Inhibition of Shoot Geotropism by Neutral Buffers

Abstract

Submerged hypocotyl sections from Helianthus annuus cv. Sungold were used to test the effect of neutral buffers on shoot geotropism. When hypocotyls are abraded, increasing the molarity (0.25-20 mM) of pH 6.8 K-phosphate buffer, as well as other buffering systems, results in a strong inhibition of geotropic curvature. Buffer strength has no such effect on the curvature of nonabraded segments. Asymmetric shoot growth following geostimulation may require the establishment of a proton gradient across the cell walls of the shoot. When neutral buffers have access to the wall space (i.e., in abraded segents), they may prevent the establishment of such a gradient.