STIMULATION OF ADVENTITIOUS ROOTING IN SUNFLOWER (HELIANTHUS-ANNUUS) BY LOW PH - POSSIBLE ROLE OF AUXIN

Adventitious root formation by the hypocotyl cuttings of sunflower seedlings was greatly affected by the pH of buffered and unbuffered solutions bathing their basal portion. Exposure to low pH for 5 h after original root excision promoted root formation. Reduction of endogenous indole-3-acetic acid movement from the cotyledons and shoot apex was achieved by using N-1-naphthylphthalamic acid (an inhibitor of indole-3-acetic acid transport) and by removal of the cotyledons and shoot apex. Both the inhibitor and organ removal inhibited adventitious root formation, but acidic conditions could, to varying degrees, overcome this inhibition. Acidic conditions also increased the rate of [H-3]indole-3-acetic acid uptake from the solutions around the hypocotyl bases and the rate of [H-3]indole-3-acetic acid movement from cotyledons to the hypocotyl bases. Thus, acidic conditions may stimulate rooting by increasing the rate of basipetal indole-3-acetic acid transport to the zone of root initiation. These experiments show that in studies of the effects of various substances on rooting, the experimenter must be aware of these pH effects and take appropriate precautions.