CALCIUM-DEPENDENT ASYMMETRIC MOVEMENT OF H-3 INDOLE-3-ACETIC-ACID ACROSS GRAVISTIMULATED ISOLATED ROOT CAPS OF MAIZE

There is evidence that the cap is the initial site of lateral auxin re distribution during the gravitropic response of roots. We tested this further by comparing asymmetric auxin redistribution across the tips o f gravistimulated intact roots, decapped roots, isolated root caps and isolated apical sections taken from decapped roots. Gravistimulation caused asymmetric (downward) auxin movement across the tips of intact roots and isolated root caps but not across the tips of decapped roots or across isolated apical root segments. Naphthylphthalamic acid and pyrenoylbenzoic acid, inhibitors of polar auxin transport, inhibited a symmetric auxin redistribution across gravistimulated isolated root ca ps and across the tips of gravistimulated intact roots. For intact roo ts there was a positive correlation between the extent of inhibition o f asymmetric auxin redistribution by polar auxin transport inhibitors and the extent of inhibition of curvature. The calcium chelating agent , ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic aci d, also caused parallel inhibition of asymmetric auxin redistribution and gravitropic curvature and this effect was reversed by subsequent t reatment with calcium. The results support the hypothesis that the cap is a site of early development of auxin asymmetry in gravistimulated roots and that calcium plays an important role in the development of l ateral auxin redistribution.