. It was concluded that ethylene could possibly affect sensitivity to auxin of gynophores in situ. These results are discussed in relation to current views on hormonal regulation of gravitropism and general growth regulator action in plants.
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