The Stability and Movement of Gibberellic Acid in Pea Seedlings

Abstract

The stability and movement of gibberellic acid (GA) in intact dwarf pea seedlings growing in the light was studied by means of both unlabelled GA and GA labelled with isotopic carbon (14C). After 14C-GA had been applied to the mature leaves of pea seedlings much remained in association with the treated leaflets, but 14C-GA was also extractable from the young shoots. The yield was approximately the same 5 to 96 hours after treatment. GA penetrated leaf surfaces only while the application solvent was moist (about 1 hour), but moved from the treated leaflets into the shoots for at least 24 hours. Some hours after treatment there was an abrupt increase in the growth-rates of the plants, and crude estimates suggest that an effective dose of GA moved to the elongating tissue at about 5 cm/hr. The pattern of distribution of 14C was examined by autoradiography. The data suggest that GA which enters the plant is redistributed from maturing leaves to immature leaves, passing through the elongating tissue, for as long as any of the substance is present. The hypothesis remains tenable that GA produces its growth effects by acting only upon expanding tissue