Petiole growth auxin

There is evidence that the growth of petioles is dependent on auxin from the blade. Blade removal in Helianthus inhibits petiole elongation about 90%, an effect which is partially overcome if auxin is supplied to the cut surface of the petiole (Palmer 1972). Application of auxin to either the upper or lower surfaces of debladed petioles causes an increase in growth rate. Dayanadan et al. (1976) have found that auxin, but not GA or kinetin, promotes cell elongation in parenchyma, collenchyma and vascular elements of the sheath pulvinus of Avena leaves. 

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