Role of Auxin in Root Primordium Formation in Etiolated ‘Red Kidney’ Bean Stems1

Abstract When hypocotyls of intact ‘Red Kidney’ beans ( Phaseolus vulgaris L.) were wrapped with black plastic sheets, visible root primordia appeared within 12 days. No root primordium appeared in hypocotyls wrapped with clear plastic sheets. Etiolation did not stimulate formation of root primordium when shoots above the cotyledons were removed, but stimulated formation when shoots were replaced with lanolin containing indoleacetic acid (IAA), indolebutyric acid (IBA), or naphthaleneacetic acid (NAA). Even non-etiolated hypocotyls produced root primordia when auxin concentration in the lanolin was high. Etiolation treatment was more effective in root primordium formation when auxin supply was low. Pretreatment of hypocotyls with etiolation with shoots above the cotyledons removed did not stimulate the formation of root primordium in subsequently detached hypocotyl cuttings. Etiolation treatment did not significantly change the auxin concentration in the etiolated parts. These results suggest that etiolation stimulated root initiation by increasing the sensitivity of the stem to auxin.