Absorption and translocation of gibberellic acid in the grapevine

Abstract

1. Studies were made on the absorption and translocation patterns of nonradioactive gibberellin and carbon-14-gibberellin.
2. When the mature leaves of young shoots of Zinfandel or the stem and the leaf axils were sprayed with nonradioactive compound at 10 ppm about equal stimulation of shoot growth resulted. Much response to gihberellin was obtained when the first leaf above the first mature leaf was treated. Treatment of the internode below the first mature leaf gave results similar to that of treating the first mature leaf. Another experiment showed that the young internodes gave more response than older ones to gibberellin.
3. Studies with radioactive gibberellin showed that intact internodes and leaves were very poor avenues for entry of gibberellin. Movement was mainly to the actively growing shoot tip. Considerable movement through the buds occurred, and after the internode was scratched, much gibberellin entered the plant and moved upwards in the xylem.
4. Most carbon-14-gibberellin was absorbed and translocated when the base of the upper surface of the leaf was treatEd and least when the tip was treated. Treatment of the center of the leaf gave intermediate results. Less gibberellin was exported from V. riparia leaves than from the Riesling. Leaves about four-fifths full size and still light ,green afforded some penetration and resultant translocation, but little or no penetration occurred in the older leaves. In one experiment no visible movement of gibberellic acid out of the leaf occurred during the first day, and most movement was demonstrated after seven days.