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Treatment with indolebutyric acid (IBA) enhances root regeneration in stem cuttings of mung bean (Phaseolus aureus Roxb.) provided cuttings are supplied with borate. Treatment also increases the content of RNA in hypocotyls although RNA synthesis is inhibited by such treatment. Cell division in phloem parenchyma cells is evident 24 h after cuttings are prepared, irrespective of treatment with, or without, IBA. Following the preparation of cuttings, synthesis of RNA increases in the hypocotyl prior to the earliest mitoses in these cells and continues to increase in the presence of supplied borate. Autoradiographic investigation shows that, in the absence of supplied borate, synthesis of IBA within the nucleus decreases markedly in IBA-treated cuttings 40 h after cuttings are made. Moreover, RNA synthesis is totally inhibited 24 h later whereas cell division does not cease until 60 h. Witholding supply of boron for up to 72 h after cuttings are made has no effect on DNA synthesis. [ABSTRACT FROM AUTHOR]

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 14C in hypocotyls when [14C]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. [ABSTRACT FROM AUTHOR]