The Role of Leaves in Auxin and Boron‐dependent Rooting of Stem Cuttings of Phaseolus Aureus Roxb.

SUMMARY The promotion of rooting of cuttings of Phaseolus aureus by indolebutyric acid (IBA) occurs only when leaves are present. IBA may have some direct action on root initiation in the hypocotyl but its main action is in the leaves where it leads to an early increase in free sugars. A later increase in sugars in the hypocotyl is largely dependent on exogenous boron which is essential for root development in cuttings of light‐grown material. IBA also stimulates and boron promotes the accumulation of l4 C in hypocotyls when [ l4 C]sucrose is applied to the leaves. These events occur before roots develop on the hypocotyl. Illumination of the leaves of cuttings during the rooting treatment (IBA for 1 day, followed by boron for 6 days) is beneficial for root development. A progressive loss of response to IBA and boron by cuttings aged in water prior to the rooting treatment is greater in cuttings with leaves in the light during the period of ageing than with leaves in darkness. Possible roles of leaves, auxin and boron in rooting are discussed.