Auxin and hydrogen ion actions on light-grown pea epicotyl segments I. Tissue specificity of auxin and hydrogen ion actions

Growth responses to added auxin and hydrogen ions of differentlyprepared tissue segments excised from 5th internodes of light-grownAlaska peas were studied. Unpeeled segments extended in responseto auxin but not to hydrogen ions. Peeled segments elongatedwell in response to hydrogen ions but much less when exposedto auxin. Hollow-cylinder (central part removed) and infiltrated(by reduced pressure) unpeeled segments significantly elongatedin response to hydrogen ions as well as to auxin. Outward curvatureof split segments was enhanced by buffer solution at pH lowerthan 5.0. Peeled segments secreted hydrogen ions into an incubationmedium containing auxin or a fungal toxin, FC. Unpeeled segmentsand the isolated epimermis secreted much less hydrogen ionsin response to these agents. Hydrogen ions generated by theaction of auxin thus seem to accumulate in the region adjacentto the cuticle, that is, epidermal cells. The significance ofthe epidermis in auxin and hydrogen ion actions is discussed. (Received May 17, 1974; )