Catecholamine stimulation of the gibberellin action that induces lettuce hypocotyl elongation

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Abstract
Effects of catecholamines and their derivatives on gibberellic acid (GA)-induced lettuce hypocotyl elongation was studied, because catecholamines have a chemical structure similar to the dihydroconiferyl alcohol that has been isolated from lettuce cotyledons as a GA synergist. Epinephrine, norepinephrine, dopamine and 3,4-dihydroxymandelic acid synergistically enhanced the promoting effect of GA on hypocotyl elongation. In contrast, metanephrine, normetanephrine, DOPA and 3-methoxy-4- hydroxymandelic acid did not enhance the GA effect. The action of catecholamines was inhibited by trans-cinnamic acid which competitively inhibited the action of dihydroconiferyl alcohol; this suggests that the receptor site for catecholamines is the same as that for dihydroconiferyl alcohol. The basic ethyl acetate fraction from lettuce seedlings synergistically enhanced the GA effect. TLC analyses of this basic ethyl acetate fraction revealed that the chromatographic area corresponding to authentic catecholamines could enhance the GA effect. From these results, a possible role for catecholamines in the regulation of lettuce hypocotyl elongation caused by GA was posited, and is discussed here.

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