Gravity-induced asymmetric distribution of a plant growth hormone.

H.E. Dolk demonstrated that gravistimulation induced an asymmetric distribution of auxin in a horizontally-placed shoot. We wish to determine where, and how that asymmetry arises and have demonstrated that the endogenous auxin, indole-3-acetic acid, becomes asymmetrically distributed in the cortical cells of the Zea mays mesocotyl during 3 min of geo-stimulation. Further, indole-3-acetic acid derived by hydrolysis of an applied transport form of the hormone, indole-3-acetyl-myo-inositol, becomes asymmetrically distributed within 15 min of geo-stimulus time. From these and prior data we have developed a working theory that the gravitational stimulus induces a selective leakage, or secretion, of the hormone from the vascular tissue to the cortical cells of the mesocotyl.