Melatonin promotes adventitious- and lateral root regeneration in etiolated hypocotyls of Lupinus albus L.

Melatonin is a well-known animal substance, which has recently been detected in plant tissues. However, there are only a few studies concerning its possible physiological role in plants. In this paper, we investigate the possible effect of melatonin on the regeneration of lateral and adventious roots in etiolated hypocotyls of Lupinus albus L. compared with the effect of indole-3-acetic acid. We performed this study by measuring both molecules in roots. Six-day-old derooted lupin hypocotyls immersed in several melatonin or indole-3-acetic acid concentrations were used to induce roots. A macro- and microscopic study of the histological origin of the adventitious and lateral roots was made, while melatonin and indole-3-acetic acid in the roots were quantified using liquid chromatography with fluorescence detection. The data show that both melatonin and indole-3-acetic acid induced the appearance of root primordia from pericicle cells, modifying the pattern of distribution of adventitious or lateral roots, the time-course, the number and length of adventitious roots, and the number of lateral roots. Melatonin and indole-3-acetic acid were detected and quantified in lupin primary roots, where both molecules were present in similar concentrations. The physiological effect of exogenous melatonin as root promoter was demonstrated, its action being similar to that of indole-3-acetic acid.