Autoregulation of Auxin Transport in Corn Coleoptile Segments

Abstract

Polar transport of auxin decreased and its net uptake increased in maize (corn) coleoptile segments preincubated in buffer following excision from the intact seedling. Reduced rate of cellular efflux of auxin accounted for these changes in preincubated segments where the endogenous auxin level was depleted. The difference in net uptake of auxin between freshly excised and preincubated tissues was completely abolished by the phytotropin N-1-naphthylphthalamic acid. Studies on in vitro binding of NPA to membrane vesicles isolated from the tissue indicated that the number of binding sites on the plasma membrane was likewise reduced following excision of the tissue. Presence of exogenous auxin in the preincubation medium prevented the decay of both auxin transport and the putative auxin efflux carriers. These results suggest that polar auxin transport in corn coleoptiles is autoregulated by endogenous auxin level through its influence on the auxin efflux carrier.